[PATCH v5.5 00/30] KVM: Scalable memslots implementation

[PATCH v5.5 00/30] KVM: Scalable memslots implementation

[Sean Christopherson]

This series is an iteration of Maciej's scalable memslots work.  It
addresses most, but not all, of my feedback from v5, hence the "5.5"
moniker.  Specifically, I did not touch the iteration over gfn and hva
ranges as I would likely do more harm than good, especially in the gfn
iterator.

The core functionality of the series is unchanged from v5 (or at least,
it should be).  Patches "Resolve memslot ID via a hash table" and "Keep
memslots in tree-based structures" are heavily reworked (the latter in
particular) to provide better continuity between patches and to avoid
the swap() logic when working with the "inactive" set of memslots.  But
again, the changes are intended to be purely cosmetic.

Paolo, ideally I'd like get to patch 03 (and therefore patch 02) into 5.16.
The patch technically breaks backwards compatibility with 32-bit KVM, but
I'm quite confident none of the existing 32-bit architectures can possibly
work.  RISC-V is the one exception where it's not obvious that creating
more guest memslot pages than can fit in an unsigned long won't fall on its
face.  Since RISC-V is new in 5.16, I'd like to get that change in before
RISC-V can gain any users doing bizarre things.

s390 folks, please look closely at patch 11, "KVM: s390: Use "new" memslot
instead of userspace memory region".  There's a subtle/weird functional
change in there that I can't imagine would negatively affect userspace,
but the end result is odd nonetheless.

Claudio, I dropped your R-b from "KVM: Integrate gfn_to_memslot_approx()
into search_memslots()" because I changed the code enough to break the s390
build at least once :-)

Patches 01 and 02 are bug fixes.

Patch 03 is fix of sorts to require that the total number of pages across
all memslots fit in an unsigned long.  The existing 32-bit KVM
architectures don't correctly handle this case, and fixing those issues
would quite gross and a waste of time.

Patches 04-18 are cleanups throughout common KVM and all architectures
to fix some warts in the memslot APIs that allow for a cleaner (IMO)
of the tree-based memslots code.  They also prep for more improvements
that are realized in the final patch.

Patches 19-28 are the core of Maciej's scalable memslots work.

Patches 29-30 take advantage of the tree-based memslots to avoid creating
a dummy "new" memslot on the stack, which simplifies the MOVE case and
aligns it with the other three memslot update cases.

v5.5
  * Add all the pre- and post-work cleanups.
  * Rebase to kvm/queue, commit 0d7d84498fb4 ("KVM: x86: SGX must...")
  * Name innermost helper ____gfn_to_memslot() instead of ...approx. [Sean]
  * Rework hash list patch and all subsequent tree modifications to use
    common kvm_memslot_replace() helper. [Sean]
  * Rework tree-based approach to avoid swap() by always pulling the
    invalid memslot tree on-demand, and by relying on precise variables
    names and comments (for the invidual memslot pointers).

v5:
  * https://lkml.kernel.org/r/cover.1632171478.git.maciej.szmigiero@oracle.com
  * Rebase onto v5.15-rc2 (torvalds/master),
  * Fix 64-bit division of n_memslots_pages for 32-bit KVM,
  * Collect Claudio's Reviewed-by tags for some of the patches.

Early history can be found in the above lore link.
 
Maciej S. Szmigiero (10):
  KVM: Resync only arch fields when slots_arch_lock gets reacquired
  KVM: x86: Use nr_memslot_pages to avoid traversing the memslots array
  KVM: Integrate gfn_to_memslot_approx() into search_memslots()
  KVM: Move WARN on invalid memslot index to update_memslots()
  KVM: Resolve memslot ID via a hash table instead of via a static array
  KVM: Use interval tree to do fast hva lookup in memslots
  KVM: s390: Introduce kvm_s390_get_gfn_end()
  KVM: Keep memslots in tree-based structures instead of array-based
    ones
  KVM: Optimize gfn lookup in kvm_zap_gfn_range()
  KVM: Optimize overlapping memslots check

Sean Christopherson (20):
  KVM: Ensure local memslot copies operate on up-to-date arch-specific
    data
  KVM: Disallow user memslot with size that exceeds "unsigned long"
  KVM: Require total number of memslot pages to fit in an unsigned long
  KVM: Open code kvm_delete_memslot() into its only caller
  KVM: Use "new" memslot's address space ID instead of dedicated param
  KVM: Let/force architectures to deal with arch specific memslot data
  KVM: arm64: Use "new" memslot instead of userspace memory region
  KVM: MIPS: Drop pr_debug from memslot commit to avoid using "mem"
  KVM: PPC: Avoid referencing userspace memory region in memslot updates
  KVM: s390: Use "new" memslot instead of userspace memory region
  KVM: x86: Use "new" memslot instead of userspace memory region
  KVM: RISC-V: Use "new" memslot instead of userspace memory region
  KVM: Stop passing kvm_userspace_memory_region to arch memslot hooks
  KVM: Use prepare/commit hooks to handle generic memslot metadata
    updates
  KVM: x86: Don't assume old/new memslots are non-NULL at memslot commit
  KVM: s390: Skip gfn/size sanity checks on memslot DELETE or FLAGS_ONLY
  KVM: Don't make a full copy of the old memslot in
    __kvm_set_memory_region()
  KVM: x86: Don't call kvm_mmu_change_mmu_pages() if the count hasn't
    changed
  KVM: Wait 'til the bitter end to initialize the "new" memslot
  KVM: Dynamically allocate "new" memslots from the get-go

 arch/arm64/kvm/Kconfig              |   1 +
 arch/arm64/kvm/mmu.c                |  27 +-
 arch/mips/kvm/Kconfig               |   1 +
 arch/mips/kvm/mips.c                |   9 +-
 arch/powerpc/include/asm/kvm_ppc.h  |  18 +-
 arch/powerpc/kvm/Kconfig            |   1 +
 arch/powerpc/kvm/book3s.c           |  14 +-
 arch/powerpc/kvm/book3s_64_mmu_hv.c |   4 +-
 arch/powerpc/kvm/book3s_hv.c        |  28 +-
 arch/powerpc/kvm/book3s_hv_nested.c |   4 +-
 arch/powerpc/kvm/book3s_hv_uvmem.c  |  14 +-
 arch/powerpc/kvm/book3s_pr.c        |  17 +-
 arch/powerpc/kvm/booke.c            |   7 +-
 arch/powerpc/kvm/powerpc.c          |   9 +-
 arch/riscv/kvm/mmu.c                |  34 +-
 arch/s390/kvm/Kconfig               |   1 +
 arch/s390/kvm/kvm-s390.c            |  98 ++--
 arch/s390/kvm/kvm-s390.h            |  14 +
 arch/s390/kvm/pv.c                  |   4 +-
 arch/x86/include/asm/kvm_host.h     |   1 -
 arch/x86/kvm/Kconfig                |   1 +
 arch/x86/kvm/debugfs.c              |   6 +-
 arch/x86/kvm/mmu/mmu.c              |  39 +-
 arch/x86/kvm/x86.c                  |  42 +-
 include/linux/kvm_host.h            | 240 +++++---
 virt/kvm/kvm_main.c                 | 868 ++++++++++++++++------------
 26 files changed, 855 insertions(+), 647 deletions(-)

-- 
2.33.1.1089.g2158813163f-goog

[PATCH v5.5 01/30] KVM: Ensure local memslot copies operate on up-to-date arch-specific data

[Sean Christopherson]

When modifying memslots, snapshot the "old" memslot and copy it to the
"new" memslot's arch data after (re)acquiring slots_arch_lock.  x86 can
change a memslot's arch data while memslot updates are in-progress so
long as it holds slots_arch_lock, thus snapshotting a memslot without
holding the lock can result in the consumption of stale data.

Fixes: b10a038e84d1 ("KVM: mmu: Add slots_arch_lock for memslot arch fields")
Cc: stable@vger.kernel.org
Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 virt/kvm/kvm_main.c | 47 ++++++++++++++++++++++++++++++---------------
 1 file changed, 31 insertions(+), 16 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 3f6d450355f0..99e69375c4c9 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1531,11 +1531,10 @@ static struct kvm_memslots *kvm_dup_memslots(struct kvm_memslots *old,
 
 static int kvm_set_memslot(struct kvm *kvm,
 			   const struct kvm_userspace_memory_region *mem,
-			   struct kvm_memory_slot *old,
 			   struct kvm_memory_slot *new, int as_id,
 			   enum kvm_mr_change change)
 {
-	struct kvm_memory_slot *slot;
+	struct kvm_memory_slot *slot, old;
 	struct kvm_memslots *slots;
 	int r;
 
@@ -1566,7 +1565,7 @@ static int kvm_set_memslot(struct kvm *kvm,
 		 * Note, the INVALID flag needs to be in the appropriate entry
 		 * in the freshly allocated memslots, not in @old or @new.
 		 */
-		slot = id_to_memslot(slots, old->id);
+		slot = id_to_memslot(slots, new->id);
 		slot->flags |= KVM_MEMSLOT_INVALID;
 
 		/*
@@ -1597,6 +1596,26 @@ static int kvm_set_memslot(struct kvm *kvm,
 		kvm_copy_memslots(slots, __kvm_memslots(kvm, as_id));
 	}
 
+	/*
+	 * Make a full copy of the old memslot, the pointer will become stale
+	 * when the memslots are re-sorted by update_memslots(), and the old
+	 * memslot needs to be referenced after calling update_memslots(), e.g.
+	 * to free its resources and for arch specific behavior.  This needs to
+	 * happen *after* (re)acquiring slots_arch_lock.
+	 */
+	slot = id_to_memslot(slots, new->id);
+	if (slot) {
+		old = *slot;
+	} else {
+		WARN_ON_ONCE(change != KVM_MR_CREATE);
+		memset(&old, 0, sizeof(old));
+		old.id = new->id;
+		old.as_id = as_id;
+	}
+
+	/* Copy the arch-specific data, again after (re)acquiring slots_arch_lock. */
+	memcpy(&new->arch, &old.arch, sizeof(old.arch));
+
 	r = kvm_arch_prepare_memory_region(kvm, new, mem, change);
 	if (r)
 		goto out_slots;
@@ -1604,14 +1623,18 @@ static int kvm_set_memslot(struct kvm *kvm,
 	update_memslots(slots, new, change);
 	slots = install_new_memslots(kvm, as_id, slots);
 
-	kvm_arch_commit_memory_region(kvm, mem, old, new, change);
+	kvm_arch_commit_memory_region(kvm, mem, &old, new, change);
+
+	/* Free the old memslot's metadata.  Note, this is the full copy!!! */
+	if (change == KVM_MR_DELETE)
+		kvm_free_memslot(kvm, &old);
 
 	kvfree(slots);
 	return 0;
 
 out_slots:
 	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) {
-		slot = id_to_memslot(slots, old->id);
+		slot = id_to_memslot(slots, new->id);
 		slot->flags &= ~KVM_MEMSLOT_INVALID;
 		slots = install_new_memslots(kvm, as_id, slots);
 	} else {
@@ -1626,7 +1649,6 @@ static int kvm_delete_memslot(struct kvm *kvm,
 			      struct kvm_memory_slot *old, int as_id)
 {
 	struct kvm_memory_slot new;
-	int r;
 
 	if (!old->npages)
 		return -EINVAL;
@@ -1639,12 +1661,7 @@ static int kvm_delete_memslot(struct kvm *kvm,
 	 */
 	new.as_id = as_id;
 
-	r = kvm_set_memslot(kvm, mem, old, &new, as_id, KVM_MR_DELETE);
-	if (r)
-		return r;
-
-	kvm_free_memslot(kvm, old);
-	return 0;
+	return kvm_set_memslot(kvm, mem, &new, as_id, KVM_MR_DELETE);
 }
 
 /*
@@ -1718,7 +1735,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	if (!old.npages) {
 		change = KVM_MR_CREATE;
 		new.dirty_bitmap = NULL;
-		memset(&new.arch, 0, sizeof(new.arch));
 	} else { /* Modify an existing slot. */
 		if ((new.userspace_addr != old.userspace_addr) ||
 		    (new.npages != old.npages) ||
@@ -1732,9 +1748,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		else /* Nothing to change. */
 			return 0;
 
-		/* Copy dirty_bitmap and arch from the current memslot. */
+		/* Copy dirty_bitmap from the current memslot. */
 		new.dirty_bitmap = old.dirty_bitmap;
-		memcpy(&new.arch, &old.arch, sizeof(new.arch));
 	}
 
 	if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
@@ -1760,7 +1775,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			bitmap_set(new.dirty_bitmap, 0, new.npages);
 	}
 
-	r = kvm_set_memslot(kvm, mem, &old, &new, as_id, change);
+	r = kvm_set_memslot(kvm, mem, &new, as_id, change);
 	if (r)
 		goto out_bitmap;
 
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 01/30] KVM: Ensure local memslot copies operate on up-to-date arch-specific data

[Ben Gardon]

On Wed, Nov 3, 2021 at 5:26 PM Sean Christopherson <seanjc@google.com> wrote:
>
> When modifying memslots, snapshot the "old" memslot and copy it to the
> "new" memslot's arch data after (re)acquiring slots_arch_lock.  x86 can
> change a memslot's arch data while memslot updates are in-progress so
> long as it holds slots_arch_lock, thus snapshotting a memslot without
> holding the lock can result in the consumption of stale data.
>
> Fixes: b10a038e84d1 ("KVM: mmu: Add slots_arch_lock for memslot arch fields")
> Cc: stable@vger.kernel.org
> Cc: Ben Gardon <bgardon@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  virt/kvm/kvm_main.c | 47 ++++++++++++++++++++++++++++++---------------
>  1 file changed, 31 insertions(+), 16 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 3f6d450355f0..99e69375c4c9 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1531,11 +1531,10 @@ static struct kvm_memslots *kvm_dup_memslots(struct kvm_memslots *old,
>
>  static int kvm_set_memslot(struct kvm *kvm,
>                            const struct kvm_userspace_memory_region *mem,
> -                          struct kvm_memory_slot *old,
>                            struct kvm_memory_slot *new, int as_id,
>                            enum kvm_mr_change change)
>  {
> -       struct kvm_memory_slot *slot;
> +       struct kvm_memory_slot *slot, old;
>         struct kvm_memslots *slots;
>         int r;
>
> @@ -1566,7 +1565,7 @@ static int kvm_set_memslot(struct kvm *kvm,
>                  * Note, the INVALID flag needs to be in the appropriate entry
>                  * in the freshly allocated memslots, not in @old or @new.
>                  */
> -               slot = id_to_memslot(slots, old->id);
> +               slot = id_to_memslot(slots, new->id);

Since new is guaranteed to have the same id as old (at least prior to
this change) this is a no-op change, so no problem here.
This could be a separate commit which would have no functional change
but only worth extracting if you send a v2.

>                 slot->flags |= KVM_MEMSLOT_INVALID;
>
>                 /*
> @@ -1597,6 +1596,26 @@ static int kvm_set_memslot(struct kvm *kvm,
>                 kvm_copy_memslots(slots, __kvm_memslots(kvm, as_id));
>         }
>
> +       /*
> +        * Make a full copy of the old memslot, the pointer will become stale
> +        * when the memslots are re-sorted by update_memslots(), and the old
> +        * memslot needs to be referenced after calling update_memslots(), e.g.
> +        * to free its resources and for arch specific behavior.  This needs to
> +        * happen *after* (re)acquiring slots_arch_lock.
> +        */
> +       slot = id_to_memslot(slots, new->id);
> +       if (slot) {
> +               old = *slot;
> +       } else {
> +               WARN_ON_ONCE(change != KVM_MR_CREATE);
> +               memset(&old, 0, sizeof(old));
> +               old.id = new->id;
> +               old.as_id = as_id;
> +       }
> +
> +       /* Copy the arch-specific data, again after (re)acquiring slots_arch_lock. */
> +       memcpy(&new->arch, &old.arch, sizeof(old.arch));
> +

Is new->arch not initialized before this function is called? Does this
need to be here, or could it be moved above into the first branch of
the if statement?
Oh I see you removed the memset below and replaced it with this. I
think this is fine, but it might be easier to reason about if we left
the memset and moved the memcopy into the if.
No point in doing a memcpy of zeros here.

>         r = kvm_arch_prepare_memory_region(kvm, new, mem, change);
>         if (r)
>                 goto out_slots;
> @@ -1604,14 +1623,18 @@ static int kvm_set_memslot(struct kvm *kvm,
>         update_memslots(slots, new, change);
>         slots = install_new_memslots(kvm, as_id, slots);
>
> -       kvm_arch_commit_memory_region(kvm, mem, old, new, change);
> +       kvm_arch_commit_memory_region(kvm, mem, &old, new, change);
> +
> +       /* Free the old memslot's metadata.  Note, this is the full copy!!! */
> +       if (change == KVM_MR_DELETE)
> +               kvm_free_memslot(kvm, &old);
>
>         kvfree(slots);
>         return 0;
>
>  out_slots:
>         if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) {
> -               slot = id_to_memslot(slots, old->id);
> +               slot = id_to_memslot(slots, new->id);
>                 slot->flags &= ~KVM_MEMSLOT_INVALID;
>                 slots = install_new_memslots(kvm, as_id, slots);
>         } else {
> @@ -1626,7 +1649,6 @@ static int kvm_delete_memslot(struct kvm *kvm,
>                               struct kvm_memory_slot *old, int as_id)
>  {
>         struct kvm_memory_slot new;
> -       int r;
>
>         if (!old->npages)
>                 return -EINVAL;
> @@ -1639,12 +1661,7 @@ static int kvm_delete_memslot(struct kvm *kvm,
>          */
>         new.as_id = as_id;
>
> -       r = kvm_set_memslot(kvm, mem, old, &new, as_id, KVM_MR_DELETE);
> -       if (r)
> -               return r;
> -
> -       kvm_free_memslot(kvm, old);
> -       return 0;
> +       return kvm_set_memslot(kvm, mem, &new, as_id, KVM_MR_DELETE);
>  }
>
>  /*
> @@ -1718,7 +1735,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
>         if (!old.npages) {
>                 change = KVM_MR_CREATE;
>                 new.dirty_bitmap = NULL;
> -               memset(&new.arch, 0, sizeof(new.arch));
>         } else { /* Modify an existing slot. */
>                 if ((new.userspace_addr != old.userspace_addr) ||
>                     (new.npages != old.npages) ||
> @@ -1732,9 +1748,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
>                 else /* Nothing to change. */
>                         return 0;
>
> -               /* Copy dirty_bitmap and arch from the current memslot. */
> +               /* Copy dirty_bitmap from the current memslot. */
>                 new.dirty_bitmap = old.dirty_bitmap;
> -               memcpy(&new.arch, &old.arch, sizeof(new.arch));
>         }
>
>         if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
> @@ -1760,7 +1775,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
>                         bitmap_set(new.dirty_bitmap, 0, new.npages);
>         }
>
> -       r = kvm_set_memslot(kvm, mem, &old, &new, as_id, change);
> +       r = kvm_set_memslot(kvm, mem, &new, as_id, change);
>         if (r)
>                 goto out_bitmap;
>
> --
> 2.33.1.1089.g2158813163f-goog
>

Re: [PATCH v5.5 01/30] KVM: Ensure local memslot copies operate on up-to-date arch-specific data

[Sean Christopherson]

On Thu, Nov 04, 2021, Ben Gardon wrote:
> > @@ -1597,6 +1596,26 @@ static int kvm_set_memslot(struct kvm *kvm,
> >                 kvm_copy_memslots(slots, __kvm_memslots(kvm, as_id));
> >         }
> >
> > +       /*
> > +        * Make a full copy of the old memslot, the pointer will become stale
> > +        * when the memslots are re-sorted by update_memslots(), and the old
> > +        * memslot needs to be referenced after calling update_memslots(), e.g.
> > +        * to free its resources and for arch specific behavior.  This needs to
> > +        * happen *after* (re)acquiring slots_arch_lock.
> > +        */
> > +       slot = id_to_memslot(slots, new->id);
> > +       if (slot) {
> > +               old = *slot;
> > +       } else {
> > +               WARN_ON_ONCE(change != KVM_MR_CREATE);
> > +               memset(&old, 0, sizeof(old));
> > +               old.id = new->id;
> > +               old.as_id = as_id;
> > +       }
> > +
> > +       /* Copy the arch-specific data, again after (re)acquiring slots_arch_lock. */
> > +       memcpy(&new->arch, &old.arch, sizeof(old.arch));
> > +
> 
> Is new->arch not initialized before this function is called? Does this
> need to be here, or could it be moved above into the first branch of
> the if statement?
> Oh I see you removed the memset below and replaced it with this. I
> think this is fine, but it might be easier to reason about if we left
> the memset and moved the memcopy into the if.
> No point in doing a memcpy of zeros here.

Hmm, good point.  I wrote it like this so that the "arch" part is more identifiable
since that's what needs to be protected by the lock, but I completely agree that
it's odd when viewed without that lens.

Re: [PATCH v5.5 01/30] KVM: Ensure local memslot copies operate on up-to-date arch-specific data

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> When modifying memslots, snapshot the "old" memslot and copy it to the
> "new" memslot's arch data after (re)acquiring slots_arch_lock.  x86 can
> change a memslot's arch data while memslot updates are in-progress so
> long as it holds slots_arch_lock, thus snapshotting a memslot without
> holding the lock can result in the consumption of stale data.
> 
> Fixes: b10a038e84d1 ("KVM: mmu: Add slots_arch_lock for memslot arch fields")
> Cc: stable@vger.kernel.org
> Cc: Ben Gardon <bgardon@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   virt/kvm/kvm_main.c | 47 ++++++++++++++++++++++++++++++---------------
>   1 file changed, 31 insertions(+), 16 deletions(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 3f6d450355f0..99e69375c4c9 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1531,11 +1531,10 @@ static struct kvm_memslots *kvm_dup_memslots(struct kvm_memslots *old,
>   
>   static int kvm_set_memslot(struct kvm *kvm,
>   			   const struct kvm_userspace_memory_region *mem,
> -			   struct kvm_memory_slot *old,
>   			   struct kvm_memory_slot *new, int as_id,
>   			   enum kvm_mr_change change)
>   {
> -	struct kvm_memory_slot *slot;
> +	struct kvm_memory_slot *slot, old;
>   	struct kvm_memslots *slots;
>   	int r;
>   
> @@ -1566,7 +1565,7 @@ static int kvm_set_memslot(struct kvm *kvm,
>   		 * Note, the INVALID flag needs to be in the appropriate entry
>   		 * in the freshly allocated memslots, not in @old or @new.
>   		 */
> -		slot = id_to_memslot(slots, old->id);
> +		slot = id_to_memslot(slots, new->id);
>   		slot->flags |= KVM_MEMSLOT_INVALID;
>   
>   		/*
> @@ -1597,6 +1596,26 @@ static int kvm_set_memslot(struct kvm *kvm,
>   		kvm_copy_memslots(slots, __kvm_memslots(kvm, as_id));
>   	}
>   
> +	/*
> +	 * Make a full copy of the old memslot, the pointer will become stale
> +	 * when the memslots are re-sorted by update_memslots(), and the old
> +	 * memslot needs to be referenced after calling update_memslots(), e.g.
> +	 * to free its resources and for arch specific behavior.  This needs to
> +	 * happen *after* (re)acquiring slots_arch_lock.
> +	 */
> +	slot = id_to_memslot(slots, new->id);
> +	if (slot) {
> +		old = *slot;
> +	} else {
> +		WARN_ON_ONCE(change != KVM_MR_CREATE);
> +		memset(&old, 0, sizeof(old));
> +		old.id = new->id;
> +		old.as_id = as_id;
> +	}
> +
> +	/* Copy the arch-specific data, again after (re)acquiring slots_arch_lock. */
> +	memcpy(&new->arch, &old.arch, sizeof(old.arch));

Had "new" been zero-initialized completely in __kvm_set_memory_region()
for safety (so it does not contain stack garbage - I don't mean just the
new.arch field in the "if (!old.npages)" branch in that function but the
whole struct) this line would be needed only in the "if (slot)" branch
above (as Ben said).

Also, when patch 7 from this series removes this memcpy(),
kvm_arch_prepare_memory_region() does indeed receive this field
uninitialized - I know only x86 and ppcHV care
and kvm_alloc_memslot_metadata() or kvmppc_core_prepare_memory_region_hv()
then overwrites it unconditionally but it feels a bit wrong.

I am almost certain that compiler would figure out to only actually
zero the fields that wouldn't be overwritten immediately anyway.

But on the other hand, this patch is only a fix for code that's going
to be replaced anyway so perfection here probably isn't that important.

Thanks,
Maciej

Re: [PATCH v5.5 01/30] KVM: Ensure local memslot copies operate on up-to-date arch-specific data

[Sean Christopherson]

On Tue, Nov 09, 2021, Maciej S. Szmigiero wrote:
> On 04.11.2021 01:25, Sean Christopherson wrote:
> > @@ -1597,6 +1596,26 @@ static int kvm_set_memslot(struct kvm *kvm,
> >   		kvm_copy_memslots(slots, __kvm_memslots(kvm, as_id));
> >   	}
> > +	/*
> > +	 * Make a full copy of the old memslot, the pointer will become stale
> > +	 * when the memslots are re-sorted by update_memslots(), and the old
> > +	 * memslot needs to be referenced after calling update_memslots(), e.g.
> > +	 * to free its resources and for arch specific behavior.  This needs to
> > +	 * happen *after* (re)acquiring slots_arch_lock.
> > +	 */
> > +	slot = id_to_memslot(slots, new->id);
> > +	if (slot) {
> > +		old = *slot;
> > +	} else {
> > +		WARN_ON_ONCE(change != KVM_MR_CREATE);
> > +		memset(&old, 0, sizeof(old));
> > +		old.id = new->id;
> > +		old.as_id = as_id;
> > +	}
> > +
> > +	/* Copy the arch-specific data, again after (re)acquiring slots_arch_lock. */
> > +	memcpy(&new->arch, &old.arch, sizeof(old.arch));
> 
> Had "new" been zero-initialized completely in __kvm_set_memory_region()
> for safety (so it does not contain stack garbage - I don't mean just the
> new.arch field in the "if (!old.npages)" branch in that function but the
> whole struct) this line would be needed only in the "if (slot)" branch
> above (as Ben said).
> 
> Also, when patch 7 from this series removes this memcpy(),
> kvm_arch_prepare_memory_region() does indeed receive this field
> uninitialized - I know only x86 and ppcHV care
> and kvm_alloc_memslot_metadata() or kvmppc_core_prepare_memory_region_hv()
> then overwrites it unconditionally but it feels a bit wrong.
> 
> I am almost certain that compiler would figure out to only actually
> zero the fields that wouldn't be overwritten immediately anyway.
> 
> But on the other hand, this patch is only a fix for code that's going
> to be replaced anyway so perfection here probably isn't that important.

Yeah, that about sums up my feelings about the existing code.  That said, an
individual memslot isn't _that_ big, and memslot updates without the scalable
implementation are dreadfully slow anyways, so I'm leaning strongly toward your
suggestion of zeroing all of new as part of this fix.

[PATCH v5.5 02/30] KVM: Disallow user memslot with size that exceeds "unsigned long"

[Sean Christopherson]

Reject userspace memslots whose size exceeds the storage capacity of an
"unsigned long".  KVM's uAPI takes the size as u64 to support large slots
on 64-bit hosts, but does not account for the size being truncated on
32-bit hosts in various flows.  The access_ok() check on the userspace
virtual address in particular casts the size to "unsigned long" and will
check the wrong number of bytes.

KVM doesn't actually support slots whose size doesn't fit in an "unsigned
long", e.g. KVM's internal kvm_memory_slot.npages is an "unsigned long",
not a "u64", and misc arch specific code follows that behavior.

Fixes: fa3d315a4ce2 ("KVM: Validate userspace_addr of memslot when registered")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 virt/kvm/kvm_main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 99e69375c4c9..83287730389f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1689,7 +1689,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	id = (u16)mem->slot;
 
 	/* General sanity checks */
-	if (mem->memory_size & (PAGE_SIZE - 1))
+	if ((mem->memory_size & (PAGE_SIZE - 1)) ||
+	    (mem->memory_size != (unsigned long)mem->memory_size))
 		return -EINVAL;
 	if (mem->guest_phys_addr & (PAGE_SIZE - 1))
 		return -EINVAL;
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 02/30] KVM: Disallow user memslot with size that exceeds "unsigned long"

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> Reject userspace memslots whose size exceeds the storage capacity of an
> "unsigned long".  KVM's uAPI takes the size as u64 to support large slots
> on 64-bit hosts, but does not account for the size being truncated on
> 32-bit hosts in various flows.  The access_ok() check on the userspace
> virtual address in particular casts the size to "unsigned long" and will
> check the wrong number of bytes.
> 
> KVM doesn't actually support slots whose size doesn't fit in an "unsigned
> long", e.g. KVM's internal kvm_memory_slot.npages is an "unsigned long",
> not a "u64", and misc arch specific code follows that behavior.
> 
> Fixes: fa3d315a4ce2 ("KVM: Validate userspace_addr of memslot when registered")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   virt/kvm/kvm_main.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 99e69375c4c9..83287730389f 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1689,7 +1689,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
>   	id = (u16)mem->slot;
>   
>   	/* General sanity checks */
> -	if (mem->memory_size & (PAGE_SIZE - 1))
> +	if ((mem->memory_size & (PAGE_SIZE - 1)) ||
> +	    (mem->memory_size != (unsigned long)mem->memory_size))
>   		return -EINVAL;
>   	if (mem->guest_phys_addr & (PAGE_SIZE - 1))
>   		return -EINVAL;
> 

Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

[PATCH v5.5 03/30] KVM: Require total number of memslot pages to fit in an unsigned long

[Sean Christopherson]

Explicitly disallow creating more memslot pages than can fit in an
unsigned long, KVM doesn't correctly handle a total number of memslot
pages that doesn't fit in an unsigned long and remedying that would be a
waste of time.

For a 64-bit kernel, this is a nop as memslots are not allowed to overlap
in the gfn address space.

With a 32-bit kernel, userspace can at most address 3gb of virtual memory,
whereas wrapping the total number of pages would require 4tb+ of guest
physical memory.  Even with x86's second address space for SMM, userspace
would need to alias all of guest memory more than one _thousand_ times.
And on older x86 hardware with MAXPHYADDR < 43, the guest couldn't
actually access any of those aliases even if userspace lied about
guest.MAXPHYADDR.

On 390 and arm64, this is a nop as they don't support 32-bit hosts.

On x86, practically speaking this is simply acknowledging reality as the
existing kvm_mmu_calculate_default_mmu_pages() assumes the total number
of pages fits in an "unsigned long".

On PPC, this is likely a nop as every flavor of PPC KVM assumes gfns (and
gpas!) fit in unsigned long.  arch/powerpc/kvm/book3s_32_mmu_host.c goes
a step further and fails the build if CONFIG_PTE_64BIT=y, which
presumably means that it does't support 64-bit physical addresses.

On MIPS, this is also likely a nop as the core MMU helpers assume gpas
fit in unsigned long, e.g. see kvm_mips_##name##_pte.

And finally, RISC-V is a "don't care" as it doesn't exist in any release,
i.e. there is no established ABI to break.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 include/linux/kvm_host.h |  1 +
 virt/kvm/kvm_main.c      | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 60a35d9fe259..d8e92d4a78d8 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -551,6 +551,7 @@ struct kvm {
 	 */
 	struct mutex slots_arch_lock;
 	struct mm_struct *mm; /* userspace tied to this vm */
+	unsigned long nr_memslot_pages;
 	struct kvm_memslots __rcu *memslots[KVM_ADDRESS_SPACE_NUM];
 	struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 83287730389f..264c4b16520b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1623,6 +1623,15 @@ static int kvm_set_memslot(struct kvm *kvm,
 	update_memslots(slots, new, change);
 	slots = install_new_memslots(kvm, as_id, slots);
 
+	/*
+	 * Update the total number of memslot pages before calling the arch
+	 * hook so that architectures can consume the result directly.
+	 */
+	if (change == KVM_MR_DELETE)
+		kvm->nr_memslot_pages -= old.npages;
+	else if (change == KVM_MR_CREATE)
+		kvm->nr_memslot_pages += new->npages;
+
 	kvm_arch_commit_memory_region(kvm, mem, &old, new, change);
 
 	/* Free the old memslot's metadata.  Note, this is the full copy!!! */
@@ -1653,6 +1662,9 @@ static int kvm_delete_memslot(struct kvm *kvm,
 	if (!old->npages)
 		return -EINVAL;
 
+	if (WARN_ON_ONCE(kvm->nr_memslot_pages < old->npages))
+		return -EIO;
+
 	memset(&new, 0, sizeof(new));
 	new.id = old->id;
 	/*
@@ -1736,6 +1748,13 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	if (!old.npages) {
 		change = KVM_MR_CREATE;
 		new.dirty_bitmap = NULL;
+
+		/*
+		 * To simplify KVM internals, the total number of pages across
+		 * all memslots must fit in an unsigned long.
+		 */
+		if ((kvm->nr_memslot_pages + new.npages) < kvm->nr_memslot_pages)
+			return -EINVAL;
 	} else { /* Modify an existing slot. */
 		if ((new.userspace_addr != old.userspace_addr) ||
 		    (new.npages != old.npages) ||
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 03/30] KVM: Require total number of memslot pages to fit in an unsigned long

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> Explicitly disallow creating more memslot pages than can fit in an
> unsigned long, KVM doesn't correctly handle a total number of memslot
> pages that doesn't fit in an unsigned long and remedying that would be a
> waste of time.
> 
> For a 64-bit kernel, this is a nop as memslots are not allowed to overlap
> in the gfn address space.
> 
> With a 32-bit kernel, userspace can at most address 3gb of virtual memory,
> whereas wrapping the total number of pages would require 4tb+ of guest
> physical memory.  Even with x86's second address space for SMM, userspace
> would need to alias all of guest memory more than one _thousand_ times.
> And on older x86 hardware with MAXPHYADDR < 43, the guest couldn't
> actually access any of those aliases even if userspace lied about
> guest.MAXPHYADDR.
> 
> On 390 and arm64, this is a nop as they don't support 32-bit hosts.
> 
> On x86, practically speaking this is simply acknowledging reality as the
> existing kvm_mmu_calculate_default_mmu_pages() assumes the total number
> of pages fits in an "unsigned long".
> 
> On PPC, this is likely a nop as every flavor of PPC KVM assumes gfns (and
> gpas!) fit in unsigned long.  arch/powerpc/kvm/book3s_32_mmu_host.c goes
> a step further and fails the build if CONFIG_PTE_64BIT=y, which
> presumably means that it does't support 64-bit physical addresses.
> 
> On MIPS, this is also likely a nop as the core MMU helpers assume gpas
> fit in unsigned long, e.g. see kvm_mips_##name##_pte.
> 
> And finally, RISC-V is a "don't care" as it doesn't exist in any release,
> i.e. there is no established ABI to break.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

[PATCH v5.5 04/30] KVM: Open code kvm_delete_memslot() into its only caller

[Sean Christopherson]

Fold kvm_delete_memslot() into __kvm_set_memory_region() to free up the
"kvm_delete_memslot()" name for use in a future helper.  The delete logic
isn't so complex/long that it truly needs a helper, and it will be
simplified a wee bit further in upcoming commits.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 virt/kvm/kvm_main.c | 42 +++++++++++++++++-------------------------
 1 file changed, 17 insertions(+), 25 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 264c4b16520b..6171ddb3e31c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1653,29 +1653,6 @@ static int kvm_set_memslot(struct kvm *kvm,
 	return r;
 }
 
-static int kvm_delete_memslot(struct kvm *kvm,
-			      const struct kvm_userspace_memory_region *mem,
-			      struct kvm_memory_slot *old, int as_id)
-{
-	struct kvm_memory_slot new;
-
-	if (!old->npages)
-		return -EINVAL;
-
-	if (WARN_ON_ONCE(kvm->nr_memslot_pages < old->npages))
-		return -EIO;
-
-	memset(&new, 0, sizeof(new));
-	new.id = old->id;
-	/*
-	 * This is only for debugging purpose; it should never be referenced
-	 * for a removed memslot.
-	 */
-	new.as_id = as_id;
-
-	return kvm_set_memslot(kvm, mem, &new, as_id, KVM_MR_DELETE);
-}
-
 /*
  * Allocate some memory and give it an address in the guest physical address
  * space.
@@ -1732,8 +1709,23 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		old.id = id;
 	}
 
-	if (!mem->memory_size)
-		return kvm_delete_memslot(kvm, mem, &old, as_id);
+	if (!mem->memory_size) {
+		if (!old.npages)
+			return -EINVAL;
+
+		if (WARN_ON_ONCE(kvm->nr_memslot_pages < old.npages))
+			return -EIO;
+
+		memset(&new, 0, sizeof(new));
+		new.id = id;
+		/*
+		 * This is only for debugging purpose; it should never be
+		 * referenced for a removed memslot.
+		 */
+		new.as_id = as_id;
+
+		return kvm_set_memslot(kvm, mem, &new, as_id, KVM_MR_DELETE);
+	}
 
 	new.as_id = as_id;
 	new.id = id;
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 04/30] KVM: Open code kvm_delete_memslot() into its only caller

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> Fold kvm_delete_memslot() into __kvm_set_memory_region() to free up the
> "kvm_delete_memslot()" name for use in a future helper.  The delete logic
> isn't so complex/long that it truly needs a helper, and it will be
> simplified a wee bit further in upcoming commits.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

[PATCH v5.5 05/30] KVM: Resync only arch fields when slots_arch_lock gets reacquired

[Sean Christopherson]

From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

There is no need to copy the whole memslot data after releasing
slots_arch_lock for a moment to install temporary memslots copy in
kvm_set_memslot() since this lock only protects the arch field of each
memslot.

Just resync this particular field after reacquiring slots_arch_lock.

Note, this also eliminates the need to manually clear the INVALID flag
when restoring memslots; the "setting" of the INVALID flag was an
unwanted side effect of copying the entire memslots.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
[sean: tweak shortlog, note INVALID flag in changelog, revert comment]
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 virt/kvm/kvm_main.c | 45 +++++++++++++++++++++++++--------------------
 1 file changed, 25 insertions(+), 20 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 6171ddb3e31c..e5c2d10f6111 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1500,12 +1500,6 @@ static size_t kvm_memslots_size(int slots)
 	       (sizeof(struct kvm_memory_slot) * slots);
 }
 
-static void kvm_copy_memslots(struct kvm_memslots *to,
-			      struct kvm_memslots *from)
-{
-	memcpy(to, from, kvm_memslots_size(from->used_slots));
-}
-
 /*
  * Note, at a minimum, the current number of used slots must be allocated, even
  * when deleting a memslot, as we need a complete duplicate of the memslots for
@@ -1524,11 +1518,22 @@ static struct kvm_memslots *kvm_dup_memslots(struct kvm_memslots *old,
 
 	slots = kvzalloc(new_size, GFP_KERNEL_ACCOUNT);
 	if (likely(slots))
-		kvm_copy_memslots(slots, old);
+		memcpy(slots, old, kvm_memslots_size(old->used_slots));
 
 	return slots;
 }
 
+static void kvm_copy_memslots_arch(struct kvm_memslots *to,
+				   struct kvm_memslots *from)
+{
+	int i;
+
+	WARN_ON_ONCE(to->used_slots != from->used_slots);
+
+	for (i = 0; i < from->used_slots; i++)
+		to->memslots[i].arch = from->memslots[i].arch;
+}
+
 static int kvm_set_memslot(struct kvm *kvm,
 			   const struct kvm_userspace_memory_region *mem,
 			   struct kvm_memory_slot *new, int as_id,
@@ -1569,9 +1574,10 @@ static int kvm_set_memslot(struct kvm *kvm,
 		slot->flags |= KVM_MEMSLOT_INVALID;
 
 		/*
-		 * We can re-use the memory from the old memslots.
-		 * It will be overwritten with a copy of the new memslots
-		 * after reacquiring the slots_arch_lock below.
+		 * We can re-use the old memslots, the only difference from the
+		 * newly installed memslots is the invalid flag, which will get
+		 * dropped by update_memslots anyway.  We'll also revert to the
+		 * old memslots if preparing the new memory region fails.
 		 */
 		slots = install_new_memslots(kvm, as_id, slots);
 
@@ -1588,12 +1594,14 @@ static int kvm_set_memslot(struct kvm *kvm,
 		mutex_lock(&kvm->slots_arch_lock);
 
 		/*
-		 * The arch-specific fields of the memslots could have changed
-		 * between releasing the slots_arch_lock in
-		 * install_new_memslots and here, so get a fresh copy of the
-		 * slots.
+		 * The arch-specific fields of the now-active memslots could
+		 * have been modified between releasing slots_arch_lock in
+		 * install_new_memslots and re-acquiring slots_arch_lock above.
+		 * Copy them to the inactive memslots.  Arch code is required
+		 * to retrieve memslots *after* acquiring slots_arch_lock, thus
+		 * the active memslots are guaranteed to be fresh.
 		 */
-		kvm_copy_memslots(slots, __kvm_memslots(kvm, as_id));
+		kvm_copy_memslots_arch(slots, __kvm_memslots(kvm, as_id));
 	}
 
 	/*
@@ -1642,13 +1650,10 @@ static int kvm_set_memslot(struct kvm *kvm,
 	return 0;
 
 out_slots:
-	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) {
-		slot = id_to_memslot(slots, new->id);
-		slot->flags &= ~KVM_MEMSLOT_INVALID;
+	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE)
 		slots = install_new_memslots(kvm, as_id, slots);
-	} else {
+	else
 		mutex_unlock(&kvm->slots_arch_lock);
-	}
 	kvfree(slots);
 	return r;
 }
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 05/30] KVM: Resync only arch fields when slots_arch_lock gets reacquired

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> 
> There is no need to copy the whole memslot data after releasing
> slots_arch_lock for a moment to install temporary memslots copy in
> kvm_set_memslot() since this lock only protects the arch field of each
> memslot.
> 
> Just resync this particular field after reacquiring slots_arch_lock.
> 
> Note, this also eliminates the need to manually clear the INVALID flag
> when restoring memslots; the "setting" of the INVALID flag was an
> unwanted side effect of copying the entire memslots.
> 
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> [sean: tweak shortlog, note INVALID flag in changelog, revert comment]

This updated patch also open-codes kvm_copy_memslots(), which my
previous version didn't.
I think it's worth mentioning this in the change log, too.

Thanks,
Maciej

[PATCH v5.5 06/30] KVM: Use "new" memslot's address space ID instead of dedicated param

[Sean Christopherson]

Now that the address space ID is stored in every slot, including fake
slots used for deletion, use the slot's as_id instead of passing in the
redundant information as a param to kvm_set_memslot().  This will greatly
simplify future memslot work by avoiding passing a large number of
variables around purely to honor @as_id.

Drop a comment in the DELETE path about new->as_id being provided purely
for debug, as that's now a lie.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 virt/kvm/kvm_main.c | 22 +++++++++-------------
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e5c2d10f6111..39a64e02a43a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1536,7 +1536,7 @@ static void kvm_copy_memslots_arch(struct kvm_memslots *to,
 
 static int kvm_set_memslot(struct kvm *kvm,
 			   const struct kvm_userspace_memory_region *mem,
-			   struct kvm_memory_slot *new, int as_id,
+			   struct kvm_memory_slot *new,
 			   enum kvm_mr_change change)
 {
 	struct kvm_memory_slot *slot, old;
@@ -1559,7 +1559,7 @@ static int kvm_set_memslot(struct kvm *kvm,
 	 */
 	mutex_lock(&kvm->slots_arch_lock);
 
-	slots = kvm_dup_memslots(__kvm_memslots(kvm, as_id), change);
+	slots = kvm_dup_memslots(__kvm_memslots(kvm, new->as_id), change);
 	if (!slots) {
 		mutex_unlock(&kvm->slots_arch_lock);
 		return -ENOMEM;
@@ -1579,7 +1579,7 @@ static int kvm_set_memslot(struct kvm *kvm,
 		 * dropped by update_memslots anyway.  We'll also revert to the
 		 * old memslots if preparing the new memory region fails.
 		 */
-		slots = install_new_memslots(kvm, as_id, slots);
+		slots = install_new_memslots(kvm, new->as_id, slots);
 
 		/* From this point no new shadow pages pointing to a deleted,
 		 * or moved, memslot will be created.
@@ -1601,7 +1601,7 @@ static int kvm_set_memslot(struct kvm *kvm,
 		 * to retrieve memslots *after* acquiring slots_arch_lock, thus
 		 * the active memslots are guaranteed to be fresh.
 		 */
-		kvm_copy_memslots_arch(slots, __kvm_memslots(kvm, as_id));
+		kvm_copy_memslots_arch(slots, __kvm_memslots(kvm, new->as_id));
 	}
 
 	/*
@@ -1618,7 +1618,7 @@ static int kvm_set_memslot(struct kvm *kvm,
 		WARN_ON_ONCE(change != KVM_MR_CREATE);
 		memset(&old, 0, sizeof(old));
 		old.id = new->id;
-		old.as_id = as_id;
+		old.as_id = new->as_id;
 	}
 
 	/* Copy the arch-specific data, again after (re)acquiring slots_arch_lock. */
@@ -1629,7 +1629,7 @@ static int kvm_set_memslot(struct kvm *kvm,
 		goto out_slots;
 
 	update_memslots(slots, new, change);
-	slots = install_new_memslots(kvm, as_id, slots);
+	slots = install_new_memslots(kvm, new->as_id, slots);
 
 	/*
 	 * Update the total number of memslot pages before calling the arch
@@ -1651,7 +1651,7 @@ static int kvm_set_memslot(struct kvm *kvm,
 
 out_slots:
 	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE)
-		slots = install_new_memslots(kvm, as_id, slots);
+		slots = install_new_memslots(kvm, new->as_id, slots);
 	else
 		mutex_unlock(&kvm->slots_arch_lock);
 	kvfree(slots);
@@ -1723,13 +1723,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
 
 		memset(&new, 0, sizeof(new));
 		new.id = id;
-		/*
-		 * This is only for debugging purpose; it should never be
-		 * referenced for a removed memslot.
-		 */
 		new.as_id = as_id;
 
-		return kvm_set_memslot(kvm, mem, &new, as_id, KVM_MR_DELETE);
+		return kvm_set_memslot(kvm, mem, &new, KVM_MR_DELETE);
 	}
 
 	new.as_id = as_id;
@@ -1792,7 +1788,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			bitmap_set(new.dirty_bitmap, 0, new.npages);
 	}
 
-	r = kvm_set_memslot(kvm, mem, &new, as_id, change);
+	r = kvm_set_memslot(kvm, mem, &new, change);
 	if (r)
 		goto out_bitmap;
 
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 06/30] KVM: Use "new" memslot's address space ID instead of dedicated param

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> Now that the address space ID is stored in every slot, including fake
> slots used for deletion, use the slot's as_id instead of passing in the
> redundant information as a param to kvm_set_memslot().  This will greatly
> simplify future memslot work by avoiding passing a large number of
> variables around purely to honor @as_id.
> 
> Drop a comment in the DELETE path about new->as_id being provided purely
> for debug, as that's now a lie.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

[PATCH v5.5 07/30] KVM: Let/force architectures to deal with arch specific memslot data

[Sean Christopherson]

Pass the "old" slot to kvm_arch_prepare_memory_region() and force arch
code to handle propagating arch specific data from "new" to "old" when
necessary.  This is a baby step towards dynamically allocating "new" from
the get go, and is a (very) minor performance boost on x86 due to not
unnecessarily copying arch data.

For PPC HV, copy the rmap in the !CREATE and !DELETE paths, i.e. for MOVE
and FLAGS_ONLY.  This is functionally a nop as the previous behavior
would overwrite the pointer for CREATE, and eventually discard/ignore it
for DELETE.

For x86, copy the arch data only for FLAGS_ONLY changes.  Unlike PPC HV,
x86 needs to reallocate arch data in the MOVE case as the size of x86's
allocations depend on the alignment of the memslot's gfn.

Opportunistically tweak kvm_arch_prepare_memory_region()'s param order to
match the "commit" prototype.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/arm64/kvm/mmu.c               |  7 ++++---
 arch/mips/kvm/mips.c               |  3 ++-
 arch/powerpc/include/asm/kvm_ppc.h | 18 ++++++++++--------
 arch/powerpc/kvm/book3s.c          | 12 ++++++------
 arch/powerpc/kvm/book3s_hv.c       | 17 ++++++++++-------
 arch/powerpc/kvm/book3s_pr.c       | 17 +++++++++--------
 arch/powerpc/kvm/booke.c           |  5 +++--
 arch/powerpc/kvm/powerpc.c         |  5 +++--
 arch/s390/kvm/kvm-s390.c           |  3 ++-
 arch/x86/kvm/x86.c                 | 15 +++++++++++----
 include/linux/kvm_host.h           |  3 ++-
 virt/kvm/kvm_main.c                |  5 +----
 12 files changed, 63 insertions(+), 47 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 69bd1732a299..cc41eadfbbf4 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1486,8 +1486,9 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 }
 
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
-				   struct kvm_memory_slot *memslot,
 				   const struct kvm_userspace_memory_region *mem,
+				   const struct kvm_memory_slot *old,
+				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
 {
 	hva_t hva = mem->userspace_addr;
@@ -1502,7 +1503,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	 * Prevent userspace from creating a memory region outside of the IPA
 	 * space addressable by the KVM guest IPA space.
 	 */
-	if ((memslot->base_gfn + memslot->npages) > (kvm_phys_size(kvm) >> PAGE_SHIFT))
+	if ((new->base_gfn + new->npages) > (kvm_phys_size(kvm) >> PAGE_SHIFT))
 		return -EFAULT;
 
 	mmap_read_lock(current->mm);
@@ -1536,7 +1537,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 
 		if (vma->vm_flags & VM_PFNMAP) {
 			/* IO region dirty page logging not allowed */
-			if (memslot->flags & KVM_MEM_LOG_DIRTY_PAGES) {
+			if (new->flags & KVM_MEM_LOG_DIRTY_PAGES) {
 				ret = -EINVAL;
 				break;
 			}
diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index 562aa878b266..8c94cd4093af 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -233,8 +233,9 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
 }
 
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
-				   struct kvm_memory_slot *memslot,
 				   const struct kvm_userspace_memory_region *mem,
+				   const struct kvm_memory_slot *old,
+				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
 {
 	return 0;
diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
index 671fbd1a765e..b01760dd1374 100644
--- a/arch/powerpc/include/asm/kvm_ppc.h
+++ b/arch/powerpc/include/asm/kvm_ppc.h
@@ -200,12 +200,13 @@ extern void kvmppc_core_destroy_vm(struct kvm *kvm);
 extern void kvmppc_core_free_memslot(struct kvm *kvm,
 				     struct kvm_memory_slot *slot);
 extern int kvmppc_core_prepare_memory_region(struct kvm *kvm,
-				struct kvm_memory_slot *memslot,
-				const struct kvm_userspace_memory_region *mem,
-				enum kvm_mr_change change);
-extern void kvmppc_core_commit_memory_region(struct kvm *kvm,
 				const struct kvm_userspace_memory_region *mem,
 				const struct kvm_memory_slot *old,
+				struct kvm_memory_slot *new,
+				enum kvm_mr_change change);
+extern void kvmppc_core_commit_memory_region(struct kvm *kvm,
+				const struct kvm_userspace_memory_region *mem,
+				struct kvm_memory_slot *old,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change);
 extern int kvm_vm_ioctl_get_smmu_info(struct kvm *kvm,
@@ -274,12 +275,13 @@ struct kvmppc_ops {
 	int (*get_dirty_log)(struct kvm *kvm, struct kvm_dirty_log *log);
 	void (*flush_memslot)(struct kvm *kvm, struct kvm_memory_slot *memslot);
 	int (*prepare_memory_region)(struct kvm *kvm,
-				     struct kvm_memory_slot *memslot,
-				     const struct kvm_userspace_memory_region *mem,
-				     enum kvm_mr_change change);
-	void (*commit_memory_region)(struct kvm *kvm,
 				     const struct kvm_userspace_memory_region *mem,
 				     const struct kvm_memory_slot *old,
+				     struct kvm_memory_slot *new,
+				     enum kvm_mr_change change);
+	void (*commit_memory_region)(struct kvm *kvm,
+				     const struct kvm_userspace_memory_region *mem,
+				     struct kvm_memory_slot *old,
 				     const struct kvm_memory_slot *new,
 				     enum kvm_mr_change change);
 	bool (*unmap_gfn_range)(struct kvm *kvm, struct kvm_gfn_range *range);
diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
index b785f6772391..8250e8308674 100644
--- a/arch/powerpc/kvm/book3s.c
+++ b/arch/powerpc/kvm/book3s.c
@@ -847,17 +847,17 @@ void kvmppc_core_flush_memslot(struct kvm *kvm, struct kvm_memory_slot *memslot)
 }
 
 int kvmppc_core_prepare_memory_region(struct kvm *kvm,
-				struct kvm_memory_slot *memslot,
-				const struct kvm_userspace_memory_region *mem,
-				enum kvm_mr_change change)
+				      const struct kvm_userspace_memory_region *mem,
+				      const struct kvm_memory_slot *old,
+				      struct kvm_memory_slot *new,
+				      enum kvm_mr_change change)
 {
-	return kvm->arch.kvm_ops->prepare_memory_region(kvm, memslot, mem,
-							change);
+	return kvm->arch.kvm_ops->prepare_memory_region(kvm, mem, old, new, change);
 }
 
 void kvmppc_core_commit_memory_region(struct kvm *kvm,
 				const struct kvm_userspace_memory_region *mem,
-				const struct kvm_memory_slot *old,
+				struct kvm_memory_slot *old,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
 {
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 2acb1c96cfaf..5bf763a74c22 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -4828,17 +4828,20 @@ static void kvmppc_core_free_memslot_hv(struct kvm_memory_slot *slot)
 }
 
 static int kvmppc_core_prepare_memory_region_hv(struct kvm *kvm,
-					struct kvm_memory_slot *slot,
-					const struct kvm_userspace_memory_region *mem,
-					enum kvm_mr_change change)
+				const struct kvm_userspace_memory_region *mem,
+				const struct kvm_memory_slot *old,
+				struct kvm_memory_slot *new,
+				enum kvm_mr_change change)
 {
 	unsigned long npages = mem->memory_size >> PAGE_SHIFT;
 
 	if (change == KVM_MR_CREATE) {
-		slot->arch.rmap = vzalloc(array_size(npages,
-					  sizeof(*slot->arch.rmap)));
-		if (!slot->arch.rmap)
+		new->arch.rmap = vzalloc(array_size(npages,
+					  sizeof(*new->arch.rmap)));
+		if (!new->arch.rmap)
 			return -ENOMEM;
+	} else if (change != KVM_MR_DELETE) {
+		new->arch.rmap = old->arch.rmap;
 	}
 
 	return 0;
@@ -4846,7 +4849,7 @@ static int kvmppc_core_prepare_memory_region_hv(struct kvm *kvm,
 
 static void kvmppc_core_commit_memory_region_hv(struct kvm *kvm,
 				const struct kvm_userspace_memory_region *mem,
-				const struct kvm_memory_slot *old,
+				struct kvm_memory_slot *old,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
 {
diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index 6bc9425acb32..58d3ae4605c0 100644
--- a/arch/powerpc/kvm/book3s_pr.c
+++ b/arch/powerpc/kvm/book3s_pr.c
@@ -1899,16 +1899,17 @@ static void kvmppc_core_flush_memslot_pr(struct kvm *kvm,
 }
 
 static int kvmppc_core_prepare_memory_region_pr(struct kvm *kvm,
-					struct kvm_memory_slot *memslot,
-					const struct kvm_userspace_memory_region *mem,
-					enum kvm_mr_change change)
-{
-	return 0;
-}
-
-static void kvmppc_core_commit_memory_region_pr(struct kvm *kvm,
 				const struct kvm_userspace_memory_region *mem,
 				const struct kvm_memory_slot *old,
+				struct kvm_memory_slot *new,
+				enum kvm_mr_change change)
+{
+	return 0;
+}
+
+static void kvmppc_core_commit_memory_region_pr(struct kvm *kvm,
+				const struct kvm_userspace_memory_region *mem,
+				struct kvm_memory_slot *old,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
 {
diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
index 977801c83aff..fcf9c1dbd442 100644
--- a/arch/powerpc/kvm/booke.c
+++ b/arch/powerpc/kvm/booke.c
@@ -1807,8 +1807,9 @@ void kvmppc_core_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
 }
 
 int kvmppc_core_prepare_memory_region(struct kvm *kvm,
-				      struct kvm_memory_slot *memslot,
 				      const struct kvm_userspace_memory_region *mem,
+				      const struct kvm_memory_slot *old,
+				      struct kvm_memory_slot *new,
 				      enum kvm_mr_change change)
 {
 	return 0;
@@ -1816,7 +1817,7 @@ int kvmppc_core_prepare_memory_region(struct kvm *kvm,
 
 void kvmppc_core_commit_memory_region(struct kvm *kvm,
 				const struct kvm_userspace_memory_region *mem,
-				const struct kvm_memory_slot *old,
+				struct kvm_memory_slot *old,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
 {
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 8ab90ce8738f..ca28e7acaae8 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -706,11 +706,12 @@ void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
 }
 
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
-				   struct kvm_memory_slot *memslot,
 				   const struct kvm_userspace_memory_region *mem,
+				   const struct kvm_memory_slot *old,
+				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
 {
-	return kvmppc_core_prepare_memory_region(kvm, memslot, mem, change);
+	return kvmppc_core_prepare_memory_region(kvm, mem, old, new, change);
 }
 
 void kvm_arch_commit_memory_region(struct kvm *kvm,
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 6a6dd5e1daf6..d766d764d24c 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -5016,8 +5016,9 @@ vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
 
 /* Section: memory related */
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
-				   struct kvm_memory_slot *memslot,
 				   const struct kvm_userspace_memory_region *mem,
+				   const struct kvm_memory_slot *old,
+				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
 {
 	/* A few sanity checks. We can have memory slots which have to be
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ac83d873d65b..aa2abca47af0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11727,13 +11727,20 @@ void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen)
 }
 
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
-				struct kvm_memory_slot *memslot,
-				const struct kvm_userspace_memory_region *mem,
-				enum kvm_mr_change change)
+				   const struct kvm_userspace_memory_region *mem,
+				   const struct kvm_memory_slot *old,
+				   struct kvm_memory_slot *new,
+				   enum kvm_mr_change change)
 {
 	if (change == KVM_MR_CREATE || change == KVM_MR_MOVE)
-		return kvm_alloc_memslot_metadata(kvm, memslot,
+		return kvm_alloc_memslot_metadata(kvm, new,
 						  mem->memory_size >> PAGE_SHIFT);
+
+	if (change == KVM_MR_FLAGS_ONLY)
+		memcpy(&new->arch, &old->arch, sizeof(old->arch));
+	else if (WARN_ON_ONCE(change != KVM_MR_DELETE))
+		return -EIO;
+
 	return 0;
 }
 
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index d8e92d4a78d8..f8e79cf7584f 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -826,8 +826,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
 void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot);
 void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen);
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
-				struct kvm_memory_slot *memslot,
 				const struct kvm_userspace_memory_region *mem,
+				const struct kvm_memory_slot *old,
+				struct kvm_memory_slot *new,
 				enum kvm_mr_change change);
 void kvm_arch_commit_memory_region(struct kvm *kvm,
 				const struct kvm_userspace_memory_region *mem,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 39a64e02a43a..389243120435 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1621,10 +1621,7 @@ static int kvm_set_memslot(struct kvm *kvm,
 		old.as_id = new->as_id;
 	}
 
-	/* Copy the arch-specific data, again after (re)acquiring slots_arch_lock. */
-	memcpy(&new->arch, &old.arch, sizeof(old.arch));
-
-	r = kvm_arch_prepare_memory_region(kvm, new, mem, change);
+	r = kvm_arch_prepare_memory_region(kvm, mem, &old, new, change);
 	if (r)
 		goto out_slots;
 
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 07/30] KVM: Let/force architectures to deal with arch specific memslot data

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> Pass the "old" slot to kvm_arch_prepare_memory_region() and force arch
> code to handle propagating arch specific data from "new" to "old" when
> necessary.  This is a baby step towards dynamically allocating "new" from
> the get go, and is a (very) minor performance boost on x86 due to not
> unnecessarily copying arch data.
> 
> For PPC HV, copy the rmap in the !CREATE and !DELETE paths, i.e. for MOVE
> and FLAGS_ONLY.  This is functionally a nop as the previous behavior
> would overwrite the pointer for CREATE, and eventually discard/ignore it
> for DELETE.
> 
> For x86, copy the arch data only for FLAGS_ONLY changes.  Unlike PPC HV,
> x86 needs to reallocate arch data in the MOVE case as the size of x86's
> allocations depend on the alignment of the memslot's gfn.
> 
> Opportunistically tweak kvm_arch_prepare_memory_region()'s param order to
> match the "commit" prototype.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   arch/arm64/kvm/mmu.c               |  7 ++++---
>   arch/mips/kvm/mips.c               |  3 ++-
>   arch/powerpc/include/asm/kvm_ppc.h | 18 ++++++++++--------
>   arch/powerpc/kvm/book3s.c          | 12 ++++++------
>   arch/powerpc/kvm/book3s_hv.c       | 17 ++++++++++-------
>   arch/powerpc/kvm/book3s_pr.c       | 17 +++++++++--------
>   arch/powerpc/kvm/booke.c           |  5 +++--
>   arch/powerpc/kvm/powerpc.c         |  5 +++--
>   arch/s390/kvm/kvm-s390.c           |  3 ++-
>   arch/x86/kvm/x86.c                 | 15 +++++++++++----
>   include/linux/kvm_host.h           |  3 ++-
>   virt/kvm/kvm_main.c                |  5 +----
>   12 files changed, 63 insertions(+), 47 deletions(-)
> 

You didn't include the RISCV kvm_arch_prepare_memory_region() change here
(that's actually in patch 13 of this series) so bisection on that arch
will be broken between this patch and patch 13.

Thanks,
Maciej

Re: [PATCH v5.5 07/30] KVM: Let/force architectures to deal with arch specific memslot data

[Sean Christopherson]

On Tue, Nov 09, 2021, Maciej S. Szmigiero wrote:
> On 04.11.2021 01:25, Sean Christopherson wrote:
> > Pass the "old" slot to kvm_arch_prepare_memory_region() and force arch
> > code to handle propagating arch specific data from "new" to "old" when
> > necessary.  This is a baby step towards dynamically allocating "new" from
> > the get go, and is a (very) minor performance boost on x86 due to not
> > unnecessarily copying arch data.
> > 
> > For PPC HV, copy the rmap in the !CREATE and !DELETE paths, i.e. for MOVE
> > and FLAGS_ONLY.  This is functionally a nop as the previous behavior
> > would overwrite the pointer for CREATE, and eventually discard/ignore it
> > for DELETE.
> > 
> > For x86, copy the arch data only for FLAGS_ONLY changes.  Unlike PPC HV,
> > x86 needs to reallocate arch data in the MOVE case as the size of x86's
> > allocations depend on the alignment of the memslot's gfn.
> > 
> > Opportunistically tweak kvm_arch_prepare_memory_region()'s param order to
> > match the "commit" prototype.
> > 
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > ---
> >   arch/arm64/kvm/mmu.c               |  7 ++++---
> >   arch/mips/kvm/mips.c               |  3 ++-
> >   arch/powerpc/include/asm/kvm_ppc.h | 18 ++++++++++--------
> >   arch/powerpc/kvm/book3s.c          | 12 ++++++------
> >   arch/powerpc/kvm/book3s_hv.c       | 17 ++++++++++-------
> >   arch/powerpc/kvm/book3s_pr.c       | 17 +++++++++--------
> >   arch/powerpc/kvm/booke.c           |  5 +++--
> >   arch/powerpc/kvm/powerpc.c         |  5 +++--
> >   arch/s390/kvm/kvm-s390.c           |  3 ++-
> >   arch/x86/kvm/x86.c                 | 15 +++++++++++----
> >   include/linux/kvm_host.h           |  3 ++-
> >   virt/kvm/kvm_main.c                |  5 +----
> >   12 files changed, 63 insertions(+), 47 deletions(-)
> > 
> 
> You didn't include the RISCV kvm_arch_prepare_memory_region() change here
> (that's actually in patch 13 of this series) so bisection on that arch
> will be broken between this patch and patch 13.

Argh, I thought I had found all of those.  :-/  Thanks.  

[PATCH v5.5 08/30] KVM: arm64: Use "new" memslot instead of userspace memory region

[Sean Christopherson]

Get the slot ID, hva, etc... from the "new" memslot instead of the
userspace memory region when preparing/committing a memory region.  This
will allow a future commit to drop @mem from the prepare/commit hooks
once all architectures convert to using "new".

Opportunistically wait to get the hva begin+end until after filtering out
the DELETE case in anticipation of a future commit passing NULL for @new
when deleting a memslot.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/arm64/kvm/mmu.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index cc41eadfbbf4..21213cba7c47 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1473,14 +1473,14 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 	 * allocated dirty_bitmap[], dirty pages will be tracked while the
 	 * memory slot is write protected.
 	 */
-	if (change != KVM_MR_DELETE && mem->flags & KVM_MEM_LOG_DIRTY_PAGES) {
+	if (change != KVM_MR_DELETE && new->flags & KVM_MEM_LOG_DIRTY_PAGES) {
 		/*
 		 * If we're with initial-all-set, we don't need to write
 		 * protect any pages because they're all reported as dirty.
 		 * Huge pages and normal pages will be write protect gradually.
 		 */
 		if (!kvm_dirty_log_manual_protect_and_init_set(kvm)) {
-			kvm_mmu_wp_memory_region(kvm, mem->slot);
+			kvm_mmu_wp_memory_region(kvm, new->id);
 		}
 	}
 }
@@ -1491,8 +1491,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
 {
-	hva_t hva = mem->userspace_addr;
-	hva_t reg_end = hva + mem->memory_size;
+	hva_t hva, reg_end;
 	int ret = 0;
 
 	if (change != KVM_MR_CREATE && change != KVM_MR_MOVE &&
@@ -1506,6 +1505,9 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	if ((new->base_gfn + new->npages) > (kvm_phys_size(kvm) >> PAGE_SHIFT))
 		return -EFAULT;
 
+	hva = new->userspace_addr;
+	reg_end = hva + (new->npages << PAGE_SHIFT);
+
 	mmap_read_lock(current->mm);
 	/*
 	 * A memory region could potentially cover multiple VMAs, and any holes
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 08/30] KVM: arm64: Use "new" memslot instead of userspace memory region

[Reiji Watanabe]

On Wed, Nov 3, 2021 at 5:26 PM Sean Christopherson <seanjc@google.com> wrote:
>
> Get the slot ID, hva, etc... from the "new" memslot instead of the
> userspace memory region when preparing/committing a memory region.  This
> will allow a future commit to drop @mem from the prepare/commit hooks
> once all architectures convert to using "new".
>
> Opportunistically wait to get the hva begin+end until after filtering out
> the DELETE case in anticipation of a future commit passing NULL for @new
> when deleting a memslot.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Reiji Watanabe <reijiw@google.com>

[PATCH v5.5 09/30] KVM: MIPS: Drop pr_debug from memslot commit to avoid using "mem"

[Sean Christopherson]

Remove an old (circa 2012) kvm_debug from kvm_arch_commit_memory_region()
to print basic information when committing a memslot change.  The primary
motivation for removing the kvm_debug is to avoid using @mem, the user
memory region, so that said param can be removed.

Alternatively, the debug message could be converted to use @new, but that
would require synthesizing select state to play nice with the DELETED
case, which will pass NULL for @new in the future.  And there's no
argument to be had for dumping generic information in an arch callback,
i.e. if there's a good reason for the debug message, then it belongs in
common KVM code where all architectures can benefit.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/mips/kvm/mips.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index 8c94cd4093af..b7aa8fa4a5fb 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -249,10 +249,6 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 {
 	int needs_flush;
 
-	kvm_debug("%s: kvm: %p slot: %d, GPA: %llx, size: %llx, QVA: %llx\n",
-		  __func__, kvm, mem->slot, mem->guest_phys_addr,
-		  mem->memory_size, mem->userspace_addr);
-
 	/*
 	 * If dirty page logging is enabled, write protect all pages in the slot
 	 * ready for dirty logging.
-- 
2.33.1.1089.g2158813163f-goog

[PATCH v5.5 10/30] KVM: PPC: Avoid referencing userspace memory region in memslot updates

[Sean Christopherson]

For PPC HV, get the number of pages directly from the new memslot instead
of computing the same from the userspace memory region, and explicitly
check for !DELETE instead of inferring the same when toggling mmio_update.
The motivation for these changes is to avoid referencing the @mem param
so that it can be dropped in a future commit.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/powerpc/include/asm/kvm_ppc.h |  4 ----
 arch/powerpc/kvm/book3s.c          |  6 ++----
 arch/powerpc/kvm/book3s_hv.c       | 12 +++---------
 arch/powerpc/kvm/book3s_pr.c       |  2 --
 arch/powerpc/kvm/booke.c           |  2 --
 arch/powerpc/kvm/powerpc.c         |  4 ++--
 6 files changed, 7 insertions(+), 23 deletions(-)

diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
index b01760dd1374..935c58dc38c4 100644
--- a/arch/powerpc/include/asm/kvm_ppc.h
+++ b/arch/powerpc/include/asm/kvm_ppc.h
@@ -200,12 +200,10 @@ extern void kvmppc_core_destroy_vm(struct kvm *kvm);
 extern void kvmppc_core_free_memslot(struct kvm *kvm,
 				     struct kvm_memory_slot *slot);
 extern int kvmppc_core_prepare_memory_region(struct kvm *kvm,
-				const struct kvm_userspace_memory_region *mem,
 				const struct kvm_memory_slot *old,
 				struct kvm_memory_slot *new,
 				enum kvm_mr_change change);
 extern void kvmppc_core_commit_memory_region(struct kvm *kvm,
-				const struct kvm_userspace_memory_region *mem,
 				struct kvm_memory_slot *old,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change);
@@ -275,12 +273,10 @@ struct kvmppc_ops {
 	int (*get_dirty_log)(struct kvm *kvm, struct kvm_dirty_log *log);
 	void (*flush_memslot)(struct kvm *kvm, struct kvm_memory_slot *memslot);
 	int (*prepare_memory_region)(struct kvm *kvm,
-				     const struct kvm_userspace_memory_region *mem,
 				     const struct kvm_memory_slot *old,
 				     struct kvm_memory_slot *new,
 				     enum kvm_mr_change change);
 	void (*commit_memory_region)(struct kvm *kvm,
-				     const struct kvm_userspace_memory_region *mem,
 				     struct kvm_memory_slot *old,
 				     const struct kvm_memory_slot *new,
 				     enum kvm_mr_change change);
diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
index 8250e8308674..6d525285dbe8 100644
--- a/arch/powerpc/kvm/book3s.c
+++ b/arch/powerpc/kvm/book3s.c
@@ -847,21 +847,19 @@ void kvmppc_core_flush_memslot(struct kvm *kvm, struct kvm_memory_slot *memslot)
 }
 
 int kvmppc_core_prepare_memory_region(struct kvm *kvm,
-				      const struct kvm_userspace_memory_region *mem,
 				      const struct kvm_memory_slot *old,
 				      struct kvm_memory_slot *new,
 				      enum kvm_mr_change change)
 {
-	return kvm->arch.kvm_ops->prepare_memory_region(kvm, mem, old, new, change);
+	return kvm->arch.kvm_ops->prepare_memory_region(kvm, old, new, change);
 }
 
 void kvmppc_core_commit_memory_region(struct kvm *kvm,
-				const struct kvm_userspace_memory_region *mem,
 				struct kvm_memory_slot *old,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
 {
-	kvm->arch.kvm_ops->commit_memory_region(kvm, mem, old, new, change);
+	kvm->arch.kvm_ops->commit_memory_region(kvm, old, new, change);
 }
 
 bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 5bf763a74c22..4d40c1867be5 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -4828,15 +4828,12 @@ static void kvmppc_core_free_memslot_hv(struct kvm_memory_slot *slot)
 }
 
 static int kvmppc_core_prepare_memory_region_hv(struct kvm *kvm,
-				const struct kvm_userspace_memory_region *mem,
 				const struct kvm_memory_slot *old,
 				struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
 {
-	unsigned long npages = mem->memory_size >> PAGE_SHIFT;
-
 	if (change == KVM_MR_CREATE) {
-		new->arch.rmap = vzalloc(array_size(npages,
+		new->arch.rmap = vzalloc(array_size(new->npages,
 					  sizeof(*new->arch.rmap)));
 		if (!new->arch.rmap)
 			return -ENOMEM;
@@ -4848,20 +4845,17 @@ static int kvmppc_core_prepare_memory_region_hv(struct kvm *kvm,
 }
 
 static void kvmppc_core_commit_memory_region_hv(struct kvm *kvm,
-				const struct kvm_userspace_memory_region *mem,
 				struct kvm_memory_slot *old,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
 {
-	unsigned long npages = mem->memory_size >> PAGE_SHIFT;
-
 	/*
-	 * If we are making a new memslot, it might make
+	 * If we are creating or modifying a memslot, it might make
 	 * some address that was previously cached as emulated
 	 * MMIO be no longer emulated MMIO, so invalidate
 	 * all the caches of emulated MMIO translations.
 	 */
-	if (npages)
+	if (change != KVM_MR_DELETE)
 		atomic64_inc(&kvm->arch.mmio_update);
 
 	/*
diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index 58d3ae4605c0..ca3bfba94fe4 100644
--- a/arch/powerpc/kvm/book3s_pr.c
+++ b/arch/powerpc/kvm/book3s_pr.c
@@ -1899,7 +1899,6 @@ static void kvmppc_core_flush_memslot_pr(struct kvm *kvm,
 }
 
 static int kvmppc_core_prepare_memory_region_pr(struct kvm *kvm,
-				const struct kvm_userspace_memory_region *mem,
 				const struct kvm_memory_slot *old,
 				struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
@@ -1908,7 +1907,6 @@ static int kvmppc_core_prepare_memory_region_pr(struct kvm *kvm,
 }
 
 static void kvmppc_core_commit_memory_region_pr(struct kvm *kvm,
-				const struct kvm_userspace_memory_region *mem,
 				struct kvm_memory_slot *old,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
index fcf9c1dbd442..25dcf079c713 100644
--- a/arch/powerpc/kvm/booke.c
+++ b/arch/powerpc/kvm/booke.c
@@ -1807,7 +1807,6 @@ void kvmppc_core_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
 }
 
 int kvmppc_core_prepare_memory_region(struct kvm *kvm,
-				      const struct kvm_userspace_memory_region *mem,
 				      const struct kvm_memory_slot *old,
 				      struct kvm_memory_slot *new,
 				      enum kvm_mr_change change)
@@ -1816,7 +1815,6 @@ int kvmppc_core_prepare_memory_region(struct kvm *kvm,
 }
 
 void kvmppc_core_commit_memory_region(struct kvm *kvm,
-				const struct kvm_userspace_memory_region *mem,
 				struct kvm_memory_slot *old,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index ca28e7acaae8..59342237e046 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -711,7 +711,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
 {
-	return kvmppc_core_prepare_memory_region(kvm, mem, old, new, change);
+	return kvmppc_core_prepare_memory_region(kvm, old, new, change);
 }
 
 void kvm_arch_commit_memory_region(struct kvm *kvm,
@@ -720,7 +720,7 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 				   const struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
 {
-	kvmppc_core_commit_memory_region(kvm, mem, old, new, change);
+	kvmppc_core_commit_memory_region(kvm, old, new, change);
 }
 
 void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
-- 
2.33.1.1089.g2158813163f-goog

[PATCH v5.5 11/30] KVM: s390: Use "new" memslot instead of userspace memory region

[Sean Christopherson]

Get the gfn, size, and hva from the new memslot instead of the userspace
memory region when preparing/committing memory region changes.  This will
allow a future commit to drop the @mem param.

Note, this has a subtle functional change as KVM would previously reject
DELETE if userspace provided a garbage userspace_addr or guest_phys_addr,
whereas KVM zeros those fields in the "new" memslot when deleting an
existing memslot.  Arguably the old behavior is more correct, but there's
zero benefit into requiring userspace to provide sane values for hva and
gfn.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---

If we want to keep the checks for DELETE, my vote would be to add an
arch hook that is dedicated to validated the userspace memory region
so that the prepare/commit hooks operate only on KVM-generate objects.

 arch/s390/kvm/kvm-s390.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index d766d764d24c..e69ad13612d9 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -5021,18 +5021,20 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
 {
+	gpa_t size = new->npages * PAGE_SIZE;
+
 	/* A few sanity checks. We can have memory slots which have to be
 	   located/ended at a segment boundary (1MB). The memory in userland is
 	   ok to be fragmented into various different vmas. It is okay to mmap()
 	   and munmap() stuff in this slot after doing this call at any time */
 
-	if (mem->userspace_addr & 0xffffful)
+	if (new->userspace_addr & 0xffffful)
 		return -EINVAL;
 
-	if (mem->memory_size & 0xffffful)
+	if (size & 0xffffful)
 		return -EINVAL;
 
-	if (mem->guest_phys_addr + mem->memory_size > kvm->arch.mem_limit)
+	if ((new->base_gfn * PAGE_SIZE) + size > kvm->arch.mem_limit)
 		return -EINVAL;
 
 	/* When we are protected, we should not change the memory slots */
@@ -5061,8 +5063,9 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 			break;
 		fallthrough;
 	case KVM_MR_CREATE:
-		rc = gmap_map_segment(kvm->arch.gmap, mem->userspace_addr,
-				      mem->guest_phys_addr, mem->memory_size);
+		rc = gmap_map_segment(kvm->arch.gmap, new->userspace_addr,
+				      new->base_gfn * PAGE_SIZE,
+				      new->npages * PAGE_SIZE);
 		break;
 	case KVM_MR_FLAGS_ONLY:
 		break;
-- 
2.33.1.1089.g2158813163f-goog

[PATCH v5.5 12/30] KVM: x86: Use "new" memslot instead of userspace memory region

[Sean Christopherson]

Get the number of pages directly from the new memslot instead of
computing the same from the userspace memory region when allocating
memslot metadata.  This will allow a future patch to drop @mem.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/x86.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index aa2abca47af0..c68e7de9f116 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11646,9 +11646,9 @@ int memslot_rmap_alloc(struct kvm_memory_slot *slot, unsigned long npages)
 }
 
 static int kvm_alloc_memslot_metadata(struct kvm *kvm,
-				      struct kvm_memory_slot *slot,
-				      unsigned long npages)
+				      struct kvm_memory_slot *slot)
 {
+	unsigned long npages = slot->npages;
 	int i, r;
 
 	/*
@@ -11733,8 +11733,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 				   enum kvm_mr_change change)
 {
 	if (change == KVM_MR_CREATE || change == KVM_MR_MOVE)
-		return kvm_alloc_memslot_metadata(kvm, new,
-						  mem->memory_size >> PAGE_SHIFT);
+		return kvm_alloc_memslot_metadata(kvm, new);
 
 	if (change == KVM_MR_FLAGS_ONLY)
 		memcpy(&new->arch, &old->arch, sizeof(old->arch));
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 12/30] KVM: x86: Use "new" memslot instead of userspace memory region

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> Get the number of pages directly from the new memslot instead of
> computing the same from the userspace memory region when allocating
> memslot metadata.  This will allow a future patch to drop @mem.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

[PATCH v5.5 13/30] KVM: RISC-V: Use "new" memslot instead of userspace memory region

[Sean Christopherson]

Get the slot ID, hva, etc... from the "new" memslot instead of the
userspace memory region when preparing/committing a memory region.  This
will allow a future commit to drop @mem from the prepare/commit hooks
once all architectures convert to using "new".

Opportunistically wait to get the various "new" values until after
filtering out the DELETE case in anticipation of a future commit passing
NULL for @new when deleting a memslot.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/riscv/kvm/mmu.c | 34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
index 3a00c2df7640..db5230ec6951 100644
--- a/arch/riscv/kvm/mmu.c
+++ b/arch/riscv/kvm/mmu.c
@@ -466,18 +466,19 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 	 * allocated dirty_bitmap[], dirty pages will be tracked while
 	 * the memory slot is write protected.
 	 */
-	if (change != KVM_MR_DELETE && mem->flags & KVM_MEM_LOG_DIRTY_PAGES)
-		stage2_wp_memory_region(kvm, mem->slot);
+	if (change != KVM_MR_DELETE && new->flags & KVM_MEM_LOG_DIRTY_PAGES)
+		stage2_wp_memory_region(kvm, new->id);
 }
 
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
-				struct kvm_memory_slot *memslot,
-				const struct kvm_userspace_memory_region *mem,
-				enum kvm_mr_change change)
+				   const struct kvm_userspace_memory_region *mem,
+				   const struct kvm_memory_slot *old,
+				   struct kvm_memory_slot *new,
+				   enum kvm_mr_change change)
 {
-	hva_t hva = mem->userspace_addr;
-	hva_t reg_end = hva + mem->memory_size;
-	bool writable = !(mem->flags & KVM_MEM_READONLY);
+	hva_t hva, reg_end, size;
+	gpa_t base_gpa;
+	bool writable;
 	int ret = 0;
 
 	if (change != KVM_MR_CREATE && change != KVM_MR_MOVE &&
@@ -488,10 +489,15 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	 * Prevent userspace from creating a memory region outside of the GPA
 	 * space addressable by the KVM guest GPA space.
 	 */
-	if ((memslot->base_gfn + memslot->npages) >=
-	    (stage2_gpa_size >> PAGE_SHIFT))
+	if ((new->base_gfn + new->npages) >= (stage2_gpa_size >> PAGE_SHIFT))
 		return -EFAULT;
 
+	hva = new->userspace_addr;
+	size = new->npages << PAGE_SHIFT;
+	reg_end = hva + size;
+	base_gpa = new->base_gfn << PAGE_SHIFT;
+	writable = !(new->flags & KVM_MEM_READONLY);
+
 	mmap_read_lock(current->mm);
 
 	/*
@@ -527,15 +533,14 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 		vm_end = min(reg_end, vma->vm_end);
 
 		if (vma->vm_flags & VM_PFNMAP) {
-			gpa_t gpa = mem->guest_phys_addr +
-				    (vm_start - mem->userspace_addr);
+			gpa_t gpa = base_gpa + (vm_start - hva);
 			phys_addr_t pa;
 
 			pa = (phys_addr_t)vma->vm_pgoff << PAGE_SHIFT;
 			pa += vm_start - vma->vm_start;
 
 			/* IO region dirty page logging not allowed */
-			if (memslot->flags & KVM_MEM_LOG_DIRTY_PAGES) {
+			if (new->flags & KVM_MEM_LOG_DIRTY_PAGES) {
 				ret = -EINVAL;
 				goto out;
 			}
@@ -553,8 +558,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 
 	spin_lock(&kvm->mmu_lock);
 	if (ret)
-		stage2_unmap_range(kvm, mem->guest_phys_addr,
-				   mem->memory_size, false);
+		stage2_unmap_range(kvm, base_gpa, size, false);
 	spin_unlock(&kvm->mmu_lock);
 
 out:
-- 
2.33.1.1089.g2158813163f-goog

[PATCH v5.5 14/30] KVM: Stop passing kvm_userspace_memory_region to arch memslot hooks

[Sean Christopherson]

Drop the @mem param from kvm_arch_{prepare,commit}_memory_region() now
that its use has been removed in all architectures.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/arm64/kvm/mmu.c       | 2 --
 arch/mips/kvm/mips.c       | 2 --
 arch/powerpc/kvm/powerpc.c | 2 --
 arch/riscv/kvm/mmu.c       | 2 --
 arch/s390/kvm/kvm-s390.c   | 2 --
 arch/x86/kvm/x86.c         | 2 --
 include/linux/kvm_host.h   | 2 --
 virt/kvm/kvm_main.c        | 9 ++++-----
 8 files changed, 4 insertions(+), 19 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 21213cba7c47..a76718388cbd 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1463,7 +1463,6 @@ int kvm_mmu_init(u32 *hyp_va_bits)
 }
 
 void kvm_arch_commit_memory_region(struct kvm *kvm,
-				   const struct kvm_userspace_memory_region *mem,
 				   struct kvm_memory_slot *old,
 				   const struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
@@ -1486,7 +1485,6 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 }
 
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
-				   const struct kvm_userspace_memory_region *mem,
 				   const struct kvm_memory_slot *old,
 				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index b7aa8fa4a5fb..47b7dc149032 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -233,7 +233,6 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
 }
 
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
-				   const struct kvm_userspace_memory_region *mem,
 				   const struct kvm_memory_slot *old,
 				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
@@ -242,7 +241,6 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 }
 
 void kvm_arch_commit_memory_region(struct kvm *kvm,
-				   const struct kvm_userspace_memory_region *mem,
 				   struct kvm_memory_slot *old,
 				   const struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 59342237e046..52ab1782b257 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -706,7 +706,6 @@ void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
 }
 
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
-				   const struct kvm_userspace_memory_region *mem,
 				   const struct kvm_memory_slot *old,
 				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
@@ -715,7 +714,6 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 }
 
 void kvm_arch_commit_memory_region(struct kvm *kvm,
-				   const struct kvm_userspace_memory_region *mem,
 				   struct kvm_memory_slot *old,
 				   const struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
index db5230ec6951..0732867d398c 100644
--- a/arch/riscv/kvm/mmu.c
+++ b/arch/riscv/kvm/mmu.c
@@ -456,7 +456,6 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
 }
 
 void kvm_arch_commit_memory_region(struct kvm *kvm,
-				const struct kvm_userspace_memory_region *mem,
 				struct kvm_memory_slot *old,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
@@ -471,7 +470,6 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 }
 
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
-				   const struct kvm_userspace_memory_region *mem,
 				   const struct kvm_memory_slot *old,
 				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index e69ad13612d9..81f90891db0f 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -5016,7 +5016,6 @@ vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
 
 /* Section: memory related */
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
-				   const struct kvm_userspace_memory_region *mem,
 				   const struct kvm_memory_slot *old,
 				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
@@ -5044,7 +5043,6 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 }
 
 void kvm_arch_commit_memory_region(struct kvm *kvm,
-				const struct kvm_userspace_memory_region *mem,
 				struct kvm_memory_slot *old,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c68e7de9f116..80e726f73dd7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11727,7 +11727,6 @@ void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen)
 }
 
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
-				   const struct kvm_userspace_memory_region *mem,
 				   const struct kvm_memory_slot *old,
 				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
@@ -11831,7 +11830,6 @@ static void kvm_mmu_slot_apply_flags(struct kvm *kvm,
 }
 
 void kvm_arch_commit_memory_region(struct kvm *kvm,
-				const struct kvm_userspace_memory_region *mem,
 				struct kvm_memory_slot *old,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index f8e79cf7584f..2ef946e94a73 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -826,12 +826,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
 void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot);
 void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen);
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
-				const struct kvm_userspace_memory_region *mem,
 				const struct kvm_memory_slot *old,
 				struct kvm_memory_slot *new,
 				enum kvm_mr_change change);
 void kvm_arch_commit_memory_region(struct kvm *kvm,
-				const struct kvm_userspace_memory_region *mem,
 				struct kvm_memory_slot *old,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 389243120435..9c75691b98ba 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1535,7 +1535,6 @@ static void kvm_copy_memslots_arch(struct kvm_memslots *to,
 }
 
 static int kvm_set_memslot(struct kvm *kvm,
-			   const struct kvm_userspace_memory_region *mem,
 			   struct kvm_memory_slot *new,
 			   enum kvm_mr_change change)
 {
@@ -1621,7 +1620,7 @@ static int kvm_set_memslot(struct kvm *kvm,
 		old.as_id = new->as_id;
 	}
 
-	r = kvm_arch_prepare_memory_region(kvm, mem, &old, new, change);
+	r = kvm_arch_prepare_memory_region(kvm, &old, new, change);
 	if (r)
 		goto out_slots;
 
@@ -1637,7 +1636,7 @@ static int kvm_set_memslot(struct kvm *kvm,
 	else if (change == KVM_MR_CREATE)
 		kvm->nr_memslot_pages += new->npages;
 
-	kvm_arch_commit_memory_region(kvm, mem, &old, new, change);
+	kvm_arch_commit_memory_region(kvm, &old, new, change);
 
 	/* Free the old memslot's metadata.  Note, this is the full copy!!! */
 	if (change == KVM_MR_DELETE)
@@ -1722,7 +1721,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		new.id = id;
 		new.as_id = as_id;
 
-		return kvm_set_memslot(kvm, mem, &new, KVM_MR_DELETE);
+		return kvm_set_memslot(kvm, &new, KVM_MR_DELETE);
 	}
 
 	new.as_id = as_id;
@@ -1785,7 +1784,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			bitmap_set(new.dirty_bitmap, 0, new.npages);
 	}
 
-	r = kvm_set_memslot(kvm, mem, &new, change);
+	r = kvm_set_memslot(kvm, &new, change);
 	if (r)
 		goto out_bitmap;
 
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 14/30] KVM: Stop passing kvm_userspace_memory_region to arch memslot hooks

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> Drop the @mem param from kvm_arch_{prepare,commit}_memory_region() now
> that its use has been removed in all architectures.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

[PATCH v5.5 15/30] KVM: Use prepare/commit hooks to handle generic memslot metadata updates

[Sean Christopherson]

Handle the generic memslot metadata, a.k.a. dirty bitmap, updates at the
same time that arch handles it's own metadata updates, i.e. at memslot
prepare and commit.  This will simplify converting @new to a dynamically
allocated object, and more closely aligns common KVM with architecture
code.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 virt/kvm/kvm_main.c | 109 +++++++++++++++++++++++++++-----------------
 1 file changed, 66 insertions(+), 43 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 9c75691b98ba..6c7bbc452dae 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1534,6 +1534,69 @@ static void kvm_copy_memslots_arch(struct kvm_memslots *to,
 		to->memslots[i].arch = from->memslots[i].arch;
 }
 
+static int kvm_prepare_memory_region(struct kvm *kvm,
+				     const struct kvm_memory_slot *old,
+				     struct kvm_memory_slot *new,
+				     enum kvm_mr_change change)
+{
+	int r;
+
+	/*
+	 * If dirty logging is disabled, nullify the bitmap; the old bitmap
+	 * will be freed on "commit".  If logging is enabled in both old and
+	 * new, reuse the existing bitmap.  If logging is enabled only in the
+	 * new and KVM isn't using a ring buffer, allocate and initialize a
+	 * new bitmap.
+	 */
+	if (!(new->flags & KVM_MEM_LOG_DIRTY_PAGES))
+		new->dirty_bitmap = NULL;
+	else if (old->dirty_bitmap)
+		new->dirty_bitmap = old->dirty_bitmap;
+	else if (!kvm->dirty_ring_size) {
+		r = kvm_alloc_dirty_bitmap(new);
+		if (r)
+			return r;
+
+		if (kvm_dirty_log_manual_protect_and_init_set(kvm))
+			bitmap_set(new->dirty_bitmap, 0, new->npages);
+	}
+
+	r = kvm_arch_prepare_memory_region(kvm, old, new, change);
+
+	/* Free the bitmap on failure if it was allocated above. */
+	if (r && new->dirty_bitmap && !old->dirty_bitmap)
+		kvm_destroy_dirty_bitmap(new);
+
+	return r;
+}
+
+static void kvm_commit_memory_region(struct kvm *kvm,
+				     struct kvm_memory_slot *old,
+				     const struct kvm_memory_slot *new,
+				     enum kvm_mr_change change)
+{
+	/*
+	 * Update the total number of memslot pages before calling the arch
+	 * hook so that architectures can consume the result directly.
+	 */
+	if (change == KVM_MR_DELETE)
+		kvm->nr_memslot_pages -= old->npages;
+	else if (change == KVM_MR_CREATE)
+		kvm->nr_memslot_pages += new->npages;
+
+	kvm_arch_commit_memory_region(kvm, old, new, change);
+
+	/*
+	 * Free the old memslot's metadata.  On DELETE, free the whole thing,
+	 * otherwise free the dirty bitmap as needed (the below effectively
+	 * checks both the flags and whether a ring buffer is being used).
+	 */
+	if (change == KVM_MR_DELETE)
+		kvm_free_memslot(kvm, old);
+	else if (old->dirty_bitmap && !new->dirty_bitmap)
+		kvm_destroy_dirty_bitmap(old);
+}
+
 static int kvm_set_memslot(struct kvm *kvm,
 			   struct kvm_memory_slot *new,
 			   enum kvm_mr_change change)
@@ -1620,27 +1683,14 @@ static int kvm_set_memslot(struct kvm *kvm,
 		old.as_id = new->as_id;
 	}
 
-	r = kvm_arch_prepare_memory_region(kvm, &old, new, change);
+	r = kvm_prepare_memory_region(kvm, &old, new, change);
 	if (r)
 		goto out_slots;
 
 	update_memslots(slots, new, change);
 	slots = install_new_memslots(kvm, new->as_id, slots);
 
-	/*
-	 * Update the total number of memslot pages before calling the arch
-	 * hook so that architectures can consume the result directly.
-	 */
-	if (change == KVM_MR_DELETE)
-		kvm->nr_memslot_pages -= old.npages;
-	else if (change == KVM_MR_CREATE)
-		kvm->nr_memslot_pages += new->npages;
-
-	kvm_arch_commit_memory_region(kvm, &old, new, change);
-
-	/* Free the old memslot's metadata.  Note, this is the full copy!!! */
-	if (change == KVM_MR_DELETE)
-		kvm_free_memslot(kvm, &old);
+	kvm_commit_memory_region(kvm, &old, new, change);
 
 	kvfree(slots);
 	return 0;
@@ -1736,7 +1786,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
 
 	if (!old.npages) {
 		change = KVM_MR_CREATE;
-		new.dirty_bitmap = NULL;
 
 		/*
 		 * To simplify KVM internals, the total number of pages across
@@ -1756,9 +1805,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			change = KVM_MR_FLAGS_ONLY;
 		else /* Nothing to change. */
 			return 0;
-
-		/* Copy dirty_bitmap from the current memslot. */
-		new.dirty_bitmap = old.dirty_bitmap;
 	}
 
 	if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
@@ -1772,30 +1818,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		}
 	}
 
-	/* Allocate/free page dirty bitmap as needed */
-	if (!(new.flags & KVM_MEM_LOG_DIRTY_PAGES))
-		new.dirty_bitmap = NULL;
-	else if (!new.dirty_bitmap && !kvm->dirty_ring_size) {
-		r = kvm_alloc_dirty_bitmap(&new);
-		if (r)
-			return r;
-
-		if (kvm_dirty_log_manual_protect_and_init_set(kvm))
-			bitmap_set(new.dirty_bitmap, 0, new.npages);
-	}
-
-	r = kvm_set_memslot(kvm, &new, change);
-	if (r)
-		goto out_bitmap;
-
-	if (old.dirty_bitmap && !new.dirty_bitmap)
-		kvm_destroy_dirty_bitmap(&old);
-	return 0;
-
-out_bitmap:
-	if (new.dirty_bitmap && !old.dirty_bitmap)
-		kvm_destroy_dirty_bitmap(&new);
-	return r;
+	return kvm_set_memslot(kvm, &new, change);
 }
 EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
 
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 15/30] KVM: Use prepare/commit hooks to handle generic memslot metadata updates

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> Handle the generic memslot metadata, a.k.a. dirty bitmap, updates at the
> same time that arch handles it's own metadata updates, i.e. at memslot
> prepare and commit.  This will simplify converting @new to a dynamically
> allocated object, and more closely aligns common KVM with architecture
> code.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

[PATCH v5.5 16/30] KVM: x86: Don't assume old/new memslots are non-NULL at memslot commit

[Sean Christopherson]

Play nice with a NULL @old or @new when handling memslot updates so that
common KVM can pass NULL for one or the other in CREATE and DELETE cases
instead of having to synthesize a dummy memslot.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/x86.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 80e726f73dd7..80183f7eadeb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11762,13 +11762,15 @@ static void kvm_mmu_slot_apply_flags(struct kvm *kvm,
 				     const struct kvm_memory_slot *new,
 				     enum kvm_mr_change change)
 {
-	bool log_dirty_pages = new->flags & KVM_MEM_LOG_DIRTY_PAGES;
+	u32 old_flags = old ? old->flags : 0;
+	u32 new_flags = new ? new->flags : 0;
+	bool log_dirty_pages = new_flags & KVM_MEM_LOG_DIRTY_PAGES;
 
 	/*
 	 * Update CPU dirty logging if dirty logging is being toggled.  This
 	 * applies to all operations.
 	 */
-	if ((old->flags ^ new->flags) & KVM_MEM_LOG_DIRTY_PAGES)
+	if ((old_flags ^ new_flags) & KVM_MEM_LOG_DIRTY_PAGES)
 		kvm_mmu_update_cpu_dirty_logging(kvm, log_dirty_pages);
 
 	/*
@@ -11786,7 +11788,7 @@ static void kvm_mmu_slot_apply_flags(struct kvm *kvm,
 	 * MOVE/DELETE: The old mappings will already have been cleaned up by
 	 *		kvm_arch_flush_shadow_memslot().
 	 */
-	if ((change != KVM_MR_FLAGS_ONLY) || (new->flags & KVM_MEM_READONLY))
+	if ((change != KVM_MR_FLAGS_ONLY) || (new_flags & KVM_MEM_READONLY))
 		return;
 
 	/*
@@ -11794,7 +11796,7 @@ static void kvm_mmu_slot_apply_flags(struct kvm *kvm,
 	 * other flag is LOG_DIRTY_PAGES, i.e. something is wrong if dirty
 	 * logging isn't being toggled on or off.
 	 */
-	if (WARN_ON_ONCE(!((old->flags ^ new->flags) & KVM_MEM_LOG_DIRTY_PAGES)))
+	if (WARN_ON_ONCE(!((old_flags ^ new_flags) & KVM_MEM_LOG_DIRTY_PAGES)))
 		return;
 
 	if (!log_dirty_pages) {
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 16/30] KVM: x86: Don't assume old/new memslots are non-NULL at memslot commit

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> Play nice with a NULL @old or @new when handling memslot updates so that
> common KVM can pass NULL for one or the other in CREATE and DELETE cases
> instead of having to synthesize a dummy memslot.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

[PATCH v5.5 17/30] KVM: s390: Skip gfn/size sanity checks on memslot DELETE or FLAGS_ONLY

[Sean Christopherson]

Sanity check the hva, gfn, and size of a userspace memory region only if
any of those properties can change, i.e. skip the checks for DELETE and
FLAGS_ONLY.  KVM doesn't allow moving the hva or changing the size, a gfn
change shows up as a MOVE even if flags are being modified, and the
checks are pointless for the DELETE case as userspace_addr and gfn_base
are zeroed by common KVM.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/s390/kvm/kvm-s390.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 81f90891db0f..c4d0ed5f3400 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -5020,7 +5020,14 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
 {
-	gpa_t size = new->npages * PAGE_SIZE;
+	gpa_t size;
+
+	/* When we are protected, we should not change the memory slots */
+	if (kvm_s390_pv_get_handle(kvm))
+		return -EINVAL;
+
+	if (change == KVM_MR_DELETE || change == KVM_MR_FLAGS_ONLY)
+		return 0;
 
 	/* A few sanity checks. We can have memory slots which have to be
 	   located/ended at a segment boundary (1MB). The memory in userland is
@@ -5030,15 +5037,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	if (new->userspace_addr & 0xffffful)
 		return -EINVAL;
 
+	size = new->npages * PAGE_SIZE;
 	if (size & 0xffffful)
 		return -EINVAL;
 
 	if ((new->base_gfn * PAGE_SIZE) + size > kvm->arch.mem_limit)
 		return -EINVAL;
 
-	/* When we are protected, we should not change the memory slots */
-	if (kvm_s390_pv_get_handle(kvm))
-		return -EINVAL;
 	return 0;
 }
 
-- 
2.33.1.1089.g2158813163f-goog

[PATCH v5.5 18/30] KVM: Don't make a full copy of the old memslot in __kvm_set_memory_region()

[Sean Christopherson]

Stop making a full copy of the old memslot in __kvm_set_memory_region()
now that metadata updates are handled by kvm_set_memslot(), i.e. now that
the old memslot's dirty bitmap doesn't need to be referenced after the
memslot and its pointer is modified/invalidated by kvm_set_memslot().

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 virt/kvm/kvm_main.c | 35 +++++++++++++----------------------
 1 file changed, 13 insertions(+), 22 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 6c7bbc452dae..bbaa01afac43 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1715,8 +1715,8 @@ static int kvm_set_memslot(struct kvm *kvm,
 int __kvm_set_memory_region(struct kvm *kvm,
 			    const struct kvm_userspace_memory_region *mem)
 {
-	struct kvm_memory_slot old, new;
-	struct kvm_memory_slot *tmp;
+	struct kvm_memory_slot *old, *tmp;
+	struct kvm_memory_slot new;
 	enum kvm_mr_change change;
 	int as_id, id;
 	int r;
@@ -1746,25 +1746,16 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		return -EINVAL;
 
 	/*
-	 * Make a full copy of the old memslot, the pointer will become stale
-	 * when the memslots are re-sorted by update_memslots(), and the old
-	 * memslot needs to be referenced after calling update_memslots(), e.g.
-	 * to free its resources and for arch specific behavior.
+	 * Note, the old memslot (and the pointer itself!) may be invalidated
+	 * and/or destroyed by kvm_set_memslot().
 	 */
-	tmp = id_to_memslot(__kvm_memslots(kvm, as_id), id);
-	if (tmp) {
-		old = *tmp;
-		tmp = NULL;
-	} else {
-		memset(&old, 0, sizeof(old));
-		old.id = id;
-	}
+	old = id_to_memslot(__kvm_memslots(kvm, as_id), id);
 
 	if (!mem->memory_size) {
-		if (!old.npages)
+		if (!old || !old->npages)
 			return -EINVAL;
 
-		if (WARN_ON_ONCE(kvm->nr_memslot_pages < old.npages))
+		if (WARN_ON_ONCE(kvm->nr_memslot_pages < old->npages))
 			return -EIO;
 
 		memset(&new, 0, sizeof(new));
@@ -1784,7 +1775,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	if (new.npages > KVM_MEM_MAX_NR_PAGES)
 		return -EINVAL;
 
-	if (!old.npages) {
+	if (!old || !old->npages) {
 		change = KVM_MR_CREATE;
 
 		/*
@@ -1794,14 +1785,14 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		if ((kvm->nr_memslot_pages + new.npages) < kvm->nr_memslot_pages)
 			return -EINVAL;
 	} else { /* Modify an existing slot. */
-		if ((new.userspace_addr != old.userspace_addr) ||
-		    (new.npages != old.npages) ||
-		    ((new.flags ^ old.flags) & KVM_MEM_READONLY))
+		if ((new.userspace_addr != old->userspace_addr) ||
+		    (new.npages != old->npages) ||
+		    ((new.flags ^ old->flags) & KVM_MEM_READONLY))
 			return -EINVAL;
 
-		if (new.base_gfn != old.base_gfn)
+		if (new.base_gfn != old->base_gfn)
 			change = KVM_MR_MOVE;
-		else if (new.flags != old.flags)
+		else if (new.flags != old->flags)
 			change = KVM_MR_FLAGS_ONLY;
 		else /* Nothing to change. */
 			return 0;
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 18/30] KVM: Don't make a full copy of the old memslot in __kvm_set_memory_region()

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> Stop making a full copy of the old memslot in __kvm_set_memory_region()
> now that metadata updates are handled by kvm_set_memslot(), i.e. now that
> the old memslot's dirty bitmap doesn't need to be referenced after the
> memslot and its pointer is modified/invalidated by kvm_set_memslot().
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

[PATCH v5.5 19/30] KVM: x86: Don't call kvm_mmu_change_mmu_pages() if the count hasn't changed

[Sean Christopherson]

There is no point in calling kvm_mmu_change_mmu_pages() for memslot
operations that don't change the total page count, so do it just for
KVM_MR_CREATE and KVM_MR_DELETE.

Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/x86.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 80183f7eadeb..4b0cb7390902 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11836,7 +11836,8 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
 {
-	if (!kvm->arch.n_requested_mmu_pages)
+	if (!kvm->arch.n_requested_mmu_pages &&
+	    (change == KVM_MR_CREATE || change == KVM_MR_DELETE))
 		kvm_mmu_change_mmu_pages(kvm,
 				kvm_mmu_calculate_default_mmu_pages(kvm));
 
-- 
2.33.1.1089.g2158813163f-goog

[PATCH v5.5 20/30] KVM: x86: Use nr_memslot_pages to avoid traversing the memslots array

[Sean Christopherson]

From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

There is no point in recalculating from scratch the total number of pages
in all memslots each time a memslot is created or deleted.  Use KVM's
cached nr_memslot_pages to compute the default max number of MMU pages.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
[sean: use common KVM field and rework changelog accordingly]
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/include/asm/kvm_host.h |  1 -
 arch/x86/kvm/mmu/mmu.c          | 24 ------------------------
 arch/x86/kvm/x86.c              | 11 ++++++++---
 3 files changed, 8 insertions(+), 28 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 88fce6ab4bbd..3fe155ece015 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1582,7 +1582,6 @@ void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm,
 				   const struct kvm_memory_slot *memslot);
 void kvm_mmu_zap_all(struct kvm *kvm);
 void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm, u64 gen);
-unsigned long kvm_mmu_calculate_default_mmu_pages(struct kvm *kvm);
 void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned long kvm_nr_mmu_pages);
 
 int load_pdptrs(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, unsigned long cr3);
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 354d2ca92df4..564781585fd2 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -6141,30 +6141,6 @@ int kvm_mmu_module_init(void)
 	return ret;
 }
 
-/*
- * Calculate mmu pages needed for kvm.
- */
-unsigned long kvm_mmu_calculate_default_mmu_pages(struct kvm *kvm)
-{
-	unsigned long nr_mmu_pages;
-	unsigned long nr_pages = 0;
-	struct kvm_memslots *slots;
-	struct kvm_memory_slot *memslot;
-	int i;
-
-	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
-		slots = __kvm_memslots(kvm, i);
-
-		kvm_for_each_memslot(memslot, slots)
-			nr_pages += memslot->npages;
-	}
-
-	nr_mmu_pages = nr_pages * KVM_PERMILLE_MMU_PAGES / 1000;
-	nr_mmu_pages = max(nr_mmu_pages, KVM_MIN_ALLOC_MMU_PAGES);
-
-	return nr_mmu_pages;
-}
-
 void kvm_mmu_destroy(struct kvm_vcpu *vcpu)
 {
 	kvm_mmu_unload(vcpu);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4b0cb7390902..9a0440e22ede 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11837,9 +11837,14 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 				enum kvm_mr_change change)
 {
 	if (!kvm->arch.n_requested_mmu_pages &&
-	    (change == KVM_MR_CREATE || change == KVM_MR_DELETE))
-		kvm_mmu_change_mmu_pages(kvm,
-				kvm_mmu_calculate_default_mmu_pages(kvm));
+	    (change == KVM_MR_CREATE || change == KVM_MR_DELETE)) {
+		unsigned long nr_mmu_pages;
+
+		nr_mmu_pages = kvm->nr_memslot_pages * KVM_PERMILLE_MMU_PAGES;
+		nr_mmu_pages /= 1000;
+		nr_mmu_pages = max(nr_mmu_pages, KVM_MIN_ALLOC_MMU_PAGES);
+		kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
+	}
 
 	kvm_mmu_slot_apply_flags(kvm, old, new, change);
 
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 20/30] KVM: x86: Use nr_memslot_pages to avoid traversing the memslots array

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> 
> There is no point in recalculating from scratch the total number of pages
> in all memslots each time a memslot is created or deleted.  Use KVM's
> cached nr_memslot_pages to compute the default max number of MMU pages.
> 
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> [sean: use common KVM field and rework changelog accordingly]
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   arch/x86/include/asm/kvm_host.h |  1 -
>   arch/x86/kvm/mmu/mmu.c          | 24 ------------------------
>   arch/x86/kvm/x86.c              | 11 ++++++++---
>   3 files changed, 8 insertions(+), 28 deletions(-)
> 
(..)
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -11837,9 +11837,14 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
>   				enum kvm_mr_change change)
>   {
>   	if (!kvm->arch.n_requested_mmu_pages &&
> -	    (change == KVM_MR_CREATE || change == KVM_MR_DELETE))
> -		kvm_mmu_change_mmu_pages(kvm,
> -				kvm_mmu_calculate_default_mmu_pages(kvm));
> +	    (change == KVM_MR_CREATE || change == KVM_MR_DELETE)) {
> +		unsigned long nr_mmu_pages;
> +
> +		nr_mmu_pages = kvm->nr_memslot_pages * KVM_PERMILLE_MMU_PAGES;

Unfortunately, even if kvm->nr_memslot_pages is capped at ULONG_MAX then
this value multiplied by 20 can still overflow an unsigned long variable.

Thanks,
Maciej

Re: [PATCH v5.5 20/30] KVM: x86: Use nr_memslot_pages to avoid traversing the memslots array

[Sean Christopherson]

On Tue, Nov 09, 2021, Maciej S. Szmigiero wrote:
> On 04.11.2021 01:25, Sean Christopherson wrote:
> > From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> > 
> > There is no point in recalculating from scratch the total number of pages
> > in all memslots each time a memslot is created or deleted.  Use KVM's
> > cached nr_memslot_pages to compute the default max number of MMU pages.
> > 
> > Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> > [sean: use common KVM field and rework changelog accordingly]

Heh, and I forgot to add "and introduce bugs"

> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > ---
> >   arch/x86/include/asm/kvm_host.h |  1 -
> >   arch/x86/kvm/mmu/mmu.c          | 24 ------------------------
> >   arch/x86/kvm/x86.c              | 11 ++++++++---
> >   3 files changed, 8 insertions(+), 28 deletions(-)
> > 
> (..)
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -11837,9 +11837,14 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
> >   				enum kvm_mr_change change)
> >   {
> >   	if (!kvm->arch.n_requested_mmu_pages &&
> > -	    (change == KVM_MR_CREATE || change == KVM_MR_DELETE))
> > -		kvm_mmu_change_mmu_pages(kvm,
> > -				kvm_mmu_calculate_default_mmu_pages(kvm));
> > +	    (change == KVM_MR_CREATE || change == KVM_MR_DELETE)) {
> > +		unsigned long nr_mmu_pages;
> > +
> > +		nr_mmu_pages = kvm->nr_memslot_pages * KVM_PERMILLE_MMU_PAGES;
> 
> Unfortunately, even if kvm->nr_memslot_pages is capped at ULONG_MAX then
> this value multiplied by 20 can still overflow an unsigned long variable.

Doh.  And that likely subtly avoided by the compiler collapsing the "* 20 / 1000"
into "/ 50".

Any objection to adding a patch to cut out the multiplication entirely?  Well, cut
it from the source code, looks like gcc generates some fancy SHR+MUL to do the
divide.

I'm thinking this:

#define KVM_MEMSLOT_PAGES_TO_MMU_PAGES_RATIO 50


	...

	nr_mmu_pages = nr_pages / KVM_MEMSLOT_PAGES_TO_MMU_PAGES_RATIO;

Re: [PATCH v5.5 20/30] KVM: x86: Use nr_memslot_pages to avoid traversing the memslots array

[Maciej S. Szmigiero]

On 09.11.2021 02:34, Sean Christopherson wrote:
> On Tue, Nov 09, 2021, Maciej S. Szmigiero wrote:
>> On 04.11.2021 01:25, Sean Christopherson wrote:
>>> From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
>>>
>>> There is no point in recalculating from scratch the total number of pages
>>> in all memslots each time a memslot is created or deleted.  Use KVM's
>>> cached nr_memslot_pages to compute the default max number of MMU pages.
>>>
>>> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
>>> [sean: use common KVM field and rework changelog accordingly]
> 
> Heh, and I forgot to add "and introduce bugs"
> 
>>> Signed-off-by: Sean Christopherson <seanjc@google.com>
>>> ---
>>>    arch/x86/include/asm/kvm_host.h |  1 -
>>>    arch/x86/kvm/mmu/mmu.c          | 24 ------------------------
>>>    arch/x86/kvm/x86.c              | 11 ++++++++---
>>>    3 files changed, 8 insertions(+), 28 deletions(-)
>>>
>> (..)
>>> --- a/arch/x86/kvm/x86.c
>>> +++ b/arch/x86/kvm/x86.c
>>> @@ -11837,9 +11837,14 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
>>>    				enum kvm_mr_change change)
>>>    {
>>>    	if (!kvm->arch.n_requested_mmu_pages &&
>>> -	    (change == KVM_MR_CREATE || change == KVM_MR_DELETE))
>>> -		kvm_mmu_change_mmu_pages(kvm,
>>> -				kvm_mmu_calculate_default_mmu_pages(kvm));
>>> +	    (change == KVM_MR_CREATE || change == KVM_MR_DELETE)) {
>>> +		unsigned long nr_mmu_pages;
>>> +
>>> +		nr_mmu_pages = kvm->nr_memslot_pages * KVM_PERMILLE_MMU_PAGES;
>>
>> Unfortunately, even if kvm->nr_memslot_pages is capped at ULONG_MAX then
>> this value multiplied by 20 can still overflow an unsigned long variable.
> 
> Doh.  And that likely subtly avoided by the compiler collapsing the "* 20 / 1000"
> into "/ 50".

Unfortunately in this case (but fortunately in general) C has well-defined
unsigned overflow behavior so if this code has an overflow by its naive
reading the compiler is not allowed to transform it to a form which
doesn't have this overflow (as it will result in a different value).

> Any objection to adding a patch to cut out the multiplication entirely?  Well, cut
> it from the source code, looks like gcc generates some fancy SHR+MUL to do the
> divide.
> 
> I'm thinking this:
> 
> #define KVM_MEMSLOT_PAGES_TO_MMU_PAGES_RATIO 50
> 
> 
> 	...
> 
> 	nr_mmu_pages = nr_pages / KVM_MEMSLOT_PAGES_TO_MMU_PAGES_RATIO;
> 
> 

I agree this would be a good solution to our problem, since this macro is
unlikely to be converted into something user-configurable in the future.
So its units don't matter.

Thanks,
Maciej

[PATCH v5.5 21/30] KVM: Integrate gfn_to_memslot_approx() into search_memslots()

[Sean Christopherson]

From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

s390 arch has gfn_to_memslot_approx() which is almost identical to
search_memslots(), differing only in that in case the gfn falls in a hole
one of the memslots bordering the hole is returned.

Add this lookup mode as an option to search_memslots() so we don't have two
almost identical functions for looking up a memslot by its gfn.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
[sean: tweaked helper names to keep gfn_to_memslot_approx() in s390]
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/s390/kvm/kvm-s390.c | 45 +++++++---------------------------------
 include/linux/kvm_host.h | 35 ++++++++++++++++++++++++-------
 virt/kvm/kvm_main.c      |  2 +-
 3 files changed, 36 insertions(+), 46 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index c4d0ed5f3400..4e032e176216 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1941,41 +1941,6 @@ static long kvm_s390_set_skeys(struct kvm *kvm, struct kvm_s390_skeys *args)
 /* for consistency */
 #define KVM_S390_CMMA_SIZE_MAX ((u32)KVM_S390_SKEYS_MAX)
 
-/*
- * Similar to gfn_to_memslot, but returns the index of a memslot also when the
- * address falls in a hole. In that case the index of one of the memslots
- * bordering the hole is returned.
- */
-static int gfn_to_memslot_approx(struct kvm_memslots *slots, gfn_t gfn)
-{
-	int start = 0, end = slots->used_slots;
-	int slot = atomic_read(&slots->last_used_slot);
-	struct kvm_memory_slot *memslots = slots->memslots;
-
-	if (gfn >= memslots[slot].base_gfn &&
-	    gfn < memslots[slot].base_gfn + memslots[slot].npages)
-		return slot;
-
-	while (start < end) {
-		slot = start + (end - start) / 2;
-
-		if (gfn >= memslots[slot].base_gfn)
-			end = slot;
-		else
-			start = slot + 1;
-	}
-
-	if (start >= slots->used_slots)
-		return slots->used_slots - 1;
-
-	if (gfn >= memslots[start].base_gfn &&
-	    gfn < memslots[start].base_gfn + memslots[start].npages) {
-		atomic_set(&slots->last_used_slot, start);
-	}
-
-	return start;
-}
-
 static int kvm_s390_peek_cmma(struct kvm *kvm, struct kvm_s390_cmma_log *args,
 			      u8 *res, unsigned long bufsize)
 {
@@ -1999,11 +1964,17 @@ static int kvm_s390_peek_cmma(struct kvm *kvm, struct kvm_s390_cmma_log *args,
 	return 0;
 }
 
+static struct kvm_memory_slot *gfn_to_memslot_approx(struct kvm_memslots *slots,
+						     gfn_t gfn)
+{
+	return ____gfn_to_memslot(slots, gfn, true);
+}
+
 static unsigned long kvm_s390_next_dirty_cmma(struct kvm_memslots *slots,
 					      unsigned long cur_gfn)
 {
-	int slotidx = gfn_to_memslot_approx(slots, cur_gfn);
-	struct kvm_memory_slot *ms = slots->memslots + slotidx;
+	struct kvm_memory_slot *ms = gfn_to_memslot_approx(slots, cur_gfn);
+	int slotidx = ms - slots->memslots;
 	unsigned long ofs = cur_gfn - ms->base_gfn;
 
 	if (ms->base_gfn + ms->npages <= cur_gfn) {
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 2ef946e94a73..9d46937a3a4e 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1230,10 +1230,14 @@ try_get_memslot(struct kvm_memslots *slots, int slot_index, gfn_t gfn)
  * Returns a pointer to the memslot that contains gfn and records the index of
  * the slot in index. Otherwise returns NULL.
  *
+ * With "approx" set returns the memslot also when the address falls
+ * in a hole. In that case one of the memslots bordering the hole is
+ * returned.
+ *
  * IMPORTANT: Slots are sorted from highest GFN to lowest GFN!
  */
 static inline struct kvm_memory_slot *
-search_memslots(struct kvm_memslots *slots, gfn_t gfn, int *index)
+search_memslots(struct kvm_memslots *slots, gfn_t gfn, int *index, bool approx)
 {
 	int start = 0, end = slots->used_slots;
 	struct kvm_memory_slot *memslots = slots->memslots;
@@ -1251,22 +1255,26 @@ search_memslots(struct kvm_memslots *slots, gfn_t gfn, int *index)
 			start = slot + 1;
 	}
 
+	if (approx && start >= slots->used_slots) {
+		*index = slots->used_slots - 1;
+		return &memslots[slots->used_slots - 1];
+	}
+
 	slot = try_get_memslot(slots, start, gfn);
 	if (slot) {
 		*index = start;
 		return slot;
 	}
+	if (approx) {
+		*index = start;
+		return &memslots[start];
+	}
 
 	return NULL;
 }
 
-/*
- * __gfn_to_memslot() and its descendants are here because it is called from
- * non-modular code in arch/powerpc/kvm/book3s_64_vio{,_hv}.c. gfn_to_memslot()
- * itself isn't here as an inline because that would bloat other code too much.
- */
 static inline struct kvm_memory_slot *
-__gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn)
+____gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn, bool approx)
 {
 	struct kvm_memory_slot *slot;
 	int slot_index = atomic_read(&slots->last_used_slot);
@@ -1275,7 +1283,7 @@ __gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn)
 	if (slot)
 		return slot;
 
-	slot = search_memslots(slots, gfn, &slot_index);
+	slot = search_memslots(slots, gfn, &slot_index, approx);
 	if (slot) {
 		atomic_set(&slots->last_used_slot, slot_index);
 		return slot;
@@ -1284,6 +1292,17 @@ __gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn)
 	return NULL;
 }
 
+/*
+ * __gfn_to_memslot() and its descendants are here to allow arch code to inline
+ * the lookups in hot paths.  gfn_to_memslot() itself isn't here as an inline
+ * because that would bloat other code too much.
+ */
+static inline struct kvm_memory_slot *
+__gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn)
+{
+	return ____gfn_to_memslot(slots, gfn, false);
+}
+
 static inline unsigned long
 __gfn_to_hva_memslot(const struct kvm_memory_slot *slot, gfn_t gfn)
 {
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index bbaa01afac43..a2d51ce957e1 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2126,7 +2126,7 @@ struct kvm_memory_slot *kvm_vcpu_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn
 	 * search_memslots() instead of __gfn_to_memslot() to avoid
 	 * thrashing the VM-wide last_used_index in kvm_memslots.
 	 */
-	slot = search_memslots(slots, gfn, &slot_index);
+	slot = search_memslots(slots, gfn, &slot_index, false);
 	if (slot) {
 		vcpu->last_used_slot = slot_index;
 		return slot;
-- 
2.33.1.1089.g2158813163f-goog

[PATCH v5.5 22/30] KVM: Move WARN on invalid memslot index to update_memslots()

[Sean Christopherson]

From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

Since kvm_memslot_move_forward() can theoretically return a negative
memslot index even when kvm_memslot_move_backward() returned a positive one
(and so did not WARN) let's just move the warning to the common code.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 virt/kvm/kvm_main.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a2d51ce957e1..d45d574a5a2d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1307,8 +1307,7 @@ static inline int kvm_memslot_move_backward(struct kvm_memslots *slots,
 	struct kvm_memory_slot *mslots = slots->memslots;
 	int i;
 
-	if (WARN_ON_ONCE(slots->id_to_index[memslot->id] == -1) ||
-	    WARN_ON_ONCE(!slots->used_slots))
+	if (slots->id_to_index[memslot->id] == -1 || !slots->used_slots)
 		return -1;
 
 	/*
@@ -1412,6 +1411,9 @@ static void update_memslots(struct kvm_memslots *slots,
 			i = kvm_memslot_move_backward(slots, memslot);
 		i = kvm_memslot_move_forward(slots, memslot, i);
 
+		if (WARN_ON_ONCE(i < 0))
+			return;
+
 		/*
 		 * Copy the memslot to its new position in memslots and update
 		 * its index accordingly.
-- 
2.33.1.1089.g2158813163f-goog

[PATCH v5.5 23/30] KVM: Resolve memslot ID via a hash table instead of via a static array

[Sean Christopherson]

From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

Memslot ID to the corresponding memslot mappings are currently kept as
indices in static id_to_index array.
The size of this array depends on the maximum allowed memslot count
(regardless of the number of memslots actually in use).

This has become especially problematic recently, when memslot count cap was
removed, so the maximum count is now full 32k memslots - the maximum
allowed by the current KVM API.

Keeping these IDs in a hash table (instead of an array) avoids this
problem.

Resolving a memslot ID to the actual memslot (instead of its index) will
also enable transitioning away from an array-based implementation of the
whole memslots structure in a later commit.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 include/linux/kvm_host.h | 16 +++----
 virt/kvm/kvm_main.c      | 96 +++++++++++++++++++++++++++++++---------
 2 files changed, 84 insertions(+), 28 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 9d46937a3a4e..81003e3acd53 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -29,6 +29,7 @@
 #include <linux/refcount.h>
 #include <linux/nospec.h>
 #include <linux/notifier.h>
+#include <linux/hashtable.h>
 #include <asm/signal.h>
 
 #include <linux/kvm.h>
@@ -425,6 +426,7 @@ static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)
 #define KVM_MEM_MAX_NR_PAGES ((1UL << 31) - 1)
 
 struct kvm_memory_slot {
+	struct hlist_node id_node;
 	gfn_t base_gfn;
 	unsigned long npages;
 	unsigned long *dirty_bitmap;
@@ -527,7 +529,7 @@ static inline int kvm_arch_vcpu_memslots_id(struct kvm_vcpu *vcpu)
 struct kvm_memslots {
 	u64 generation;
 	/* The mapping table from slot id to the index in memslots[]. */
-	short id_to_index[KVM_MEM_SLOTS_NUM];
+	DECLARE_HASHTABLE(id_hash, 7);
 	atomic_t last_used_slot;
 	int used_slots;
 	struct kvm_memory_slot memslots[];
@@ -789,16 +791,14 @@ static inline struct kvm_memslots *kvm_vcpu_memslots(struct kvm_vcpu *vcpu)
 static inline
 struct kvm_memory_slot *id_to_memslot(struct kvm_memslots *slots, int id)
 {
-	int index = slots->id_to_index[id];
 	struct kvm_memory_slot *slot;
 
-	if (index < 0)
-		return NULL;
+	hash_for_each_possible(slots->id_hash, slot, id_node, id) {
+		if (slot->id == id)
+			return slot;
+	}
 
-	slot = &slots->memslots[index];
-
-	WARN_ON(slot->id != id);
-	return slot;
+	return NULL;
 }
 
 /*
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d45d574a5a2d..13c497abaab8 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -853,15 +853,13 @@ static void kvm_destroy_pm_notifier(struct kvm *kvm)
 
 static struct kvm_memslots *kvm_alloc_memslots(void)
 {
-	int i;
 	struct kvm_memslots *slots;
 
 	slots = kvzalloc(sizeof(struct kvm_memslots), GFP_KERNEL_ACCOUNT);
 	if (!slots)
 		return NULL;
 
-	for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
-		slots->id_to_index[i] = -1;
+	hash_init(slots->id_hash);
 
 	return slots;
 }
@@ -1259,17 +1257,49 @@ static int kvm_alloc_dirty_bitmap(struct kvm_memory_slot *memslot)
 	return 0;
 }
 
+static void kvm_replace_memslot(struct kvm_memslots *slots,
+				struct kvm_memory_slot *old,
+				struct kvm_memory_slot *new)
+{
+	/*
+	 * Remove the old memslot from the hash list, copying the node data
+	 * would corrupt the list.
+	 */
+	if (old) {
+		hash_del(&old->id_node);
+
+		if (!new)
+			return;
+	}
+
+	/* Copy the source *data*, not the pointer, to the destination. */
+	if (old)
+		*new = *old;
+
+	/* (Re)Add the new memslot. */
+	hash_add(slots->id_hash, &new->id_node, new->id);
+}
+
+static void kvm_shift_memslot(struct kvm_memslots *slots, int dst, int src)
+{
+	struct kvm_memory_slot *mslots = slots->memslots;
+
+	kvm_replace_memslot(slots, &mslots[src], &mslots[dst]);
+}
+
 /*
  * Delete a memslot by decrementing the number of used slots and shifting all
  * other entries in the array forward one spot.
+ * @memslot is a detached dummy struct with just .id and .as_id filled.
  */
 static inline void kvm_memslot_delete(struct kvm_memslots *slots,
 				      struct kvm_memory_slot *memslot)
 {
 	struct kvm_memory_slot *mslots = slots->memslots;
+	struct kvm_memory_slot *oldslot = id_to_memslot(slots, memslot->id);
 	int i;
 
-	if (WARN_ON(slots->id_to_index[memslot->id] == -1))
+	if (WARN_ON(!oldslot))
 		return;
 
 	slots->used_slots--;
@@ -1277,12 +1307,17 @@ static inline void kvm_memslot_delete(struct kvm_memslots *slots,
 	if (atomic_read(&slots->last_used_slot) >= slots->used_slots)
 		atomic_set(&slots->last_used_slot, 0);
 
-	for (i = slots->id_to_index[memslot->id]; i < slots->used_slots; i++) {
-		mslots[i] = mslots[i + 1];
-		slots->id_to_index[mslots[i].id] = i;
-	}
+	/*
+	 * Remove the to-be-deleted memslot from the list _before_ shifting
+	 * the trailing memslots forward, its data will be overwritten.
+	 * Defer the (somewhat pointless) copying of the memslot until after
+	 * the last slot has been shifted to avoid overwriting said last slot.
+	 */
+	kvm_replace_memslot(slots, oldslot, NULL);
+
+	for (i = oldslot - mslots; i < slots->used_slots; i++)
+		kvm_shift_memslot(slots, i, i + 1);
 	mslots[i] = *memslot;
-	slots->id_to_index[memslot->id] = -1;
 }
 
 /*
@@ -1300,30 +1335,39 @@ static inline int kvm_memslot_insert_back(struct kvm_memslots *slots)
  * itself is not preserved in the array, i.e. not swapped at this time, only
  * its new index into the array is tracked.  Returns the changed memslot's
  * current index into the memslots array.
+ * The memslot at the returned index will not be in @slots->id_hash by then.
+ * @memslot is a detached struct with desired final data of the changed slot.
  */
 static inline int kvm_memslot_move_backward(struct kvm_memslots *slots,
 					    struct kvm_memory_slot *memslot)
 {
 	struct kvm_memory_slot *mslots = slots->memslots;
+	struct kvm_memory_slot *oldslot = id_to_memslot(slots, memslot->id);
 	int i;
 
-	if (slots->id_to_index[memslot->id] == -1 || !slots->used_slots)
+	if (!oldslot || !slots->used_slots)
 		return -1;
 
+	/*
+	 * Delete the slot from the hash table before sorting the remaining
+	 * slots, the slot's data may be overwritten when copying slots as part
+	 * of the sorting proccess.  update_memslots() will unconditionally
+	 * rewrite the entire slot and re-add it to the hash table.
+	 */
+	kvm_replace_memslot(slots, oldslot, NULL);
+
 	/*
 	 * Move the target memslot backward in the array by shifting existing
 	 * memslots with a higher GFN (than the target memslot) towards the
 	 * front of the array.
 	 */
-	for (i = slots->id_to_index[memslot->id]; i < slots->used_slots - 1; i++) {
+	for (i = oldslot - mslots; i < slots->used_slots - 1; i++) {
 		if (memslot->base_gfn > mslots[i + 1].base_gfn)
 			break;
 
 		WARN_ON_ONCE(memslot->base_gfn == mslots[i + 1].base_gfn);
 
-		/* Shift the next memslot forward one and update its index. */
-		mslots[i] = mslots[i + 1];
-		slots->id_to_index[mslots[i].id] = i;
+		kvm_shift_memslot(slots, i, i + 1);
 	}
 	return i;
 }
@@ -1334,6 +1378,10 @@ static inline int kvm_memslot_move_backward(struct kvm_memslots *slots,
  * is not preserved in the array, i.e. not swapped at this time, only its new
  * index into the array is tracked.  Returns the changed memslot's final index
  * into the memslots array.
+ * The memslot at the returned index will not be in @slots->id_hash by then.
+ * @memslot is a detached struct with desired final data of the new or
+ * changed slot.
+ * Assumes that the memslot at @start index is not in @slots->id_hash.
  */
 static inline int kvm_memslot_move_forward(struct kvm_memslots *slots,
 					   struct kvm_memory_slot *memslot,
@@ -1348,9 +1396,7 @@ static inline int kvm_memslot_move_forward(struct kvm_memslots *slots,
 
 		WARN_ON_ONCE(memslot->base_gfn == mslots[i - 1].base_gfn);
 
-		/* Shift the next memslot back one and update its index. */
-		mslots[i] = mslots[i - 1];
-		slots->id_to_index[mslots[i].id] = i;
+		kvm_shift_memslot(slots, i, i - 1);
 	}
 	return i;
 }
@@ -1395,6 +1441,9 @@ static inline int kvm_memslot_move_forward(struct kvm_memslots *slots,
  * most likely to be referenced, sorting it to the front of the array was
  * advantageous.  The current binary search starts from the middle of the array
  * and uses an LRU pointer to improve performance for all memslots and GFNs.
+ *
+ * @memslot is a detached struct, not a part of the current or new memslot
+ * array.
  */
 static void update_memslots(struct kvm_memslots *slots,
 			    struct kvm_memory_slot *memslot,
@@ -1419,7 +1468,7 @@ static void update_memslots(struct kvm_memslots *slots,
 		 * its index accordingly.
 		 */
 		slots->memslots[i] = *memslot;
-		slots->id_to_index[memslot->id] = i;
+		kvm_replace_memslot(slots, NULL, &slots->memslots[i]);
 	}
 }
 
@@ -1512,6 +1561,7 @@ static struct kvm_memslots *kvm_dup_memslots(struct kvm_memslots *old,
 {
 	struct kvm_memslots *slots;
 	size_t new_size;
+	struct kvm_memory_slot *memslot;
 
 	if (change == KVM_MR_CREATE)
 		new_size = kvm_memslots_size(old->used_slots + 1);
@@ -1519,8 +1569,14 @@ static struct kvm_memslots *kvm_dup_memslots(struct kvm_memslots *old,
 		new_size = kvm_memslots_size(old->used_slots);
 
 	slots = kvzalloc(new_size, GFP_KERNEL_ACCOUNT);
-	if (likely(slots))
-		memcpy(slots, old, kvm_memslots_size(old->used_slots));
+	if (unlikely(!slots))
+		return NULL;
+
+	memcpy(slots, old, kvm_memslots_size(old->used_slots));
+
+	hash_init(slots->id_hash);
+	kvm_for_each_memslot(memslot, slots)
+		hash_add(slots->id_hash, &memslot->id_node, memslot->id);
 
 	return slots;
 }
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 23/30] KVM: Resolve memslot ID via a hash table instead of via a static array

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> 
> Memslot ID to the corresponding memslot mappings are currently kept as
> indices in static id_to_index array.
> The size of this array depends on the maximum allowed memslot count
> (regardless of the number of memslots actually in use).
> 
> This has become especially problematic recently, when memslot count cap was
> removed, so the maximum count is now full 32k memslots - the maximum
> allowed by the current KVM API.
> 
> Keeping these IDs in a hash table (instead of an array) avoids this
> problem.
> 
> Resolving a memslot ID to the actual memslot (instead of its index) will
> also enable transitioning away from an array-based implementation of the
> whole memslots structure in a later commit.
> 
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> Co-developed-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   include/linux/kvm_host.h | 16 +++----
>   virt/kvm/kvm_main.c      | 96 +++++++++++++++++++++++++++++++---------
>   2 files changed, 84 insertions(+), 28 deletions(-)
> 
(..)
> @@ -1259,17 +1257,49 @@ static int kvm_alloc_dirty_bitmap(struct kvm_memory_slot *memslot)
>   	return 0;
>   }
>   
> +static void kvm_replace_memslot(struct kvm_memslots *slots,
> +				struct kvm_memory_slot *old,
> +				struct kvm_memory_slot *new)
> +{
> +	/*
> +	 * Remove the old memslot from the hash list, copying the node data
> +	 * would corrupt the list.
> +	 */
> +	if (old) {
> +		hash_del(&old->id_node);
> +
> +		if (!new)
> +			return;
> +	}
> +
> +	/* Copy the source *data*, not the pointer, to the destination. */
> +	if (old)
> +		*new = *old;

This way of writing it (that, is re-checking whether "old" is not-NULL)
suggests that it could have been set to NULL inside the previous block
(since the last check), which isn't true.

Thanks,
Maciej

Re: [PATCH v5.5 23/30] KVM: Resolve memslot ID via a hash table instead of via a static array

[Sean Christopherson]

On Fri, Nov 12, 2021, Maciej S. Szmigiero wrote:
> On 04.11.2021 01:25, Sean Christopherson wrote:
> > From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> > 
> > Memslot ID to the corresponding memslot mappings are currently kept as
> > indices in static id_to_index array.
> > The size of this array depends on the maximum allowed memslot count
> > (regardless of the number of memslots actually in use).
> > 
> > This has become especially problematic recently, when memslot count cap was
> > removed, so the maximum count is now full 32k memslots - the maximum
> > allowed by the current KVM API.
> > 
> > Keeping these IDs in a hash table (instead of an array) avoids this
> > problem.
> > 
> > Resolving a memslot ID to the actual memslot (instead of its index) will
> > also enable transitioning away from an array-based implementation of the
> > whole memslots structure in a later commit.
> > 
> > Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> > Co-developed-by: Sean Christopherson <seanjc@google.com>
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > ---
> >   include/linux/kvm_host.h | 16 +++----
> >   virt/kvm/kvm_main.c      | 96 +++++++++++++++++++++++++++++++---------
> >   2 files changed, 84 insertions(+), 28 deletions(-)
> > 
> (..)
> > @@ -1259,17 +1257,49 @@ static int kvm_alloc_dirty_bitmap(struct kvm_memory_slot *memslot)
> >   	return 0;
> >   }
> > +static void kvm_replace_memslot(struct kvm_memslots *slots,
> > +				struct kvm_memory_slot *old,
> > +				struct kvm_memory_slot *new)
> > +{
> > +	/*
> > +	 * Remove the old memslot from the hash list, copying the node data
> > +	 * would corrupt the list.
> > +	 */
> > +	if (old) {
> > +		hash_del(&old->id_node);
> > +
> > +		if (!new)
> > +			return;
> > +	}
> > +
> > +	/* Copy the source *data*, not the pointer, to the destination. */
> > +	if (old)
> > +		*new = *old;
> 
> This way of writing it (that, is re-checking whether "old" is not-NULL)
> suggests that it could have been set to NULL inside the previous block
> (since the last check), which isn't true.

Yeah, I think I was trying to minimize the logic delta in future patches, but
looking back at the diffs, that didn't pan out.  I've no objection to folding
the two together.

[PATCH v5.5 24/30] KVM: Use interval tree to do fast hva lookup in memslots

[Sean Christopherson]

From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

The current memslots implementation only allows quick binary search by gfn,
quick lookup by hva is not possible - the implementation has to do a linear
scan of the whole memslots array, even though the operation being performed
might apply just to a single memslot.

This significantly hurts performance of per-hva operations with higher
memslot counts.

Since hva ranges can overlap between memslots an interval tree is needed
for tracking them.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
[sean: handle interval tree updates in kvm_replace_memslot()]
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/arm64/kvm/Kconfig   |  1 +
 arch/mips/kvm/Kconfig    |  1 +
 arch/powerpc/kvm/Kconfig |  1 +
 arch/s390/kvm/Kconfig    |  1 +
 arch/x86/kvm/Kconfig     |  1 +
 include/linux/kvm_host.h |  3 ++
 virt/kvm/kvm_main.c      | 60 +++++++++++++++++++++++++++++-----------
 7 files changed, 52 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index d7eec0b43744..42185dcc9596 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -38,6 +38,7 @@ menuconfig KVM
 	select HAVE_KVM_IRQ_BYPASS
 	select HAVE_KVM_VCPU_RUN_PID_CHANGE
 	select SCHED_INFO
+	select INTERVAL_TREE
 	help
 	  Support hosting virtualized guest machines.
 
diff --git a/arch/mips/kvm/Kconfig b/arch/mips/kvm/Kconfig
index a77297480f56..91d197bee9c0 100644
--- a/arch/mips/kvm/Kconfig
+++ b/arch/mips/kvm/Kconfig
@@ -27,6 +27,7 @@ config KVM
 	select KVM_MMIO
 	select MMU_NOTIFIER
 	select SRCU
+	select INTERVAL_TREE
 	help
 	  Support for hosting Guest kernels.
 
diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
index ff581d70f20c..e4c24f524ba8 100644
--- a/arch/powerpc/kvm/Kconfig
+++ b/arch/powerpc/kvm/Kconfig
@@ -26,6 +26,7 @@ config KVM
 	select KVM_VFIO
 	select IRQ_BYPASS_MANAGER
 	select HAVE_KVM_IRQ_BYPASS
+	select INTERVAL_TREE
 
 config KVM_BOOK3S_HANDLER
 	bool
diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig
index 67a8e770e369..2e84d3922f7c 100644
--- a/arch/s390/kvm/Kconfig
+++ b/arch/s390/kvm/Kconfig
@@ -33,6 +33,7 @@ config KVM
 	select HAVE_KVM_NO_POLL
 	select SRCU
 	select KVM_VFIO
+	select INTERVAL_TREE
 	help
 	  Support hosting paravirtualized guest machines using the SIE
 	  virtualization capability on the mainframe. This should work
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 619186138176..7618bef0a4a9 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -43,6 +43,7 @@ config KVM
 	select KVM_GENERIC_DIRTYLOG_READ_PROTECT
 	select KVM_VFIO
 	select SRCU
+	select INTERVAL_TREE
 	select HAVE_KVM_PM_NOTIFIER if PM
 	help
 	  Support hosting fully virtualized guest machines using hardware
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 81003e3acd53..d0363e2ba098 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -30,6 +30,7 @@
 #include <linux/nospec.h>
 #include <linux/notifier.h>
 #include <linux/hashtable.h>
+#include <linux/interval_tree.h>
 #include <asm/signal.h>
 
 #include <linux/kvm.h>
@@ -427,6 +428,7 @@ static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)
 
 struct kvm_memory_slot {
 	struct hlist_node id_node;
+	struct interval_tree_node hva_node;
 	gfn_t base_gfn;
 	unsigned long npages;
 	unsigned long *dirty_bitmap;
@@ -528,6 +530,7 @@ static inline int kvm_arch_vcpu_memslots_id(struct kvm_vcpu *vcpu)
  */
 struct kvm_memslots {
 	u64 generation;
+	struct rb_root_cached hva_tree;
 	/* The mapping table from slot id to the index in memslots[]. */
 	DECLARE_HASHTABLE(id_hash, 7);
 	atomic_t last_used_slot;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 13c497abaab8..f2235c430e64 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -498,6 +498,12 @@ static void kvm_null_fn(void)
 }
 #define IS_KVM_NULL_FN(fn) ((fn) == (void *)kvm_null_fn)
 
+/* Iterate over each memslot intersecting [start, last] (inclusive) range */
+#define kvm_for_each_memslot_in_hva_range(node, slots, start, last)	     \
+	for (node = interval_tree_iter_first(&slots->hva_tree, start, last); \
+	     node;							     \
+	     node = interval_tree_iter_next(node, start, last))	     \
+
 static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
 						  const struct kvm_hva_range *range)
 {
@@ -507,6 +513,9 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
 	struct kvm_memslots *slots;
 	int i, idx;
 
+	if (WARN_ON_ONCE(range->end <= range->start))
+		return 0;
+
 	/* A null handler is allowed if and only if on_lock() is provided. */
 	if (WARN_ON_ONCE(IS_KVM_NULL_FN(range->on_lock) &&
 			 IS_KVM_NULL_FN(range->handler)))
@@ -515,15 +524,17 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
 	idx = srcu_read_lock(&kvm->srcu);
 
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
+		struct interval_tree_node *node;
+
 		slots = __kvm_memslots(kvm, i);
-		kvm_for_each_memslot(slot, slots) {
+		kvm_for_each_memslot_in_hva_range(node, slots,
+						  range->start, range->end - 1) {
 			unsigned long hva_start, hva_end;
 
+			slot = container_of(node, struct kvm_memory_slot, hva_node);
 			hva_start = max(range->start, slot->userspace_addr);
 			hva_end = min(range->end, slot->userspace_addr +
 						  (slot->npages << PAGE_SHIFT));
-			if (hva_start >= hva_end)
-				continue;
 
 			/*
 			 * To optimize for the likely case where the address
@@ -859,6 +870,7 @@ static struct kvm_memslots *kvm_alloc_memslots(void)
 	if (!slots)
 		return NULL;
 
+	slots->hva_tree = RB_ROOT_CACHED;
 	hash_init(slots->id_hash);
 
 	return slots;
@@ -1262,22 +1274,32 @@ static void kvm_replace_memslot(struct kvm_memslots *slots,
 				struct kvm_memory_slot *new)
 {
 	/*
-	 * Remove the old memslot from the hash list, copying the node data
-	 * would corrupt the list.
+	 * Remove the old memslot from the hash list and interval tree, copying
+	 * the node data would corrupt the structures.
 	 */
 	if (old) {
 		hash_del(&old->id_node);
+		interval_tree_remove(&old->hva_node, &slots->hva_tree);
 
 		if (!new)
 			return;
 	}
 
-	/* Copy the source *data*, not the pointer, to the destination. */
-	if (old)
+	/*
+	 * Copy the source *data*, not the pointer, to the destination.  If
+	 * @old is NULL, initialize @new's hva range.
+	 */
+	if (old) {
 		*new = *old;
+	} else if (new) {
+		new->hva_node.start = new->userspace_addr;
+		new->hva_node.last = new->userspace_addr +
+				     (new->npages << PAGE_SHIFT) - 1;
+	}
 
 	/* (Re)Add the new memslot. */
 	hash_add(slots->id_hash, &new->id_node, new->id);
+	interval_tree_insert(&new->hva_node, &slots->hva_tree);
 }
 
 static void kvm_shift_memslot(struct kvm_memslots *slots, int dst, int src)
@@ -1308,7 +1330,7 @@ static inline void kvm_memslot_delete(struct kvm_memslots *slots,
 		atomic_set(&slots->last_used_slot, 0);
 
 	/*
-	 * Remove the to-be-deleted memslot from the list _before_ shifting
+	 * Remove the to-be-deleted memslot from the list/tree _before_ shifting
 	 * the trailing memslots forward, its data will be overwritten.
 	 * Defer the (somewhat pointless) copying of the memslot until after
 	 * the last slot has been shifted to avoid overwriting said last slot.
@@ -1335,7 +1357,8 @@ static inline int kvm_memslot_insert_back(struct kvm_memslots *slots)
  * itself is not preserved in the array, i.e. not swapped at this time, only
  * its new index into the array is tracked.  Returns the changed memslot's
  * current index into the memslots array.
- * The memslot at the returned index will not be in @slots->id_hash by then.
+ * The memslot at the returned index will not be in @slots->hva_tree or
+ * @slots->id_hash by then.
  * @memslot is a detached struct with desired final data of the changed slot.
  */
 static inline int kvm_memslot_move_backward(struct kvm_memslots *slots,
@@ -1349,10 +1372,10 @@ static inline int kvm_memslot_move_backward(struct kvm_memslots *slots,
 		return -1;
 
 	/*
-	 * Delete the slot from the hash table before sorting the remaining
-	 * slots, the slot's data may be overwritten when copying slots as part
-	 * of the sorting proccess.  update_memslots() will unconditionally
-	 * rewrite the entire slot and re-add it to the hash table.
+	 * Delete the slot from the hash table and interval tree before sorting
+	 * the remaining slots, the slot's data may be overwritten when copying
+	 * slots as part of the sorting proccess.  update_memslots() will
+	 * unconditionally rewrite and re-add the entire slot.
 	 */
 	kvm_replace_memslot(slots, oldslot, NULL);
 
@@ -1378,10 +1401,12 @@ static inline int kvm_memslot_move_backward(struct kvm_memslots *slots,
  * is not preserved in the array, i.e. not swapped at this time, only its new
  * index into the array is tracked.  Returns the changed memslot's final index
  * into the memslots array.
- * The memslot at the returned index will not be in @slots->id_hash by then.
+ * The memslot at the returned index will not be in @slots->hva_tree or
+ * @slots->id_hash by then.
  * @memslot is a detached struct with desired final data of the new or
  * changed slot.
- * Assumes that the memslot at @start index is not in @slots->id_hash.
+ * Assumes that the memslot at @start index is not in @slots->hva_tree or
+ * @slots->id_hash.
  */
 static inline int kvm_memslot_move_forward(struct kvm_memslots *slots,
 					   struct kvm_memory_slot *memslot,
@@ -1574,9 +1599,12 @@ static struct kvm_memslots *kvm_dup_memslots(struct kvm_memslots *old,
 
 	memcpy(slots, old, kvm_memslots_size(old->used_slots));
 
+	slots->hva_tree = RB_ROOT_CACHED;
 	hash_init(slots->id_hash);
-	kvm_for_each_memslot(memslot, slots)
+	kvm_for_each_memslot(memslot, slots) {
+		interval_tree_insert(&memslot->hva_node, &slots->hva_tree);
 		hash_add(slots->id_hash, &memslot->id_node, memslot->id);
+	}
 
 	return slots;
 }
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 24/30] KVM: Use interval tree to do fast hva lookup in memslots

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> 
> The current memslots implementation only allows quick binary search by gfn,
> quick lookup by hva is not possible - the implementation has to do a linear
> scan of the whole memslots array, even though the operation being performed
> might apply just to a single memslot.
> 
> This significantly hurts performance of per-hva operations with higher
> memslot counts.
> 
> Since hva ranges can overlap between memslots an interval tree is needed
> for tracking them.
> 
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> [sean: handle interval tree updates in kvm_replace_memslot()]
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   arch/arm64/kvm/Kconfig   |  1 +
>   arch/mips/kvm/Kconfig    |  1 +
>   arch/powerpc/kvm/Kconfig |  1 +
>   arch/s390/kvm/Kconfig    |  1 +
>   arch/x86/kvm/Kconfig     |  1 +
>   include/linux/kvm_host.h |  3 ++
>   virt/kvm/kvm_main.c      | 60 +++++++++++++++++++++++++++++-----------
>   7 files changed, 52 insertions(+), 16 deletions(-)
> 
(..)
> @@ -1262,22 +1274,32 @@ static void kvm_replace_memslot(struct kvm_memslots *slots,
>   				struct kvm_memory_slot *new)
>   {
>   	/*
> -	 * Remove the old memslot from the hash list, copying the node data
> -	 * would corrupt the list.
> +	 * Remove the old memslot from the hash list and interval tree, copying
> +	 * the node data would corrupt the structures.
>   	 */
>   	if (old) {
>   		hash_del(&old->id_node);
> +		interval_tree_remove(&old->hva_node, &slots->hva_tree);
>   
>   		if (!new)
>   			return;
>   	}
>   
> -	/* Copy the source *data*, not the pointer, to the destination. */
> -	if (old)
> +	/*
> +	 * Copy the source *data*, not the pointer, to the destination.  If
> +	 * @old is NULL, initialize @new's hva range.
> +	 */
> +	if (old) {
>   		*new = *old;
> +	} else if (new) {

Unnecessary check - if "new" is NULL then the code will crash anyway
accessing this pointer unconditionally...

> +		new->hva_node.start = new->userspace_addr;
> +		new->hva_node.last = new->userspace_addr +
> +				     (new->npages << PAGE_SHIFT) - 1;
> +	}
>   
>   	/* (Re)Add the new memslot. */
>   	hash_add(slots->id_hash, &new->id_node, new->id);
> +	interval_tree_insert(&new->hva_node, &slots->hva_tree);

...in these two lines above.

Thanks,
Maciej

Re: [PATCH v5.5 24/30] KVM: Use interval tree to do fast hva lookup in memslots

[Sean Christopherson]

On Fri, Nov 12, 2021, Maciej S. Szmigiero wrote:
> On 04.11.2021 01:25, Sean Christopherson wrote:
> > @@ -1262,22 +1274,32 @@ static void kvm_replace_memslot(struct kvm_memslots *slots,
> >   				struct kvm_memory_slot *new)
> >   {
> >   	/*
> > -	 * Remove the old memslot from the hash list, copying the node data
> > -	 * would corrupt the list.
> > +	 * Remove the old memslot from the hash list and interval tree, copying
> > +	 * the node data would corrupt the structures.
> >   	 */
> >   	if (old) {
> >   		hash_del(&old->id_node);
> > +		interval_tree_remove(&old->hva_node, &slots->hva_tree);
> >   		if (!new)
> >   			return;
> >   	}
> > -	/* Copy the source *data*, not the pointer, to the destination. */
> > -	if (old)
> > +	/*
> > +	 * Copy the source *data*, not the pointer, to the destination.  If
> > +	 * @old is NULL, initialize @new's hva range.
> > +	 */
> > +	if (old) {
> >   		*new = *old;
> > +	} else if (new) {
> 
> Unnecessary check - if "new" is NULL then the code will crash anyway
> accessing this pointer unconditionally...
> 
> > +		new->hva_node.start = new->userspace_addr;
> > +		new->hva_node.last = new->userspace_addr +
> > +				     (new->npages << PAGE_SHIFT) - 1;
> > +	}
> >   	/* (Re)Add the new memslot. */
> >   	hash_add(slots->id_hash, &new->id_node, new->id);
> > +	interval_tree_insert(&new->hva_node, &slots->hva_tree);
> 
> ...in these two lines above.

Yep, definitely worthless.  I think this was another "plan for the future" idea
that didn't actually add value.

[PATCH v5.5 25/30] KVM: s390: Introduce kvm_s390_get_gfn_end()

[Sean Christopherson]

From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

And use it where s390 code would just access the memslot with the highest
gfn directly.

No functional change intended.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/s390/kvm/kvm-s390.c |  2 +-
 arch/s390/kvm/kvm-s390.h | 12 ++++++++++++
 arch/s390/kvm/pv.c       |  4 +---
 3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 4e032e176216..f7cc0853866b 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2012,7 +2012,7 @@ static int kvm_s390_get_cmma(struct kvm *kvm, struct kvm_s390_cmma_log *args,
 	if (!ms)
 		return 0;
 	next_gfn = kvm_s390_next_dirty_cmma(slots, cur_gfn + 1);
-	mem_end = slots->memslots[0].base_gfn + slots->memslots[0].npages;
+	mem_end = kvm_s390_get_gfn_end(slots);
 
 	while (args->count < bufsize) {
 		hva = gfn_to_hva(kvm, cur_gfn);
diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
index 52bc8fbaa60a..207d299d7fea 100644
--- a/arch/s390/kvm/kvm-s390.h
+++ b/arch/s390/kvm/kvm-s390.h
@@ -208,6 +208,18 @@ static inline int kvm_s390_user_cpu_state_ctrl(struct kvm *kvm)
 	return kvm->arch.user_cpu_state_ctrl != 0;
 }
 
+/* get the end gfn of the last (highest gfn) memslot */
+static inline unsigned long kvm_s390_get_gfn_end(struct kvm_memslots *slots)
+{
+	struct kvm_memory_slot *ms;
+
+	if (WARN_ON(!slots->used_slots))
+		return 0;
+
+	ms = slots->memslots;
+	return ms->base_gfn + ms->npages;
+}
+
 /* implemented in pv.c */
 int kvm_s390_pv_destroy_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc);
 int kvm_s390_pv_create_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc);
diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
index c8841f476e91..e51cccfded25 100644
--- a/arch/s390/kvm/pv.c
+++ b/arch/s390/kvm/pv.c
@@ -117,7 +117,6 @@ static int kvm_s390_pv_alloc_vm(struct kvm *kvm)
 	unsigned long base = uv_info.guest_base_stor_len;
 	unsigned long virt = uv_info.guest_virt_var_stor_len;
 	unsigned long npages = 0, vlen = 0;
-	struct kvm_memory_slot *memslot;
 
 	kvm->arch.pv.stor_var = NULL;
 	kvm->arch.pv.stor_base = __get_free_pages(GFP_KERNEL_ACCOUNT, get_order(base));
@@ -131,8 +130,7 @@ static int kvm_s390_pv_alloc_vm(struct kvm *kvm)
 	 * Slots are sorted by GFN
 	 */
 	mutex_lock(&kvm->slots_lock);
-	memslot = kvm_memslots(kvm)->memslots;
-	npages = memslot->base_gfn + memslot->npages;
+	npages = kvm_s390_get_gfn_end(kvm_memslots(kvm));
 	mutex_unlock(&kvm->slots_lock);
 
 	kvm->arch.pv.guest_len = npages * PAGE_SIZE;
-- 
2.33.1.1089.g2158813163f-goog

[PATCH v5.5 26/30] KVM: Keep memslots in tree-based structures instead of array-based ones

[Sean Christopherson]

From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

The current memslot code uses a (reverse gfn-ordered) memslot array for
keeping track of them.

Because the memslot array that is currently in use cannot be modified
every memslot management operation (create, delete, move, change flags)
has to make a copy of the whole array so it has a scratch copy to work on.

Strictly speaking, however, it is only necessary to make copy of the
memslot that is being modified, copying all the memslots currently present
is just a limitation of the array-based memslot implementation.

Two memslot sets, however, are still needed so the VM continues to run
on the currently active set while the requested operation is being
performed on the second, currently inactive one.

In order to have two memslot sets, but only one copy of actual memslots
it is necessary to split out the memslot data from the memslot sets.

The memslots themselves should be also kept independent of each other
so they can be individually added or deleted.

These two memslot sets should normally point to the same set of
memslots. They can, however, be desynchronized when performing a
memslot management operation by replacing the memslot to be modified
by its copy.  After the operation is complete, both memslot sets once
again point to the same, common set of memslot data.

This commit implements the aforementioned idea.

For tracking of gfns an ordinary rbtree is used since memslots cannot
overlap in the guest address space and so this data structure is
sufficient for ensuring that lookups are done quickly.

The "last used slot" mini-caches (both per-slot set one and per-vCPU one),
that keep track of the last found-by-gfn memslot, are still present in the
new code.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/arm64/kvm/mmu.c                |   8 +-
 arch/powerpc/kvm/book3s_64_mmu_hv.c |   4 +-
 arch/powerpc/kvm/book3s_hv.c        |   3 +-
 arch/powerpc/kvm/book3s_hv_nested.c |   4 +-
 arch/powerpc/kvm/book3s_hv_uvmem.c  |  14 +-
 arch/s390/kvm/kvm-s390.c            |  24 +-
 arch/s390/kvm/kvm-s390.h            |   6 +-
 arch/x86/kvm/debugfs.c              |   6 +-
 arch/x86/kvm/mmu/mmu.c              |   8 +-
 include/linux/kvm_host.h            | 141 +++--
 virt/kvm/kvm_main.c                 | 809 ++++++++++++++--------------
 11 files changed, 524 insertions(+), 503 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index a76718388cbd..c27f472b4d24 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -210,13 +210,13 @@ static void stage2_flush_vm(struct kvm *kvm)
 {
 	struct kvm_memslots *slots;
 	struct kvm_memory_slot *memslot;
-	int idx;
+	int idx, bkt;
 
 	idx = srcu_read_lock(&kvm->srcu);
 	spin_lock(&kvm->mmu_lock);
 
 	slots = kvm_memslots(kvm);
-	kvm_for_each_memslot(memslot, slots)
+	kvm_for_each_memslot(memslot, bkt, slots)
 		stage2_flush_memslot(kvm, memslot);
 
 	spin_unlock(&kvm->mmu_lock);
@@ -595,14 +595,14 @@ void stage2_unmap_vm(struct kvm *kvm)
 {
 	struct kvm_memslots *slots;
 	struct kvm_memory_slot *memslot;
-	int idx;
+	int idx, bkt;
 
 	idx = srcu_read_lock(&kvm->srcu);
 	mmap_read_lock(current->mm);
 	spin_lock(&kvm->mmu_lock);
 
 	slots = kvm_memslots(kvm);
-	kvm_for_each_memslot(memslot, slots)
+	kvm_for_each_memslot(memslot, bkt, slots)
 		stage2_unmap_memslot(kvm, memslot);
 
 	spin_unlock(&kvm->mmu_lock);
diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
index c63e263312a4..213232914367 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -734,11 +734,11 @@ void kvmppc_rmap_reset(struct kvm *kvm)
 {
 	struct kvm_memslots *slots;
 	struct kvm_memory_slot *memslot;
-	int srcu_idx;
+	int srcu_idx, bkt;
 
 	srcu_idx = srcu_read_lock(&kvm->srcu);
 	slots = kvm_memslots(kvm);
-	kvm_for_each_memslot(memslot, slots) {
+	kvm_for_each_memslot(memslot, bkt, slots) {
 		/* Mutual exclusion with kvm_unmap_hva_range etc. */
 		spin_lock(&kvm->mmu_lock);
 		/*
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 4d40c1867be5..2a97363c9a31 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -5854,11 +5854,12 @@ static int kvmhv_svm_off(struct kvm *kvm)
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
 		struct kvm_memory_slot *memslot;
 		struct kvm_memslots *slots = __kvm_memslots(kvm, i);
+		int bkt;
 
 		if (!slots)
 			continue;
 
-		kvm_for_each_memslot(memslot, slots) {
+		kvm_for_each_memslot(memslot, bkt, slots) {
 			kvmppc_uvmem_drop_pages(memslot, kvm, true);
 			uv_unregister_mem_slot(kvm->arch.lpid, memslot->id);
 		}
diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
index ed8a2c9f5629..9435e482d514 100644
--- a/arch/powerpc/kvm/book3s_hv_nested.c
+++ b/arch/powerpc/kvm/book3s_hv_nested.c
@@ -749,7 +749,7 @@ void kvmhv_release_all_nested(struct kvm *kvm)
 	struct kvm_nested_guest *gp;
 	struct kvm_nested_guest *freelist = NULL;
 	struct kvm_memory_slot *memslot;
-	int srcu_idx;
+	int srcu_idx, bkt;
 
 	spin_lock(&kvm->mmu_lock);
 	for (i = 0; i <= kvm->arch.max_nested_lpid; i++) {
@@ -770,7 +770,7 @@ void kvmhv_release_all_nested(struct kvm *kvm)
 	}
 
 	srcu_idx = srcu_read_lock(&kvm->srcu);
-	kvm_for_each_memslot(memslot, kvm_memslots(kvm))
+	kvm_for_each_memslot(memslot, bkt, kvm_memslots(kvm))
 		kvmhv_free_memslot_nest_rmap(memslot);
 	srcu_read_unlock(&kvm->srcu, srcu_idx);
 }
diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
index a7061ee3b157..adc1c495d47c 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -459,7 +459,7 @@ unsigned long kvmppc_h_svm_init_start(struct kvm *kvm)
 	struct kvm_memslots *slots;
 	struct kvm_memory_slot *memslot, *m;
 	int ret = H_SUCCESS;
-	int srcu_idx;
+	int srcu_idx, bkt;
 
 	kvm->arch.secure_guest = KVMPPC_SECURE_INIT_START;
 
@@ -478,7 +478,7 @@ unsigned long kvmppc_h_svm_init_start(struct kvm *kvm)
 
 	/* register the memslot */
 	slots = kvm_memslots(kvm);
-	kvm_for_each_memslot(memslot, slots) {
+	kvm_for_each_memslot(memslot, bkt, slots) {
 		ret = __kvmppc_uvmem_memslot_create(kvm, memslot);
 		if (ret)
 			break;
@@ -486,7 +486,7 @@ unsigned long kvmppc_h_svm_init_start(struct kvm *kvm)
 
 	if (ret) {
 		slots = kvm_memslots(kvm);
-		kvm_for_each_memslot(m, slots) {
+		kvm_for_each_memslot(m, bkt, slots) {
 			if (m == memslot)
 				break;
 			__kvmppc_uvmem_memslot_delete(kvm, memslot);
@@ -647,7 +647,7 @@ void kvmppc_uvmem_drop_pages(const struct kvm_memory_slot *slot,
 
 unsigned long kvmppc_h_svm_init_abort(struct kvm *kvm)
 {
-	int srcu_idx;
+	int srcu_idx, bkt;
 	struct kvm_memory_slot *memslot;
 
 	/*
@@ -662,7 +662,7 @@ unsigned long kvmppc_h_svm_init_abort(struct kvm *kvm)
 
 	srcu_idx = srcu_read_lock(&kvm->srcu);
 
-	kvm_for_each_memslot(memslot, kvm_memslots(kvm))
+	kvm_for_each_memslot(memslot, bkt, kvm_memslots(kvm))
 		kvmppc_uvmem_drop_pages(memslot, kvm, false);
 
 	srcu_read_unlock(&kvm->srcu, srcu_idx);
@@ -821,7 +821,7 @@ unsigned long kvmppc_h_svm_init_done(struct kvm *kvm)
 {
 	struct kvm_memslots *slots;
 	struct kvm_memory_slot *memslot;
-	int srcu_idx;
+	int srcu_idx, bkt;
 	long ret = H_SUCCESS;
 
 	if (!(kvm->arch.secure_guest & KVMPPC_SECURE_INIT_START))
@@ -830,7 +830,7 @@ unsigned long kvmppc_h_svm_init_done(struct kvm *kvm)
 	/* migrate any unmoved normal pfn to device pfns*/
 	srcu_idx = srcu_read_lock(&kvm->srcu);
 	slots = kvm_memslots(kvm);
-	kvm_for_each_memslot(memslot, slots) {
+	kvm_for_each_memslot(memslot, bkt, slots) {
 		ret = kvmppc_uv_migrate_mem_slot(kvm, memslot);
 		if (ret) {
 			/*
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index f7cc0853866b..f2c12456a047 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1035,13 +1035,13 @@ static int kvm_s390_vm_start_migration(struct kvm *kvm)
 	struct kvm_memory_slot *ms;
 	struct kvm_memslots *slots;
 	unsigned long ram_pages = 0;
-	int slotnr;
+	int bkt;
 
 	/* migration mode already enabled */
 	if (kvm->arch.migration_mode)
 		return 0;
 	slots = kvm_memslots(kvm);
-	if (!slots || !slots->used_slots)
+	if (!slots || kvm_memslots_empty(slots))
 		return -EINVAL;
 
 	if (!kvm->arch.use_cmma) {
@@ -1049,8 +1049,7 @@ static int kvm_s390_vm_start_migration(struct kvm *kvm)
 		return 0;
 	}
 	/* mark all the pages in active slots as dirty */
-	for (slotnr = 0; slotnr < slots->used_slots; slotnr++) {
-		ms = slots->memslots + slotnr;
+	kvm_for_each_memslot(ms, bkt, slots) {
 		if (!ms->dirty_bitmap)
 			return -EINVAL;
 		/*
@@ -1974,22 +1973,21 @@ static unsigned long kvm_s390_next_dirty_cmma(struct kvm_memslots *slots,
 					      unsigned long cur_gfn)
 {
 	struct kvm_memory_slot *ms = gfn_to_memslot_approx(slots, cur_gfn);
-	int slotidx = ms - slots->memslots;
 	unsigned long ofs = cur_gfn - ms->base_gfn;
+	struct rb_node *mnode = &ms->gfn_node[slots->node_idx];
 
 	if (ms->base_gfn + ms->npages <= cur_gfn) {
-		slotidx--;
+		mnode = rb_next(mnode);
 		/* If we are above the highest slot, wrap around */
-		if (slotidx < 0)
-			slotidx = slots->used_slots - 1;
+		if (!mnode)
+			mnode = rb_first(&slots->gfn_tree);
 
-		ms = slots->memslots + slotidx;
+		ms = container_of(mnode, struct kvm_memory_slot, gfn_node[slots->node_idx]);
 		ofs = 0;
 	}
 	ofs = find_next_bit(kvm_second_dirty_bitmap(ms), ms->npages, ofs);
-	while ((slotidx > 0) && (ofs >= ms->npages)) {
-		slotidx--;
-		ms = slots->memslots + slotidx;
+	while (ofs >= ms->npages && (mnode = rb_next(mnode))) {
+		ms = container_of(mnode, struct kvm_memory_slot, gfn_node[slots->node_idx]);
 		ofs = find_next_bit(kvm_second_dirty_bitmap(ms), ms->npages, 0);
 	}
 	return ms->base_gfn + ofs;
@@ -2002,7 +2000,7 @@ static int kvm_s390_get_cmma(struct kvm *kvm, struct kvm_s390_cmma_log *args,
 	struct kvm_memslots *slots = kvm_memslots(kvm);
 	struct kvm_memory_slot *ms;
 
-	if (unlikely(!slots->used_slots))
+	if (unlikely(kvm_memslots_empty(slots)))
 		return 0;
 
 	cur_gfn = kvm_s390_next_dirty_cmma(slots, args->start_gfn);
diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
index 207d299d7fea..a8769c1b5cec 100644
--- a/arch/s390/kvm/kvm-s390.h
+++ b/arch/s390/kvm/kvm-s390.h
@@ -211,12 +211,14 @@ static inline int kvm_s390_user_cpu_state_ctrl(struct kvm *kvm)
 /* get the end gfn of the last (highest gfn) memslot */
 static inline unsigned long kvm_s390_get_gfn_end(struct kvm_memslots *slots)
 {
+	struct rb_node *node;
 	struct kvm_memory_slot *ms;
 
-	if (WARN_ON(!slots->used_slots))
+	if (WARN_ON(kvm_memslots_empty(slots)))
 		return 0;
 
-	ms = slots->memslots;
+	node = rb_last(&slots->gfn_tree);
+	ms = container_of(node, struct kvm_memory_slot, gfn_node[slots->node_idx]);
 	return ms->base_gfn + ms->npages;
 }
 
diff --git a/arch/x86/kvm/debugfs.c b/arch/x86/kvm/debugfs.c
index 54a83a744538..543a8c04025c 100644
--- a/arch/x86/kvm/debugfs.c
+++ b/arch/x86/kvm/debugfs.c
@@ -107,9 +107,10 @@ static int kvm_mmu_rmaps_stat_show(struct seq_file *m, void *v)
 	write_lock(&kvm->mmu_lock);
 
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
+		int bkt;
+
 		slots = __kvm_memslots(kvm, i);
-		for (j = 0; j < slots->used_slots; j++) {
-			slot = &slots->memslots[j];
+		kvm_for_each_memslot(slot, bkt, slots)
 			for (k = 0; k < KVM_NR_PAGE_SIZES; k++) {
 				rmap = slot->arch.rmap[k];
 				lpage_size = kvm_mmu_slot_lpages(slot, k + 1);
@@ -121,7 +122,6 @@ static int kvm_mmu_rmaps_stat_show(struct seq_file *m, void *v)
 					cur[index]++;
 				}
 			}
-		}
 	}
 
 	write_unlock(&kvm->mmu_lock);
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 564781585fd2..09ff0ccaa203 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3405,7 +3405,7 @@ static int mmu_first_shadow_root_alloc(struct kvm *kvm)
 {
 	struct kvm_memslots *slots;
 	struct kvm_memory_slot *slot;
-	int r = 0, i;
+	int r = 0, i, bkt;
 
 	/*
 	 * Check if this is the first shadow root being allocated before
@@ -3430,7 +3430,7 @@ static int mmu_first_shadow_root_alloc(struct kvm *kvm)
 
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
 		slots = __kvm_memslots(kvm, i);
-		kvm_for_each_memslot(slot, slots) {
+		kvm_for_each_memslot(slot, bkt, slots) {
 			/*
 			 * Both of these functions are no-ops if the target is
 			 * already allocated, so unconditionally calling both
@@ -5716,14 +5716,14 @@ static bool __kvm_zap_rmaps(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
 	struct kvm_memslots *slots;
 	bool flush = false;
 	gfn_t start, end;
-	int i;
+	int i, bkt;
 
 	if (!kvm_memslots_have_rmaps(kvm))
 		return flush;
 
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
 		slots = __kvm_memslots(kvm, i);
-		kvm_for_each_memslot(memslot, slots) {
+		kvm_for_each_memslot(memslot, bkt, slots) {
 			start = max(gfn_start, memslot->base_gfn);
 			end = min(gfn_end, memslot->base_gfn + memslot->npages);
 			if (start >= end)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index d0363e2ba098..6888f3c2e04b 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -31,6 +31,7 @@
 #include <linux/notifier.h>
 #include <linux/hashtable.h>
 #include <linux/interval_tree.h>
+#include <linux/rbtree.h>
 #include <asm/signal.h>
 
 #include <linux/kvm.h>
@@ -357,11 +358,13 @@ struct kvm_vcpu {
 	struct kvm_dirty_ring dirty_ring;
 
 	/*
-	 * The index of the most recently used memslot by this vCPU. It's ok
-	 * if this becomes stale due to memslot changes since we always check
-	 * it is a valid slot.
+	 * The most recently used memslot by this vCPU and the slots generation
+	 * for which it is valid.
+	 * No wraparound protection is needed since generations won't overflow in
+	 * thousands of years, even assuming 1M memslot operations per second.
 	 */
-	int last_used_slot;
+	struct kvm_memory_slot *last_used_slot;
+	u64 last_used_slot_gen;
 };
 
 /* must be called with irqs disabled */
@@ -426,9 +429,26 @@ static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)
  */
 #define KVM_MEM_MAX_NR_PAGES ((1UL << 31) - 1)
 
+/*
+ * Since at idle each memslot belongs to two memslot sets it has to contain
+ * two embedded nodes for each data structure that it forms a part of.
+ *
+ * Two memslot sets (one active and one inactive) are necessary so the VM
+ * continues to run on one memslot set while the other is being modified.
+ *
+ * These two memslot sets normally point to the same set of memslots.
+ * They can, however, be desynchronized when performing a memslot management
+ * operation by replacing the memslot to be modified by its copy.
+ * After the operation is complete, both memslot sets once again point to
+ * the same, common set of memslot data.
+ *
+ * The memslots themselves are independent of each other so they can be
+ * individually added or deleted.
+ */
 struct kvm_memory_slot {
-	struct hlist_node id_node;
-	struct interval_tree_node hva_node;
+	struct hlist_node id_node[2];
+	struct interval_tree_node hva_node[2];
+	struct rb_node gfn_node[2];
 	gfn_t base_gfn;
 	unsigned long npages;
 	unsigned long *dirty_bitmap;
@@ -523,19 +543,14 @@ static inline int kvm_arch_vcpu_memslots_id(struct kvm_vcpu *vcpu)
 }
 #endif
 
-/*
- * Note:
- * memslots are not sorted by id anymore, please use id_to_memslot()
- * to get the memslot by its id.
- */
 struct kvm_memslots {
 	u64 generation;
+	atomic_long_t last_used_slot;
 	struct rb_root_cached hva_tree;
-	/* The mapping table from slot id to the index in memslots[]. */
+	struct rb_root gfn_tree;
+	/* The mapping table from slot id to memslot. */
 	DECLARE_HASHTABLE(id_hash, 7);
-	atomic_t last_used_slot;
-	int used_slots;
-	struct kvm_memory_slot memslots[];
+	int node_idx;
 };
 
 struct kvm {
@@ -557,6 +572,9 @@ struct kvm {
 	struct mutex slots_arch_lock;
 	struct mm_struct *mm; /* userspace tied to this vm */
 	unsigned long nr_memslot_pages;
+	/* The two memslot sets - active and inactive (per address space) */
+	struct kvm_memslots __memslots[KVM_ADDRESS_SPACE_NUM][2];
+	/* The current active memslot set for each address space */
 	struct kvm_memslots __rcu *memslots[KVM_ADDRESS_SPACE_NUM];
 	struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
 
@@ -725,11 +743,10 @@ static inline struct kvm_vcpu *kvm_get_vcpu_by_id(struct kvm *kvm, int id)
 	return NULL;
 }
 
-#define kvm_for_each_memslot(memslot, slots)				\
-	for (memslot = &slots->memslots[0];				\
-	     memslot < slots->memslots + slots->used_slots; memslot++)	\
-		if (WARN_ON_ONCE(!memslot->npages)) {			\
-		} else
+static inline int kvm_vcpu_get_idx(struct kvm_vcpu *vcpu)
+{
+	return vcpu->vcpu_idx;
+}
 
 void kvm_vcpu_destroy(struct kvm_vcpu *vcpu);
 
@@ -791,12 +808,23 @@ static inline struct kvm_memslots *kvm_vcpu_memslots(struct kvm_vcpu *vcpu)
 	return __kvm_memslots(vcpu->kvm, as_id);
 }
 
+static inline bool kvm_memslots_empty(struct kvm_memslots *slots)
+{
+	return RB_EMPTY_ROOT(&slots->gfn_tree);
+}
+
+#define kvm_for_each_memslot(memslot, bkt, slots)			      \
+	hash_for_each(slots->id_hash, bkt, memslot, id_node[slots->node_idx]) \
+		if (WARN_ON_ONCE(!memslot->npages)) {			      \
+		} else
+
 static inline
 struct kvm_memory_slot *id_to_memslot(struct kvm_memslots *slots, int id)
 {
 	struct kvm_memory_slot *slot;
+	int idx = slots->node_idx;
 
-	hash_for_each_possible(slots->id_hash, slot, id_node, id) {
+	hash_for_each_possible(slots->id_hash, slot, id_node[idx], id) {
 		if (slot->id == id)
 			return slot;
 	}
@@ -1204,25 +1232,15 @@ void kvm_free_irq_source_id(struct kvm *kvm, int irq_source_id);
 bool kvm_arch_irqfd_allowed(struct kvm *kvm, struct kvm_irqfd *args);
 
 /*
- * Returns a pointer to the memslot at slot_index if it contains gfn.
+ * Returns a pointer to the memslot if it contains gfn.
  * Otherwise returns NULL.
  */
 static inline struct kvm_memory_slot *
-try_get_memslot(struct kvm_memslots *slots, int slot_index, gfn_t gfn)
+try_get_memslot(struct kvm_memory_slot *slot, gfn_t gfn)
 {
-	struct kvm_memory_slot *slot;
-
-	if (slot_index < 0 || slot_index >= slots->used_slots)
+	if (!slot)
 		return NULL;
 
-	/*
-	 * slot_index can come from vcpu->last_used_slot which is not kept
-	 * in sync with userspace-controllable memslot deletion. So use nospec
-	 * to prevent the CPU from speculating past the end of memslots[].
-	 */
-	slot_index = array_index_nospec(slot_index, slots->used_slots);
-	slot = &slots->memslots[slot_index];
-
 	if (gfn >= slot->base_gfn && gfn < slot->base_gfn + slot->npages)
 		return slot;
 	else
@@ -1230,65 +1248,46 @@ try_get_memslot(struct kvm_memslots *slots, int slot_index, gfn_t gfn)
 }
 
 /*
- * Returns a pointer to the memslot that contains gfn and records the index of
- * the slot in index. Otherwise returns NULL.
+ * Returns a pointer to the memslot that contains gfn. Otherwise returns NULL.
  *
  * With "approx" set returns the memslot also when the address falls
  * in a hole. In that case one of the memslots bordering the hole is
  * returned.
- *
- * IMPORTANT: Slots are sorted from highest GFN to lowest GFN!
  */
 static inline struct kvm_memory_slot *
-search_memslots(struct kvm_memslots *slots, gfn_t gfn, int *index, bool approx)
+search_memslots(struct kvm_memslots *slots, gfn_t gfn, bool approx)
 {
-	int start = 0, end = slots->used_slots;
-	struct kvm_memory_slot *memslots = slots->memslots;
 	struct kvm_memory_slot *slot;
+	struct rb_node *node;
+	int idx = slots->node_idx;
 
-	if (unlikely(!slots->used_slots))
-		return NULL;
-
-	while (start < end) {
-		int slot = start + (end - start) / 2;
-
-		if (gfn >= memslots[slot].base_gfn)
-			end = slot;
-		else
-			start = slot + 1;
-	}
-
-	if (approx && start >= slots->used_slots) {
-		*index = slots->used_slots - 1;
-		return &memslots[slots->used_slots - 1];
-	}
-
-	slot = try_get_memslot(slots, start, gfn);
-	if (slot) {
-		*index = start;
-		return slot;
-	}
-	if (approx) {
-		*index = start;
-		return &memslots[start];
+	slot = NULL;
+	for (node = slots->gfn_tree.rb_node; node; ) {
+		slot = container_of(node, struct kvm_memory_slot, gfn_node[idx]);
+		if (gfn >= slot->base_gfn) {
+			if (gfn < slot->base_gfn + slot->npages)
+				return slot;
+			node = node->rb_right;
+		} else
+			node = node->rb_left;
 	}
 
-	return NULL;
+	return approx ? slot : NULL;
 }
 
 static inline struct kvm_memory_slot *
 ____gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn, bool approx)
 {
 	struct kvm_memory_slot *slot;
-	int slot_index = atomic_read(&slots->last_used_slot);
 
-	slot = try_get_memslot(slots, slot_index, gfn);
+	slot = (struct kvm_memory_slot *)atomic_long_read(&slots->last_used_slot);
+	slot = try_get_memslot(slot, gfn);
 	if (slot)
 		return slot;
 
-	slot = search_memslots(slots, gfn, &slot_index, approx);
+	slot = search_memslots(slots, gfn, approx);
 	if (slot) {
-		atomic_set(&slots->last_used_slot, slot_index);
+		atomic_long_set(&slots->last_used_slot, (unsigned long)slot);
 		return slot;
 	}
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f2235c430e64..d095e01838bf 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -432,7 +432,7 @@ static void kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
 	vcpu->preempted = false;
 	vcpu->ready = false;
 	preempt_notifier_init(&vcpu->preempt_notifier, &kvm_preempt_ops);
-	vcpu->last_used_slot = 0;
+	vcpu->last_used_slot = NULL;
 }
 
 void kvm_vcpu_destroy(struct kvm_vcpu *vcpu)
@@ -531,7 +531,7 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
 						  range->start, range->end - 1) {
 			unsigned long hva_start, hva_end;
 
-			slot = container_of(node, struct kvm_memory_slot, hva_node);
+			slot = container_of(node, struct kvm_memory_slot, hva_node[slots->node_idx]);
 			hva_start = max(range->start, slot->userspace_addr);
 			hva_end = min(range->end, slot->userspace_addr +
 						  (slot->npages << PAGE_SHIFT));
@@ -862,20 +862,6 @@ static void kvm_destroy_pm_notifier(struct kvm *kvm)
 }
 #endif /* CONFIG_HAVE_KVM_PM_NOTIFIER */
 
-static struct kvm_memslots *kvm_alloc_memslots(void)
-{
-	struct kvm_memslots *slots;
-
-	slots = kvzalloc(sizeof(struct kvm_memslots), GFP_KERNEL_ACCOUNT);
-	if (!slots)
-		return NULL;
-
-	slots->hva_tree = RB_ROOT_CACHED;
-	hash_init(slots->id_hash);
-
-	return slots;
-}
-
 static void kvm_destroy_dirty_bitmap(struct kvm_memory_slot *memslot)
 {
 	if (!memslot->dirty_bitmap)
@@ -885,27 +871,33 @@ static void kvm_destroy_dirty_bitmap(struct kvm_memory_slot *memslot)
 	memslot->dirty_bitmap = NULL;
 }
 
+/* This does not remove the slot from struct kvm_memslots data structures */
 static void kvm_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
 {
 	kvm_destroy_dirty_bitmap(slot);
 
 	kvm_arch_free_memslot(kvm, slot);
 
-	slot->flags = 0;
-	slot->npages = 0;
+	kfree(slot);
 }
 
 static void kvm_free_memslots(struct kvm *kvm, struct kvm_memslots *slots)
 {
+	struct hlist_node *idnode;
 	struct kvm_memory_slot *memslot;
+	int bkt;
 
-	if (!slots)
+	/*
+	 * The same memslot objects live in both active and inactive sets,
+	 * arbitrarily free using index '1' so the second invocation of this
+	 * function isn't operating over a structure with dangling pointers
+	 * (even though this function isn't actually touching them).
+	 */
+	if (!slots->node_idx)
 		return;
 
-	kvm_for_each_memslot(memslot, slots)
+	hash_for_each_safe(slots->id_hash, bkt, idnode, memslot, id_node[1])
 		kvm_free_memslot(kvm, memslot);
-
-	kvfree(slots);
 }
 
 static umode_t kvm_stats_debugfs_mode(const struct _kvm_stats_desc *pdesc)
@@ -1044,8 +1036,9 @@ int __weak kvm_arch_create_vm_debugfs(struct kvm *kvm)
 static struct kvm *kvm_create_vm(unsigned long type)
 {
 	struct kvm *kvm = kvm_arch_alloc_vm();
+	struct kvm_memslots *slots;
 	int r = -ENOMEM;
-	int i;
+	int i, j;
 
 	if (!kvm)
 		return ERR_PTR(-ENOMEM);
@@ -1072,13 +1065,20 @@ static struct kvm *kvm_create_vm(unsigned long type)
 
 	refcount_set(&kvm->users_count, 1);
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
-		struct kvm_memslots *slots = kvm_alloc_memslots();
+		for (j = 0; j < 2; j++) {
+			slots = &kvm->__memslots[i][j];
 
-		if (!slots)
-			goto out_err_no_arch_destroy_vm;
-		/* Generations must be different for each address space. */
-		slots->generation = i;
-		rcu_assign_pointer(kvm->memslots[i], slots);
+			atomic_long_set(&slots->last_used_slot, (unsigned long)NULL);
+			slots->hva_tree = RB_ROOT_CACHED;
+			slots->gfn_tree = RB_ROOT;
+			hash_init(slots->id_hash);
+			slots->node_idx = j;
+
+			/* Generations must be different for each address space. */
+			slots->generation = i;
+		}
+
+		rcu_assign_pointer(kvm->memslots[i], &kvm->__memslots[i][0]);
 	}
 
 	for (i = 0; i < KVM_NR_BUSES; i++) {
@@ -1132,8 +1132,6 @@ static struct kvm *kvm_create_vm(unsigned long type)
 	WARN_ON_ONCE(!refcount_dec_and_test(&kvm->users_count));
 	for (i = 0; i < KVM_NR_BUSES; i++)
 		kfree(kvm_get_bus(kvm, i));
-	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++)
-		kvm_free_memslots(kvm, __kvm_memslots(kvm, i));
 	cleanup_srcu_struct(&kvm->irq_srcu);
 out_err_no_irq_srcu:
 	cleanup_srcu_struct(&kvm->srcu);
@@ -1198,8 +1196,10 @@ static void kvm_destroy_vm(struct kvm *kvm)
 #endif
 	kvm_arch_destroy_vm(kvm);
 	kvm_destroy_devices(kvm);
-	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++)
-		kvm_free_memslots(kvm, __kvm_memslots(kvm, i));
+	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
+		kvm_free_memslots(kvm, &kvm->__memslots[i][0]);
+		kvm_free_memslots(kvm, &kvm->__memslots[i][1]);
+	}
 	cleanup_srcu_struct(&kvm->irq_srcu);
 	cleanup_srcu_struct(&kvm->srcu);
 	kvm_arch_free_vm(kvm);
@@ -1269,231 +1269,136 @@ static int kvm_alloc_dirty_bitmap(struct kvm_memory_slot *memslot)
 	return 0;
 }
 
-static void kvm_replace_memslot(struct kvm_memslots *slots,
+static struct kvm_memslots *kvm_get_inactive_memslots(struct kvm *kvm, int as_id)
+{
+	struct kvm_memslots *active = __kvm_memslots(kvm, as_id);
+	int node_idx_inactive = active->node_idx ^ 1;
+
+	return &kvm->__memslots[as_id][node_idx_inactive];
+}
+
+/*
+ * Helper to get the address space ID when one of memslot pointers may be NULL.
+ * This also serves as a sanity that at least one of the pointers is non-NULL,
+ * and that their address space IDs don't diverge.
+ */
+static int kvm_memslots_get_as_id(struct kvm_memory_slot *a,
+				  struct kvm_memory_slot *b)
+{
+	if (WARN_ON_ONCE(!a && !b))
+		return 0;
+
+	if (!a)
+		return b->as_id;
+	if (!b)
+		return a->as_id;
+
+	WARN_ON_ONCE(a->as_id != b->as_id);
+	return a->as_id;
+}
+
+static void kvm_insert_gfn_node(struct kvm_memslots *slots,
+				struct kvm_memory_slot *slot)
+{
+	struct rb_root *gfn_tree = &slots->gfn_tree;
+	struct rb_node **node, *parent;
+	int idx = slots->node_idx;
+
+	parent = NULL;
+	for (node = &gfn_tree->rb_node; *node; ) {
+		struct kvm_memory_slot *tmp;
+
+		tmp = container_of(*node, struct kvm_memory_slot, gfn_node[idx]);
+		parent = *node;
+		if (slot->base_gfn < tmp->base_gfn)
+			node = &(*node)->rb_left;
+		else if (slot->base_gfn > tmp->base_gfn)
+			node = &(*node)->rb_right;
+		else
+			BUG();
+	}
+
+	rb_link_node(&slot->gfn_node[idx], parent, node);
+	rb_insert_color(&slot->gfn_node[idx], gfn_tree);
+}
+
+static void kvm_erase_gfn_node(struct kvm_memslots *slots,
+			       struct kvm_memory_slot *slot)
+{
+	rb_erase(&slot->gfn_node[slots->node_idx], &slots->gfn_tree);
+}
+
+static void kvm_replace_gfn_node(struct kvm_memslots *slots,
+				 struct kvm_memory_slot *old,
+				 struct kvm_memory_slot *new)
+{
+	int idx = slots->node_idx;
+
+	WARN_ON_ONCE(old->base_gfn != new->base_gfn);
+
+	rb_replace_node(&old->gfn_node[idx], &new->gfn_node[idx],
+			&slots->gfn_tree);
+}
+
+/*
+ * Replace @old with @new in the inactive memslots.
+ *
+ * With NULL @old this simply adds @new.
+ * With NULL @new this simply removes @old.
+ *
+ * If @new is non-NULL its hva_node[slots_idx] range has to be set
+ * appropriately.
+ */
+static void kvm_replace_memslot(struct kvm *kvm,
 				struct kvm_memory_slot *old,
 				struct kvm_memory_slot *new)
 {
-	/*
-	 * Remove the old memslot from the hash list and interval tree, copying
-	 * the node data would corrupt the structures.
-	 */
+	int as_id = kvm_memslots_get_as_id(old, new);
+	struct kvm_memslots *slots = kvm_get_inactive_memslots(kvm, as_id);
+	int idx = slots->node_idx;
+
 	if (old) {
-		hash_del(&old->id_node);
-		interval_tree_remove(&old->hva_node, &slots->hva_tree);
+		hash_del(&old->id_node[idx]);
+		interval_tree_remove(&old->hva_node[idx], &slots->hva_tree);
 
-		if (!new)
+		if ((long)old == atomic_long_read(&slots->last_used_slot))
+			atomic_long_set(&slots->last_used_slot, (long)new);
+
+		if (!new) {
+			kvm_erase_gfn_node(slots, old);
 			return;
+		}
 	}
 
 	/*
-	 * Copy the source *data*, not the pointer, to the destination.  If
-	 * @old is NULL, initialize @new's hva range.
+	 * Initialize @new's hva range.  Do this even when replacing an @old
+	 * slot, kvm_copy_memslot() deliberately does not touch node data.
 	 */
-	if (old) {
-		*new = *old;
-	} else if (new) {
-		new->hva_node.start = new->userspace_addr;
-		new->hva_node.last = new->userspace_addr +
-				     (new->npages << PAGE_SHIFT) - 1;
-	}
-
-	/* (Re)Add the new memslot. */
-	hash_add(slots->id_hash, &new->id_node, new->id);
-	interval_tree_insert(&new->hva_node, &slots->hva_tree);
-}
-
-static void kvm_shift_memslot(struct kvm_memslots *slots, int dst, int src)
-{
-	struct kvm_memory_slot *mslots = slots->memslots;
-
-	kvm_replace_memslot(slots, &mslots[src], &mslots[dst]);
-}
-
-/*
- * Delete a memslot by decrementing the number of used slots and shifting all
- * other entries in the array forward one spot.
- * @memslot is a detached dummy struct with just .id and .as_id filled.
- */
-static inline void kvm_memslot_delete(struct kvm_memslots *slots,
-				      struct kvm_memory_slot *memslot)
-{
-	struct kvm_memory_slot *mslots = slots->memslots;
-	struct kvm_memory_slot *oldslot = id_to_memslot(slots, memslot->id);
-	int i;
-
-	if (WARN_ON(!oldslot))
-		return;
-
-	slots->used_slots--;
-
-	if (atomic_read(&slots->last_used_slot) >= slots->used_slots)
-		atomic_set(&slots->last_used_slot, 0);
+	new->hva_node[idx].start = new->userspace_addr;
+	new->hva_node[idx].last = new->userspace_addr +
+				  (new->npages << PAGE_SHIFT) - 1;
 
 	/*
-	 * Remove the to-be-deleted memslot from the list/tree _before_ shifting
-	 * the trailing memslots forward, its data will be overwritten.
-	 * Defer the (somewhat pointless) copying of the memslot until after
-	 * the last slot has been shifted to avoid overwriting said last slot.
+	 * (Re)Add the new memslot.  There is no O(1) interval_tree_replace(),
+	 * hva_node needs to be swapped with remove+insert even though hva can't
+	 * change when replacing an existing slot.
 	 */
-	kvm_replace_memslot(slots, oldslot, NULL);
-
-	for (i = oldslot - mslots; i < slots->used_slots; i++)
-		kvm_shift_memslot(slots, i, i + 1);
-	mslots[i] = *memslot;
-}
-
-/*
- * "Insert" a new memslot by incrementing the number of used slots.  Returns
- * the new slot's initial index into the memslots array.
- */
-static inline int kvm_memslot_insert_back(struct kvm_memslots *slots)
-{
-	return slots->used_slots++;
-}
-
-/*
- * Move a changed memslot backwards in the array by shifting existing slots
- * with a higher GFN toward the front of the array.  Note, the changed memslot
- * itself is not preserved in the array, i.e. not swapped at this time, only
- * its new index into the array is tracked.  Returns the changed memslot's
- * current index into the memslots array.
- * The memslot at the returned index will not be in @slots->hva_tree or
- * @slots->id_hash by then.
- * @memslot is a detached struct with desired final data of the changed slot.
- */
-static inline int kvm_memslot_move_backward(struct kvm_memslots *slots,
-					    struct kvm_memory_slot *memslot)
-{
-	struct kvm_memory_slot *mslots = slots->memslots;
-	struct kvm_memory_slot *oldslot = id_to_memslot(slots, memslot->id);
-	int i;
-
-	if (!oldslot || !slots->used_slots)
-		return -1;
+	hash_add(slots->id_hash, &new->id_node[idx], new->id);
+	interval_tree_insert(&new->hva_node[idx], &slots->hva_tree);
 
 	/*
-	 * Delete the slot from the hash table and interval tree before sorting
-	 * the remaining slots, the slot's data may be overwritten when copying
-	 * slots as part of the sorting proccess.  update_memslots() will
-	 * unconditionally rewrite and re-add the entire slot.
+	 * If the memslot gfn is unchanged, rb_replace_node() can be used to
+	 * switch the node in the gfn tree instead of removing the old and
+	 * inserting the new as two separate operations. Replacement is a
+	 * single O(1) operation versus two O(log(n)) operations for
+	 * remove+insert.
 	 */
-	kvm_replace_memslot(slots, oldslot, NULL);
-
-	/*
-	 * Move the target memslot backward in the array by shifting existing
-	 * memslots with a higher GFN (than the target memslot) towards the
-	 * front of the array.
-	 */
-	for (i = oldslot - mslots; i < slots->used_slots - 1; i++) {
-		if (memslot->base_gfn > mslots[i + 1].base_gfn)
-			break;
-
-		WARN_ON_ONCE(memslot->base_gfn == mslots[i + 1].base_gfn);
-
-		kvm_shift_memslot(slots, i, i + 1);
-	}
-	return i;
-}
-
-/*
- * Move a changed memslot forwards in the array by shifting existing slots with
- * a lower GFN toward the back of the array.  Note, the changed memslot itself
- * is not preserved in the array, i.e. not swapped at this time, only its new
- * index into the array is tracked.  Returns the changed memslot's final index
- * into the memslots array.
- * The memslot at the returned index will not be in @slots->hva_tree or
- * @slots->id_hash by then.
- * @memslot is a detached struct with desired final data of the new or
- * changed slot.
- * Assumes that the memslot at @start index is not in @slots->hva_tree or
- * @slots->id_hash.
- */
-static inline int kvm_memslot_move_forward(struct kvm_memslots *slots,
-					   struct kvm_memory_slot *memslot,
-					   int start)
-{
-	struct kvm_memory_slot *mslots = slots->memslots;
-	int i;
-
-	for (i = start; i > 0; i--) {
-		if (memslot->base_gfn < mslots[i - 1].base_gfn)
-			break;
-
-		WARN_ON_ONCE(memslot->base_gfn == mslots[i - 1].base_gfn);
-
-		kvm_shift_memslot(slots, i, i - 1);
-	}
-	return i;
-}
-
-/*
- * Re-sort memslots based on their GFN to account for an added, deleted, or
- * moved memslot.  Sorting memslots by GFN allows using a binary search during
- * memslot lookup.
- *
- * IMPORTANT: Slots are sorted from highest GFN to lowest GFN!  I.e. the entry
- * at memslots[0] has the highest GFN.
- *
- * The sorting algorithm takes advantage of having initially sorted memslots
- * and knowing the position of the changed memslot.  Sorting is also optimized
- * by not swapping the updated memslot and instead only shifting other memslots
- * and tracking the new index for the update memslot.  Only once its final
- * index is known is the updated memslot copied into its position in the array.
- *
- *  - When deleting a memslot, the deleted memslot simply needs to be moved to
- *    the end of the array.
- *
- *  - When creating a memslot, the algorithm "inserts" the new memslot at the
- *    end of the array and then it forward to its correct location.
- *
- *  - When moving a memslot, the algorithm first moves the updated memslot
- *    backward to handle the scenario where the memslot's GFN was changed to a
- *    lower value.  update_memslots() then falls through and runs the same flow
- *    as creating a memslot to move the memslot forward to handle the scenario
- *    where its GFN was changed to a higher value.
- *
- * Note, slots are sorted from highest->lowest instead of lowest->highest for
- * historical reasons.  Originally, invalid memslots where denoted by having
- * GFN=0, thus sorting from highest->lowest naturally sorted invalid memslots
- * to the end of the array.  The current algorithm uses dedicated logic to
- * delete a memslot and thus does not rely on invalid memslots having GFN=0.
- *
- * The other historical motiviation for highest->lowest was to improve the
- * performance of memslot lookup.  KVM originally used a linear search starting
- * at memslots[0].  On x86, the largest memslot usually has one of the highest,
- * if not *the* highest, GFN, as the bulk of the guest's RAM is located in a
- * single memslot above the 4gb boundary.  As the largest memslot is also the
- * most likely to be referenced, sorting it to the front of the array was
- * advantageous.  The current binary search starts from the middle of the array
- * and uses an LRU pointer to improve performance for all memslots and GFNs.
- *
- * @memslot is a detached struct, not a part of the current or new memslot
- * array.
- */
-static void update_memslots(struct kvm_memslots *slots,
-			    struct kvm_memory_slot *memslot,
-			    enum kvm_mr_change change)
-{
-	int i;
-
-	if (change == KVM_MR_DELETE) {
-		kvm_memslot_delete(slots, memslot);
+	if (old && old->base_gfn == new->base_gfn) {
+		kvm_replace_gfn_node(slots, old, new);
 	} else {
-		if (change == KVM_MR_CREATE)
-			i = kvm_memslot_insert_back(slots);
-		else
-			i = kvm_memslot_move_backward(slots, memslot);
-		i = kvm_memslot_move_forward(slots, memslot, i);
-
-		if (WARN_ON_ONCE(i < 0))
-			return;
-
-		/*
-		 * Copy the memslot to its new position in memslots and update
-		 * its index accordingly.
-		 */
-		slots->memslots[i] = *memslot;
-		kvm_replace_memslot(slots, NULL, &slots->memslots[i]);
+		if (old)
+			kvm_erase_gfn_node(slots, old);
+		kvm_insert_gfn_node(slots, new);
 	}
 }
 
@@ -1511,11 +1416,12 @@ static int check_memory_region_flags(const struct kvm_userspace_memory_region *m
 	return 0;
 }
 
-static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
-		int as_id, struct kvm_memslots *slots)
+static void kvm_swap_active_memslots(struct kvm *kvm, int as_id)
 {
-	struct kvm_memslots *old_memslots = __kvm_memslots(kvm, as_id);
-	u64 gen = old_memslots->generation;
+	struct kvm_memslots *slots = kvm_get_inactive_memslots(kvm, as_id);
+
+	/* Grab the generation from the activate memslots. */
+	u64 gen = __kvm_memslots(kvm, as_id)->generation;
 
 	WARN_ON(gen & KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS);
 	slots->generation = gen | KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS;
@@ -1566,58 +1472,6 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
 	kvm_arch_memslots_updated(kvm, gen);
 
 	slots->generation = gen;
-
-	return old_memslots;
-}
-
-static size_t kvm_memslots_size(int slots)
-{
-	return sizeof(struct kvm_memslots) +
-	       (sizeof(struct kvm_memory_slot) * slots);
-}
-
-/*
- * Note, at a minimum, the current number of used slots must be allocated, even
- * when deleting a memslot, as we need a complete duplicate of the memslots for
- * use when invalidating a memslot prior to deleting/moving the memslot.
- */
-static struct kvm_memslots *kvm_dup_memslots(struct kvm_memslots *old,
-					     enum kvm_mr_change change)
-{
-	struct kvm_memslots *slots;
-	size_t new_size;
-	struct kvm_memory_slot *memslot;
-
-	if (change == KVM_MR_CREATE)
-		new_size = kvm_memslots_size(old->used_slots + 1);
-	else
-		new_size = kvm_memslots_size(old->used_slots);
-
-	slots = kvzalloc(new_size, GFP_KERNEL_ACCOUNT);
-	if (unlikely(!slots))
-		return NULL;
-
-	memcpy(slots, old, kvm_memslots_size(old->used_slots));
-
-	slots->hva_tree = RB_ROOT_CACHED;
-	hash_init(slots->id_hash);
-	kvm_for_each_memslot(memslot, slots) {
-		interval_tree_insert(&memslot->hva_node, &slots->hva_tree);
-		hash_add(slots->id_hash, &memslot->id_node, memslot->id);
-	}
-
-	return slots;
-}
-
-static void kvm_copy_memslots_arch(struct kvm_memslots *to,
-				   struct kvm_memslots *from)
-{
-	int i;
-
-	WARN_ON_ONCE(to->used_slots != from->used_slots);
-
-	for (i = 0; i < from->used_slots; i++)
-		to->memslots[i].arch = from->memslots[i].arch;
 }
 
 static int kvm_prepare_memory_region(struct kvm *kvm,
@@ -1672,31 +1526,214 @@ static void kvm_commit_memory_region(struct kvm *kvm,
 
 	kvm_arch_commit_memory_region(kvm, old, new, change);
 
-	/*
-	 * Free the old memslot's metadata.  On DELETE, free the whole thing,
-	 * otherwise free the dirty bitmap as needed (the below effectively
-	 * checks both the flags and whether a ring buffer is being used).
-	 */
-	if (change == KVM_MR_DELETE)
+	switch (change) {
+	case KVM_MR_CREATE:
+		/* Nothing more to do. */
+		break;
+	case KVM_MR_DELETE:
+		/* Free the old memslot and all its metadata. */
 		kvm_free_memslot(kvm, old);
-	else if (old->dirty_bitmap && !new->dirty_bitmap)
-		kvm_destroy_dirty_bitmap(old);
+		break;
+	case KVM_MR_MOVE:
+	case KVM_MR_FLAGS_ONLY:
+		/*
+		 * Free the dirty bitmap as needed; the below check encompasses
+		 * both the flags and whether a ring buffer is being used)
+		 */
+		if (old->dirty_bitmap && !new->dirty_bitmap)
+			kvm_destroy_dirty_bitmap(old);
+
+		/*
+		 * The final quirk.  Free the detached, old slot, but only its
+		 * memory, not any metadata.  Metadata, including arch specific
+		 * data, may be reused by @new.
+		 */
+		kfree(old);
+		break;
+	default:
+		BUG();
+	}
+}
+
+/*
+ * Activate @new, which must be installed in the inactive slots by the caller,
+ * by swapping the active slots and then propagating @new to @old once @old is
+ * unreachable and can be safely modified.
+ *
+ * With NULL @old this simply adds @new to @active (while swapping the sets).
+ * With NULL @new this simply removes @old from @active and frees it
+ * (while also swapping the sets).
+ */
+static void kvm_activate_memslot(struct kvm *kvm,
+				 struct kvm_memory_slot *old,
+				 struct kvm_memory_slot *new)
+{
+	int as_id = kvm_memslots_get_as_id(old, new);
+
+	kvm_swap_active_memslots(kvm, as_id);
+
+	/* Propagate the new memslot to the now inactive memslots. */
+	kvm_replace_memslot(kvm, old, new);
+}
+
+static void kvm_copy_memslot(struct kvm_memory_slot *dest,
+			     const struct kvm_memory_slot *src)
+{
+	dest->base_gfn = src->base_gfn;
+	dest->npages = src->npages;
+	dest->dirty_bitmap = src->dirty_bitmap;
+	dest->arch = src->arch;
+	dest->userspace_addr = src->userspace_addr;
+	dest->flags = src->flags;
+	dest->id = src->id;
+	dest->as_id = src->as_id;
+}
+
+static void kvm_invalidate_memslot(struct kvm *kvm,
+				   struct kvm_memory_slot *old,
+				   struct kvm_memory_slot *working_slot)
+{
+	/*
+	 * Mark the current slot INVALID.  As with all memslot modifications,
+	 * this must be done on an unreachable slot to avoid modifying the
+	 * current slot in the active tree.
+	 */
+	kvm_copy_memslot(working_slot, old);
+	working_slot->flags |= KVM_MEMSLOT_INVALID;
+	kvm_replace_memslot(kvm, old, working_slot);
+
+	/*
+	 * Activate the slot that is now marked INVALID, but don't propagate
+	 * the slot to the now inactive slots. The slot is either going to be
+	 * deleted or recreated as a new slot.
+	 */
+	kvm_swap_active_memslots(kvm, old->as_id);
+
+	/*
+	 * From this point no new shadow pages pointing to a deleted, or moved,
+	 * memslot will be created.  Validation of sp->gfn happens in:
+	 *	- gfn_to_hva (kvm_read_guest, gfn_to_pfn)
+	 *	- kvm_is_visible_gfn (mmu_check_root)
+	 */
+	kvm_arch_flush_shadow_memslot(kvm, old);
+
+	/* Was released by kvm_swap_active_memslots, reacquire. */
+	mutex_lock(&kvm->slots_arch_lock);
+
+	/*
+	 * Copy the arch-specific field of the newly-installed slot back to the
+	 * old slot as the arch data could have changed between releasing
+	 * slots_arch_lock in install_new_memslots() and re-acquiring the lock
+	 * above.  Writers are required to retrieve memslots *after* acquiring
+	 * slots_arch_lock, thus the active slot's data is guaranteed to be fresh.
+	 */
+	old->arch = working_slot->arch;
+}
+
+static void kvm_create_memslot(struct kvm *kvm,
+			       const struct kvm_memory_slot *new,
+			       struct kvm_memory_slot *working)
+{
+	/*
+	 * Add the new memslot to the inactive set as a copy of the
+	 * new memslot data provided by userspace.
+	 */
+	kvm_copy_memslot(working, new);
+	kvm_replace_memslot(kvm, NULL, working);
+	kvm_activate_memslot(kvm, NULL, working);
+}
+
+static void kvm_delete_memslot(struct kvm *kvm,
+			       struct kvm_memory_slot *old,
+			       struct kvm_memory_slot *invalid_slot)
+{
+	/*
+	 * Remove the old memslot (in the inactive memslots) by passing NULL as
+	 * the "new" slot.
+	 */
+	kvm_replace_memslot(kvm, old, NULL);
+
+	/* And do the same for the invalid version in the active slot. */
+	kvm_activate_memslot(kvm, invalid_slot, NULL);
+
+	/* Free the invalid slot, the caller will clean up the old slot. */
+	kfree(invalid_slot);
+}
+
+static struct kvm_memory_slot *kvm_move_memslot(struct kvm *kvm,
+						struct kvm_memory_slot *old,
+						const struct kvm_memory_slot *new,
+						struct kvm_memory_slot *invalid_slot)
+{
+	struct kvm_memslots *slots = kvm_get_inactive_memslots(kvm, old->as_id);
+
+	/*
+	 * The memslot's gfn is changing, remove it from the inactive tree, it
+	 * will be re-added with its updated gfn. Because its range is
+	 * changing, an in-place replace is not possible.
+	 */
+	kvm_erase_gfn_node(slots, old);
+
+	/*
+	 * The old slot is now fully disconnected, reuse its memory for the
+	 * persistent copy of "new".
+	 */
+	kvm_copy_memslot(old, new);
+
+	/* Re-add to the gfn tree with the updated gfn */
+	kvm_insert_gfn_node(slots, old);
+
+	/* Replace the current INVALID slot with the updated memslot. */
+	kvm_activate_memslot(kvm, invalid_slot, old);
+
+	/*
+	 * Clear the INVALID flag so that the invalid_slot is now a perfect
+	 * copy of the old slot.  Return it for cleanup in the caller.
+	 */
+	WARN_ON_ONCE(!(invalid_slot->flags & KVM_MEMSLOT_INVALID));
+	invalid_slot->flags &= ~KVM_MEMSLOT_INVALID;
+	return invalid_slot;
+}
+
+static void kvm_update_flags_memslot(struct kvm *kvm,
+				     struct kvm_memory_slot *old,
+				     const struct kvm_memory_slot *new,
+				     struct kvm_memory_slot *working_slot)
+{
+	/*
+	 * Similar to the MOVE case, but the slot doesn't need to be zapped as
+	 * an intermediate step. Instead, the old memslot is simply replaced
+	 * with a new, updated copy in both memslot sets.
+	 */
+	kvm_copy_memslot(working_slot, new);
+	kvm_replace_memslot(kvm, old, working_slot);
+	kvm_activate_memslot(kvm, old, working_slot);
 }
 
 static int kvm_set_memslot(struct kvm *kvm,
+			   struct kvm_memory_slot *old,
 			   struct kvm_memory_slot *new,
 			   enum kvm_mr_change change)
 {
-	struct kvm_memory_slot *slot, old;
-	struct kvm_memslots *slots;
+	struct kvm_memory_slot *working;
 	int r;
 
 	/*
-	 * Released in install_new_memslots.
+	 * Modifications are done on an unreachable slot.  Any changes are then
+	 * (eventually) propagated to both the active and inactive slots.  This
+	 * allocation would ideally be on-demand (in helpers), but is done here
+	 * to avoid having to handle failure after kvm_prepare_memory_region().
+	 */
+	working = kzalloc(sizeof(*working), GFP_KERNEL_ACCOUNT);
+	if (!working)
+		return -ENOMEM;
+
+	/*
+	 * Released in kvm_swap_active_memslots.
 	 *
 	 * Must be held from before the current memslots are copied until
 	 * after the new memslots are installed with rcu_assign_pointer,
-	 * then released before the synchronize srcu in install_new_memslots.
+	 * then released before the synchronize srcu in kvm_swap_active_memslots.
 	 *
 	 * When modifying memslots outside of the slots_lock, must be held
 	 * before reading the pointer to the current memslots until after all
@@ -1707,87 +1744,60 @@ static int kvm_set_memslot(struct kvm *kvm,
 	 */
 	mutex_lock(&kvm->slots_arch_lock);
 
-	slots = kvm_dup_memslots(__kvm_memslots(kvm, new->as_id), change);
-	if (!slots) {
-		mutex_unlock(&kvm->slots_arch_lock);
-		return -ENOMEM;
-	}
-
-	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) {
-		/*
-		 * Note, the INVALID flag needs to be in the appropriate entry
-		 * in the freshly allocated memslots, not in @old or @new.
-		 */
-		slot = id_to_memslot(slots, new->id);
-		slot->flags |= KVM_MEMSLOT_INVALID;
-
-		/*
-		 * We can re-use the old memslots, the only difference from the
-		 * newly installed memslots is the invalid flag, which will get
-		 * dropped by update_memslots anyway.  We'll also revert to the
-		 * old memslots if preparing the new memory region fails.
-		 */
-		slots = install_new_memslots(kvm, new->as_id, slots);
-
-		/* From this point no new shadow pages pointing to a deleted,
-		 * or moved, memslot will be created.
-		 *
-		 * validation of sp->gfn happens in:
-		 *	- gfn_to_hva (kvm_read_guest, gfn_to_pfn)
-		 *	- kvm_is_visible_gfn (mmu_check_root)
-		 */
-		kvm_arch_flush_shadow_memslot(kvm, slot);
-
-		/* Released in install_new_memslots. */
-		mutex_lock(&kvm->slots_arch_lock);
-
-		/*
-		 * The arch-specific fields of the now-active memslots could
-		 * have been modified between releasing slots_arch_lock in
-		 * install_new_memslots and re-acquiring slots_arch_lock above.
-		 * Copy them to the inactive memslots.  Arch code is required
-		 * to retrieve memslots *after* acquiring slots_arch_lock, thus
-		 * the active memslots are guaranteed to be fresh.
-		 */
-		kvm_copy_memslots_arch(slots, __kvm_memslots(kvm, new->as_id));
-	}
-
 	/*
-	 * Make a full copy of the old memslot, the pointer will become stale
-	 * when the memslots are re-sorted by update_memslots(), and the old
-	 * memslot needs to be referenced after calling update_memslots(), e.g.
-	 * to free its resources and for arch specific behavior.  This needs to
-	 * happen *after* (re)acquiring slots_arch_lock.
+	 * Invalidate the old slot if it's being deleted or moved.  This is
+	 * done prior to actually deleting/moving the memslot to allow vCPUs to
+	 * continue running by ensuring there are no mappings or shadow pages
+	 * for the memslot when it is deleted/moved.  Without pre-invalidation
+	 * (and without a lock), a window would exist between effecting the
+	 * delete/move and committing the changes in arch code where KVM or a
+	 * guest could access a non-existent memslot.
 	 */
-	slot = id_to_memslot(slots, new->id);
-	if (slot) {
-		old = *slot;
-	} else {
-		WARN_ON_ONCE(change != KVM_MR_CREATE);
-		memset(&old, 0, sizeof(old));
-		old.id = new->id;
-		old.as_id = new->as_id;
-	}
-
-	r = kvm_prepare_memory_region(kvm, &old, new, change);
-	if (r)
-		goto out_slots;
-
-	update_memslots(slots, new, change);
-	slots = install_new_memslots(kvm, new->as_id, slots);
-
-	kvm_commit_memory_region(kvm, &old, new, change);
-
-	kvfree(slots);
-	return 0;
-
-out_slots:
 	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE)
-		slots = install_new_memslots(kvm, new->as_id, slots);
+		kvm_invalidate_memslot(kvm, old, working);
+
+	r = kvm_prepare_memory_region(kvm, old, new, change);
+	if (r) {
+		/*
+		 * For DELETE/MOVE, revert the above INVALID change.  No
+		 * modifications required since the original slot was preserved
+		 * in the inactive slots.  Changing the active memslots also
+		 * release slots_arch_lock.
+		 */
+		if (change == KVM_MR_DELETE || change == KVM_MR_MOVE)
+			kvm_activate_memslot(kvm, working, old);
+		else
+			mutex_unlock(&kvm->slots_arch_lock);
+		kfree(working);
+		return r;
+	}
+
+	/*
+	 * For DELETE and MOVE, the working slot is now active as the INVALID
+	 * version of the old slot.  MOVE is particularly special as it reuses
+	 * the old slot and returns a copy of the old slot (in working_slot).
+	 * For CREATE, there is no old slot.  For DELETE and FLAGS_ONLY, the
+	 * old slot is detached but otherwise preserved.
+	 */
+	if (change == KVM_MR_CREATE)
+		kvm_create_memslot(kvm, new, working);
+	else if (change == KVM_MR_DELETE)
+		kvm_delete_memslot(kvm, old, working);
+	else if (change == KVM_MR_MOVE)
+		old = kvm_move_memslot(kvm, old, new, working);
+	else if (change == KVM_MR_FLAGS_ONLY)
+		kvm_update_flags_memslot(kvm, old, new, working);
 	else
-		mutex_unlock(&kvm->slots_arch_lock);
-	kvfree(slots);
-	return r;
+		BUG();
+
+	/*
+	 * No need to refresh new->arch, changes after dropping slots_arch_lock
+	 * will directly hit the final, active memsot.  Architectures are
+	 * responsible for knowing that new->arch may be stale.
+	 */
+	kvm_commit_memory_region(kvm, old, new, change);
+
+	return 0;
 }
 
 /*
@@ -1848,7 +1858,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		new.id = id;
 		new.as_id = as_id;
 
-		return kvm_set_memslot(kvm, &new, KVM_MR_DELETE);
+		return kvm_set_memslot(kvm, old, &new, KVM_MR_DELETE);
 	}
 
 	new.as_id = as_id;
@@ -1885,8 +1895,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	}
 
 	if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
+		int bkt;
+
 		/* Check for overlaps */
-		kvm_for_each_memslot(tmp, __kvm_memslots(kvm, as_id)) {
+		kvm_for_each_memslot(tmp, bkt, __kvm_memslots(kvm, as_id)) {
 			if (tmp->id == id)
 				continue;
 			if (!((new.base_gfn + new.npages <= tmp->base_gfn) ||
@@ -1895,7 +1907,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		}
 	}
 
-	return kvm_set_memslot(kvm, &new, change);
+	return kvm_set_memslot(kvm, old, &new, change);
 }
 EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
 
@@ -2200,21 +2212,30 @@ EXPORT_SYMBOL_GPL(gfn_to_memslot);
 struct kvm_memory_slot *kvm_vcpu_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn)
 {
 	struct kvm_memslots *slots = kvm_vcpu_memslots(vcpu);
+	u64 gen = slots->generation;
 	struct kvm_memory_slot *slot;
-	int slot_index;
 
-	slot = try_get_memslot(slots, vcpu->last_used_slot, gfn);
+	/*
+	 * This also protects against using a memslot from a different address space,
+	 * since different address spaces have different generation numbers.
+	 */
+	if (unlikely(gen != vcpu->last_used_slot_gen)) {
+		vcpu->last_used_slot = NULL;
+		vcpu->last_used_slot_gen = gen;
+	}
+
+	slot = try_get_memslot(vcpu->last_used_slot, gfn);
 	if (slot)
 		return slot;
 
 	/*
 	 * Fall back to searching all memslots. We purposely use
 	 * search_memslots() instead of __gfn_to_memslot() to avoid
-	 * thrashing the VM-wide last_used_index in kvm_memslots.
+	 * thrashing the VM-wide last_used_slot in kvm_memslots.
 	 */
-	slot = search_memslots(slots, gfn, &slot_index, false);
+	slot = search_memslots(slots, gfn, false);
 	if (slot) {
-		vcpu->last_used_slot = slot_index;
+		vcpu->last_used_slot = slot;
 		return slot;
 	}
 
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 26/30] KVM: Keep memslots in tree-based structures instead of array-based ones

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> 
> The current memslot code uses a (reverse gfn-ordered) memslot array for
> keeping track of them.
> 
> Because the memslot array that is currently in use cannot be modified
> every memslot management operation (create, delete, move, change flags)
> has to make a copy of the whole array so it has a scratch copy to work on.
> 
> Strictly speaking, however, it is only necessary to make copy of the
> memslot that is being modified, copying all the memslots currently present
> is just a limitation of the array-based memslot implementation.
> 
> Two memslot sets, however, are still needed so the VM continues to run
> on the currently active set while the requested operation is being
> performed on the second, currently inactive one.
> 
> In order to have two memslot sets, but only one copy of actual memslots
> it is necessary to split out the memslot data from the memslot sets.
> 
> The memslots themselves should be also kept independent of each other
> so they can be individually added or deleted.
> 
> These two memslot sets should normally point to the same set of
> memslots. They can, however, be desynchronized when performing a
> memslot management operation by replacing the memslot to be modified
> by its copy.  After the operation is complete, both memslot sets once
> again point to the same, common set of memslot data.
> 
> This commit implements the aforementioned idea.
> 
> For tracking of gfns an ordinary rbtree is used since memslots cannot
> overlap in the guest address space and so this data structure is
> sufficient for ensuring that lookups are done quickly.
> 
> The "last used slot" mini-caches (both per-slot set one and per-vCPU one),
> that keep track of the last found-by-gfn memslot, are still present in the
> new code.
> 
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> Co-developed-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   arch/arm64/kvm/mmu.c                |   8 +-
>   arch/powerpc/kvm/book3s_64_mmu_hv.c |   4 +-
>   arch/powerpc/kvm/book3s_hv.c        |   3 +-
>   arch/powerpc/kvm/book3s_hv_nested.c |   4 +-
>   arch/powerpc/kvm/book3s_hv_uvmem.c  |  14 +-
>   arch/s390/kvm/kvm-s390.c            |  24 +-
>   arch/s390/kvm/kvm-s390.h            |   6 +-
>   arch/x86/kvm/debugfs.c              |   6 +-
>   arch/x86/kvm/mmu/mmu.c              |   8 +-
>   include/linux/kvm_host.h            | 141 +++--
>   virt/kvm/kvm_main.c                 | 809 ++++++++++++++--------------
>   11 files changed, 524 insertions(+), 503 deletions(-)
> 
(..)
> +/*
> + * Replace @old with @new in the inactive memslots.
> + *
> + * With NULL @old this simply adds @new.
> + * With NULL @new this simply removes @old.
> + *
> + * If @new is non-NULL its hva_node[slots_idx] range has to be set
> + * appropriately.
> + */
> +static void kvm_replace_memslot(struct kvm *kvm,
>   				struct kvm_memory_slot *old,
>   				struct kvm_memory_slot *new)
>   {
> -	/*
> -	 * Remove the old memslot from the hash list and interval tree, copying
> -	 * the node data would corrupt the structures.
> -	 */
> +	int as_id = kvm_memslots_get_as_id(old, new);
> +	struct kvm_memslots *slots = kvm_get_inactive_memslots(kvm, as_id);
> +	int idx = slots->node_idx;
> +
>   	if (old) {
> -		hash_del(&old->id_node);
> -		interval_tree_remove(&old->hva_node, &slots->hva_tree);
> +		hash_del(&old->id_node[idx]);
> +		interval_tree_remove(&old->hva_node[idx], &slots->hva_tree);
>   
> -		if (!new)
> +		if ((long)old == atomic_long_read(&slots->last_used_slot))
> +			atomic_long_set(&slots->last_used_slot, (long)new);

Open-coding cmpxchg() is way less readable than a direct call.

The open-coded version also compiles on x86 to multiple instructions with
a branch, instead of just a single instruction.

> +static void kvm_invalidate_memslot(struct kvm *kvm,
> +				   struct kvm_memory_slot *old,
> +				   struct kvm_memory_slot *working_slot)
> +{
> +	/*
> +	 * Mark the current slot INVALID.  As with all memslot modifications,
> +	 * this must be done on an unreachable slot to avoid modifying the
> +	 * current slot in the active tree.
> +	 */
> +	kvm_copy_memslot(working_slot, old);
> +	working_slot->flags |= KVM_MEMSLOT_INVALID;
> +	kvm_replace_memslot(kvm, old, working_slot);
> +
> +	/*
> +	 * Activate the slot that is now marked INVALID, but don't propagate
> +	 * the slot to the now inactive slots. The slot is either going to be
> +	 * deleted or recreated as a new slot.
> +	 */
> +	kvm_swap_active_memslots(kvm, old->as_id);
> +
> +	/*
> +	 * From this point no new shadow pages pointing to a deleted, or moved,
> +	 * memslot will be created.  Validation of sp->gfn happens in:
> +	 *	- gfn_to_hva (kvm_read_guest, gfn_to_pfn)
> +	 *	- kvm_is_visible_gfn (mmu_check_root)
> +	 */
> +	kvm_arch_flush_shadow_memslot(kvm, old);

This should flush the currently active slot (that is, "working_slot",
not "old") to not introduce a behavior change with respect to the existing
code.

That's also what the previous version of this patch set did.

Thanks,
Maciej

Re: [PATCH v5.5 26/30] KVM: Keep memslots in tree-based structures instead of array-based ones

[Sean Christopherson]

On Fri, Nov 12, 2021, Maciej S. Szmigiero wrote:
> On 04.11.2021 01:25, Sean Christopherson wrote:
> > -	/*
> > -	 * Remove the old memslot from the hash list and interval tree, copying
> > -	 * the node data would corrupt the structures.
> > -	 */
> > +	int as_id = kvm_memslots_get_as_id(old, new);
> > +	struct kvm_memslots *slots = kvm_get_inactive_memslots(kvm, as_id);
> > +	int idx = slots->node_idx;
> > +
> >   	if (old) {
> > -		hash_del(&old->id_node);
> > -		interval_tree_remove(&old->hva_node, &slots->hva_tree);
> > +		hash_del(&old->id_node[idx]);
> > +		interval_tree_remove(&old->hva_node[idx], &slots->hva_tree);
> > -		if (!new)
> > +		if ((long)old == atomic_long_read(&slots->last_used_slot))
> > +			atomic_long_set(&slots->last_used_slot, (long)new);
> 
> Open-coding cmpxchg() is way less readable than a direct call.

Doh, I meant to call this out and/or add a comment.

My objection to cmpxchg() is that it implies atomicity is required (the kernel's
version adds the lock), which is very much not the case.  So this isn't strictly
an open-coded version of cmpxchg().

> The open-coded version also compiles on x86 to multiple instructions with
> a branch, instead of just a single instruction.

Yeah.  The lock can't be contended, so that part of cmpxchg is a non-issue.  But
that's also why I don't love using cmpxchg.

I don't have a strong preference, I just got briefly confused by the atomicity part.

> > +static void kvm_invalidate_memslot(struct kvm *kvm,
> > +				   struct kvm_memory_slot *old,
> > +				   struct kvm_memory_slot *working_slot)
> > +{
> > +	/*
> > +	 * Mark the current slot INVALID.  As with all memslot modifications,
> > +	 * this must be done on an unreachable slot to avoid modifying the
> > +	 * current slot in the active tree.
> > +	 */
> > +	kvm_copy_memslot(working_slot, old);
> > +	working_slot->flags |= KVM_MEMSLOT_INVALID;
> > +	kvm_replace_memslot(kvm, old, working_slot);
> > +
> > +	/*
> > +	 * Activate the slot that is now marked INVALID, but don't propagate
> > +	 * the slot to the now inactive slots. The slot is either going to be
> > +	 * deleted or recreated as a new slot.
> > +	 */
> > +	kvm_swap_active_memslots(kvm, old->as_id);
> > +
> > +	/*
> > +	 * From this point no new shadow pages pointing to a deleted, or moved,
> > +	 * memslot will be created.  Validation of sp->gfn happens in:
> > +	 *	- gfn_to_hva (kvm_read_guest, gfn_to_pfn)
> > +	 *	- kvm_is_visible_gfn (mmu_check_root)
> > +	 */
> > +	kvm_arch_flush_shadow_memslot(kvm, old);
> 
> This should flush the currently active slot (that is, "working_slot",
> not "old") to not introduce a behavior change with respect to the existing
> code.
> 
> That's also what the previous version of this patch set did.

Eww.  I would much prefer to "fix" the existing code in a prep patch.  It shouldn't
matter, but arch code really should not get passed an INVALID slot.

Re: [PATCH v5.5 26/30] KVM: Keep memslots in tree-based structures instead of array-based ones

[Maciej S. Szmigiero]

On 12.11.2021 01:51, Sean Christopherson wrote:
> On Fri, Nov 12, 2021, Maciej S. Szmigiero wrote:
>> On 04.11.2021 01:25, Sean Christopherson wrote:
>>> -	/*
>>> -	 * Remove the old memslot from the hash list and interval tree, copying
>>> -	 * the node data would corrupt the structures.
>>> -	 */
>>> +	int as_id = kvm_memslots_get_as_id(old, new);
>>> +	struct kvm_memslots *slots = kvm_get_inactive_memslots(kvm, as_id);
>>> +	int idx = slots->node_idx;
>>> +
>>>    	if (old) {
>>> -		hash_del(&old->id_node);
>>> -		interval_tree_remove(&old->hva_node, &slots->hva_tree);
>>> +		hash_del(&old->id_node[idx]);
>>> +		interval_tree_remove(&old->hva_node[idx], &slots->hva_tree);
>>> -		if (!new)
>>> +		if ((long)old == atomic_long_read(&slots->last_used_slot))
>>> +			atomic_long_set(&slots->last_used_slot, (long)new);
>>
>> Open-coding cmpxchg() is way less readable than a direct call.
> 
> Doh, I meant to call this out and/or add a comment.
> 
> My objection to cmpxchg() is that it implies atomicity is required (the kernel's
> version adds the lock), which is very much not the case.  So this isn't strictly
> an open-coded version of cmpxchg().
> 
>> The open-coded version also compiles on x86 to multiple instructions with
>> a branch, instead of just a single instruction.
> 
> Yeah.  The lock can't be contended, so that part of cmpxchg is a non-issue.  But
> that's also why I don't love using cmpxchg.
> 
> I don't have a strong preference, I just got briefly confused by the atomicity part.

We can simply add a comment there to explain that the atomicity isn't actually
strictly required here - will do that.

>>> +static void kvm_invalidate_memslot(struct kvm *kvm,
>>> +				   struct kvm_memory_slot *old,
>>> +				   struct kvm_memory_slot *working_slot)
>>> +{
>>> +	/*
>>> +	 * Mark the current slot INVALID.  As with all memslot modifications,
>>> +	 * this must be done on an unreachable slot to avoid modifying the
>>> +	 * current slot in the active tree.
>>> +	 */
>>> +	kvm_copy_memslot(working_slot, old);
>>> +	working_slot->flags |= KVM_MEMSLOT_INVALID;
>>> +	kvm_replace_memslot(kvm, old, working_slot);
>>> +
>>> +	/*
>>> +	 * Activate the slot that is now marked INVALID, but don't propagate
>>> +	 * the slot to the now inactive slots. The slot is either going to be
>>> +	 * deleted or recreated as a new slot.
>>> +	 */
>>> +	kvm_swap_active_memslots(kvm, old->as_id);
>>> +
>>> +	/*
>>> +	 * From this point no new shadow pages pointing to a deleted, or moved,
>>> +	 * memslot will be created.  Validation of sp->gfn happens in:
>>> +	 *	- gfn_to_hva (kvm_read_guest, gfn_to_pfn)
>>> +	 *	- kvm_is_visible_gfn (mmu_check_root)
>>> +	 */
>>> +	kvm_arch_flush_shadow_memslot(kvm, old);
>>
>> This should flush the currently active slot (that is, "working_slot",
>> not "old") to not introduce a behavior change with respect to the existing
>> code.
>>
>> That's also what the previous version of this patch set did.
> 
> Eww.  I would much prefer to "fix" the existing code in a prep patch.  It shouldn't
> matter, but arch code really should not get passed an INVALID slot.
> 

I will add a separate patch that switches that kvm_arch_flush_shadow_memslot()
call to use a valid (old) memslot instead.

It is actually simpler to do it *after* the main patch series to not add
more dead code that next patches remove anyway.

Thanks,
Maciej

[PATCH v5.5 27/30] KVM: Optimize gfn lookup in kvm_zap_gfn_range()

[Sean Christopherson]

From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

Introduce a memslots gfn upper bound operation and use it to optimize
kvm_zap_gfn_range().
This way this handler can do a quick lookup for intersecting gfns and won't
have to do a linear scan of the whole memslot set.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Not-signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/mmu/mmu.c   | 11 +++++--
 include/linux/kvm_host.h | 69 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 78 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 09ff0ccaa203..14e41278c069 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5714,16 +5714,20 @@ static bool __kvm_zap_rmaps(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
 {
 	const struct kvm_memory_slot *memslot;
 	struct kvm_memslots *slots;
+	struct rb_node *node;
 	bool flush = false;
 	gfn_t start, end;
-	int i, bkt;
+	int i, idx;
 
 	if (!kvm_memslots_have_rmaps(kvm))
 		return flush;
 
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
 		slots = __kvm_memslots(kvm, i);
-		kvm_for_each_memslot(memslot, bkt, slots) {
+		idx = slots->node_idx;
+
+		kvm_for_each_memslot_in_gfn_range(node, slots, gfn_start, gfn_end) {
+			memslot = container_of(node, struct kvm_memory_slot, gfn_node[idx]);
 			start = max(gfn_start, memslot->base_gfn);
 			end = min(gfn_end, memslot->base_gfn + memslot->npages);
 			if (start >= end)
@@ -5747,6 +5751,9 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
 	bool flush;
 	int i;
 
+	if (WARN_ON_ONCE(gfn_end <= gfn_start))
+		return;
+
 	write_lock(&kvm->mmu_lock);
 
 	kvm_inc_notifier_count(kvm, gfn_start, gfn_end);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 6888f3c2e04b..810a5b958697 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -832,6 +832,75 @@ struct kvm_memory_slot *id_to_memslot(struct kvm_memslots *slots, int id)
 	return NULL;
 }
 
+static inline
+struct rb_node *kvm_memslots_gfn_upper_bound(struct kvm_memslots *slots, gfn_t gfn)
+{
+	int idx = slots->node_idx;
+	struct rb_node *node, *result = NULL;
+
+	for (node = slots->gfn_tree.rb_node; node; ) {
+		struct kvm_memory_slot *slot;
+
+		slot = container_of(node, struct kvm_memory_slot, gfn_node[idx]);
+		if (gfn < slot->base_gfn) {
+			result = node;
+			node = node->rb_left;
+		} else
+			node = node->rb_right;
+	}
+
+	return result;
+}
+
+static inline
+struct rb_node *kvm_for_each_in_gfn_first(struct kvm_memslots *slots, gfn_t start)
+{
+	struct rb_node *node;
+
+	/*
+	 * Find the slot with the lowest gfn that can possibly intersect with
+	 * the range, so we'll ideally have slot start <= range start
+	 */
+	node = kvm_memslots_gfn_upper_bound(slots, start);
+	if (node) {
+		struct rb_node *pnode;
+
+		/*
+		 * A NULL previous node means that the very first slot
+		 * already has a higher start gfn.
+		 * In this case slot start > range start.
+		 */
+		pnode = rb_prev(node);
+		if (pnode)
+			node = pnode;
+	} else {
+		/* a NULL node below means no slots */
+		node = rb_last(&slots->gfn_tree);
+	}
+
+	return node;
+}
+
+static inline
+bool kvm_for_each_in_gfn_no_more(struct kvm_memslots *slots, struct rb_node *node, gfn_t end)
+{
+	struct kvm_memory_slot *memslot;
+
+	memslot = container_of(node, struct kvm_memory_slot, gfn_node[slots->node_idx]);
+
+	/*
+	 * If this slot starts beyond or at the end of the range so does
+	 * every next one
+	 */
+	return memslot->base_gfn >= end;
+}
+
+/* Iterate over each memslot *possibly* intersecting [start, end) range */
+#define kvm_for_each_memslot_in_gfn_range(node, slots, start, end)	\
+	for (node = kvm_for_each_in_gfn_first(slots, start);		\
+	     node && !kvm_for_each_in_gfn_no_more(slots, node, end);	\
+	     node = rb_next(node))					\
+
 /*
  * KVM_SET_USER_MEMORY_REGION ioctl allows the following operations:
  * - create a new memory slot
-- 
2.33.1.1089.g2158813163f-goog

[PATCH v5.5 28/30] KVM: Optimize overlapping memslots check

[Sean Christopherson]

From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

Do a quick lookup for possibly overlapping gfns when creating or moving
a memslot instead of performing a linear scan of the whole memslot set.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
[sean: tweaked params to avoid churn in future cleanup]
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 virt/kvm/kvm_main.c | 46 +++++++++++++++++++++++++++++++--------------
 1 file changed, 32 insertions(+), 14 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d095e01838bf..d22e40225703 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1800,6 +1800,29 @@ static int kvm_set_memslot(struct kvm *kvm,
 	return 0;
 }
 
+static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
+				      gfn_t start, gfn_t end)
+{
+	int idx = slots->node_idx;
+	struct rb_node *node;
+
+	kvm_for_each_memslot_in_gfn_range(node, slots, start, end) {
+		struct kvm_memory_slot *cslot;
+		gfn_t cend;
+
+		cslot = container_of(node, struct kvm_memory_slot, gfn_node[idx]);
+		cend = cslot->base_gfn + cslot->npages;
+		if (cslot->id == id)
+			continue;
+
+		/* kvm_for_each_in_gfn_no_more() guarantees that cslot->base_gfn < nend */
+		if (cend > start)
+			return true;
+	}
+
+	return false;
+}
+
 /*
  * Allocate some memory and give it an address in the guest physical address
  * space.
@@ -1811,8 +1834,9 @@ static int kvm_set_memslot(struct kvm *kvm,
 int __kvm_set_memory_region(struct kvm *kvm,
 			    const struct kvm_userspace_memory_region *mem)
 {
-	struct kvm_memory_slot *old, *tmp;
+	struct kvm_memory_slot *old;
 	struct kvm_memory_slot new;
+	struct kvm_memslots *slots;
 	enum kvm_mr_change change;
 	int as_id, id;
 	int r;
@@ -1841,11 +1865,13 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
 		return -EINVAL;
 
+	slots = __kvm_memslots(kvm, as_id);
+
 	/*
 	 * Note, the old memslot (and the pointer itself!) may be invalidated
 	 * and/or destroyed by kvm_set_memslot().
 	 */
-	old = id_to_memslot(__kvm_memslots(kvm, as_id), id);
+	old = id_to_memslot(slots, id);
 
 	if (!mem->memory_size) {
 		if (!old || !old->npages)
@@ -1894,18 +1920,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			return 0;
 	}
 
-	if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
-		int bkt;
-
-		/* Check for overlaps */
-		kvm_for_each_memslot(tmp, bkt, __kvm_memslots(kvm, as_id)) {
-			if (tmp->id == id)
-				continue;
-			if (!((new.base_gfn + new.npages <= tmp->base_gfn) ||
-			      (new.base_gfn >= tmp->base_gfn + tmp->npages)))
-				return -EEXIST;
-		}
-	}
+	if ((change == KVM_MR_CREATE || change == KVM_MR_MOVE) &&
+	    kvm_check_memslot_overlap(slots, id, new.base_gfn,
+				      new.base_gfn + new.npages))
+		return -EEXIST;
 
 	return kvm_set_memslot(kvm, old, &new, change);
 }
-- 
2.33.1.1089.g2158813163f-goog

[PATCH v5.5 29/30] KVM: Wait 'til the bitter end to initialize the "new" memslot

[Sean Christopherson]

Initialize the "new" memslot in the !DELETE path only after the various
sanity checks have passed.  This will allow a future commit to allocate
@new dynamically without having to copy a memslot, and without having to
deal with freeing @new in error paths and in the "nothing to change" path
that's hiding in the sanity checks.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 virt/kvm/kvm_main.c | 37 ++++++++++++++++++++-----------------
 1 file changed, 20 insertions(+), 17 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d22e40225703..5cc0b50faa8c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1838,6 +1838,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	struct kvm_memory_slot new;
 	struct kvm_memslots *slots;
 	enum kvm_mr_change change;
+	unsigned long npages;
+	gfn_t base_gfn;
 	int as_id, id;
 	int r;
 
@@ -1864,6 +1866,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		return -EINVAL;
 	if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
 		return -EINVAL;
+	if ((mem->memory_size >> PAGE_SHIFT) > KVM_MEM_MAX_NR_PAGES)
+		return -EINVAL;
 
 	slots = __kvm_memslots(kvm, as_id);
 
@@ -1887,15 +1891,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		return kvm_set_memslot(kvm, old, &new, KVM_MR_DELETE);
 	}
 
-	new.as_id = as_id;
-	new.id = id;
-	new.base_gfn = mem->guest_phys_addr >> PAGE_SHIFT;
-	new.npages = mem->memory_size >> PAGE_SHIFT;
-	new.flags = mem->flags;
-	new.userspace_addr = mem->userspace_addr;
-
-	if (new.npages > KVM_MEM_MAX_NR_PAGES)
-		return -EINVAL;
+	base_gfn = (mem->guest_phys_addr >> PAGE_SHIFT);
+	npages = (mem->memory_size >> PAGE_SHIFT);
 
 	if (!old || !old->npages) {
 		change = KVM_MR_CREATE;
@@ -1904,27 +1901,33 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		 * To simplify KVM internals, the total number of pages across
 		 * all memslots must fit in an unsigned long.
 		 */
-		if ((kvm->nr_memslot_pages + new.npages) < kvm->nr_memslot_pages)
+		if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
 			return -EINVAL;
 	} else { /* Modify an existing slot. */
-		if ((new.userspace_addr != old->userspace_addr) ||
-		    (new.npages != old->npages) ||
-		    ((new.flags ^ old->flags) & KVM_MEM_READONLY))
+		if ((mem->userspace_addr != old->userspace_addr) ||
+		    (npages != old->npages) ||
+		    ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
 			return -EINVAL;
 
-		if (new.base_gfn != old->base_gfn)
+		if (base_gfn != old->base_gfn)
 			change = KVM_MR_MOVE;
-		else if (new.flags != old->flags)
+		else if (mem->flags != old->flags)
 			change = KVM_MR_FLAGS_ONLY;
 		else /* Nothing to change. */
 			return 0;
 	}
 
 	if ((change == KVM_MR_CREATE || change == KVM_MR_MOVE) &&
-	    kvm_check_memslot_overlap(slots, id, new.base_gfn,
-				      new.base_gfn + new.npages))
+	    kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages))
 		return -EEXIST;
 
+	new.as_id = as_id;
+	new.id = id;
+	new.base_gfn = base_gfn;
+	new.npages = npages;
+	new.flags = mem->flags;
+	new.userspace_addr = mem->userspace_addr;
+
 	return kvm_set_memslot(kvm, old, &new, change);
 }
 EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 29/30] KVM: Wait 'til the bitter end to initialize the "new" memslot

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> Initialize the "new" memslot in the !DELETE path only after the various
> sanity checks have passed.  This will allow a future commit to allocate
> @new dynamically without having to copy a memslot, and without having to
> deal with freeing @new in error paths and in the "nothing to change" path
> that's hiding in the sanity checks.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---

Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

[PATCH v5.5 30/30] KVM: Dynamically allocate "new" memslots from the get-go

[Sean Christopherson]

Allocate the "new" memslot for !DELETE memslot updates straight away
instead of filling an intermediate on-stack object and forcing
kvm_set_memslot() to juggle the allocation and do weird things like reuse
the old memslot object in MOVE.

In the MOVE case, this results in an "extra" memslot allocation due to
allocating both the "new" slot and the "invalid" slot, but that's a
temporary and not-huge allocation, and MOVE is a relatively rare memslot
operation.

Regarding MOVE, drop the open-coded management of the gfn tree with a
call to kvm_replace_memslot(), which already handles the case where
new->base_gfn != old->base_gfn.  This is made possible by virtue of not
having to copy the "new" memslot data after erasing the old memslot from
the gfn tree.  Using kvm_replace_memslot(), and more specifically not
reusing the old memslot, means the MOVE case now does hva tree and hash
list updates, but that's a small price to pay for simplifying the code
and making MOVE align with all the other flavors of updates.  The "extra"
updates are firmly in the noise from a performance perspective, e.g. the
"move (in)active area" selfttests show a (very, very) slight improvement.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 virt/kvm/kvm_main.c | 178 +++++++++++++++++++-------------------------
 1 file changed, 77 insertions(+), 101 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5cc0b50faa8c..b413082c081d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1488,23 +1488,25 @@ static int kvm_prepare_memory_region(struct kvm *kvm,
 	 * new and KVM isn't using a ring buffer, allocate and initialize a
 	 * new bitmap.
 	 */
-	if (!(new->flags & KVM_MEM_LOG_DIRTY_PAGES))
-		new->dirty_bitmap = NULL;
-	else if (old->dirty_bitmap)
-		new->dirty_bitmap = old->dirty_bitmap;
-	else if (!kvm->dirty_ring_size) {
-		r = kvm_alloc_dirty_bitmap(new);
-		if (r)
-			return r;
+	if (change != KVM_MR_DELETE) {
+		if (!(new->flags & KVM_MEM_LOG_DIRTY_PAGES))
+			new->dirty_bitmap = NULL;
+		else if (old && old->dirty_bitmap)
+			new->dirty_bitmap = old->dirty_bitmap;
+		else if (!kvm->dirty_ring_size) {
+			r = kvm_alloc_dirty_bitmap(new);
+			if (r)
+				return r;
 
-		if (kvm_dirty_log_manual_protect_and_init_set(kvm))
-			bitmap_set(new->dirty_bitmap, 0, new->npages);
+			if (kvm_dirty_log_manual_protect_and_init_set(kvm))
+				bitmap_set(new->dirty_bitmap, 0, new->npages);
+		}
 	}
 
 	r = kvm_arch_prepare_memory_region(kvm, old, new, change);
 
 	/* Free the bitmap on failure if it was allocated above. */
-	if (r && new->dirty_bitmap && !old->dirty_bitmap)
+	if (r && new && new->dirty_bitmap && old && !old->dirty_bitmap)
 		kvm_destroy_dirty_bitmap(new);
 
 	return r;
@@ -1591,16 +1593,16 @@ static void kvm_copy_memslot(struct kvm_memory_slot *dest,
 
 static void kvm_invalidate_memslot(struct kvm *kvm,
 				   struct kvm_memory_slot *old,
-				   struct kvm_memory_slot *working_slot)
+				   struct kvm_memory_slot *invalid_slot)
 {
 	/*
 	 * Mark the current slot INVALID.  As with all memslot modifications,
 	 * this must be done on an unreachable slot to avoid modifying the
 	 * current slot in the active tree.
 	 */
-	kvm_copy_memslot(working_slot, old);
-	working_slot->flags |= KVM_MEMSLOT_INVALID;
-	kvm_replace_memslot(kvm, old, working_slot);
+	kvm_copy_memslot(invalid_slot, old);
+	invalid_slot->flags |= KVM_MEMSLOT_INVALID;
+	kvm_replace_memslot(kvm, old, invalid_slot);
 
 	/*
 	 * Activate the slot that is now marked INVALID, but don't propagate
@@ -1627,20 +1629,15 @@ static void kvm_invalidate_memslot(struct kvm *kvm,
 	 * above.  Writers are required to retrieve memslots *after* acquiring
 	 * slots_arch_lock, thus the active slot's data is guaranteed to be fresh.
 	 */
-	old->arch = working_slot->arch;
+	old->arch = invalid_slot->arch;
 }
 
 static void kvm_create_memslot(struct kvm *kvm,
-			       const struct kvm_memory_slot *new,
-			       struct kvm_memory_slot *working)
+			       struct kvm_memory_slot *new)
 {
-	/*
-	 * Add the new memslot to the inactive set as a copy of the
-	 * new memslot data provided by userspace.
-	 */
-	kvm_copy_memslot(working, new);
-	kvm_replace_memslot(kvm, NULL, working);
-	kvm_activate_memslot(kvm, NULL, working);
+	/* Add the new memslot to the inactive set and activate. */
+	kvm_replace_memslot(kvm, NULL, new);
+	kvm_activate_memslot(kvm, NULL, new);
 }
 
 static void kvm_delete_memslot(struct kvm *kvm,
@@ -1649,65 +1646,36 @@ static void kvm_delete_memslot(struct kvm *kvm,
 {
 	/*
 	 * Remove the old memslot (in the inactive memslots) by passing NULL as
-	 * the "new" slot.
+	 * the "new" slot, and for the invalid version in the active slots.
 	 */
 	kvm_replace_memslot(kvm, old, NULL);
-
-	/* And do the same for the invalid version in the active slot. */
 	kvm_activate_memslot(kvm, invalid_slot, NULL);
-
-	/* Free the invalid slot, the caller will clean up the old slot. */
-	kfree(invalid_slot);
 }
 
-static struct kvm_memory_slot *kvm_move_memslot(struct kvm *kvm,
-						struct kvm_memory_slot *old,
-						const struct kvm_memory_slot *new,
-						struct kvm_memory_slot *invalid_slot)
+static void kvm_move_memslot(struct kvm *kvm,
+			     struct kvm_memory_slot *old,
+			     struct kvm_memory_slot *new,
+			     struct kvm_memory_slot *invalid_slot)
 {
-	struct kvm_memslots *slots = kvm_get_inactive_memslots(kvm, old->as_id);
-
 	/*
-	 * The memslot's gfn is changing, remove it from the inactive tree, it
-	 * will be re-added with its updated gfn. Because its range is
-	 * changing, an in-place replace is not possible.
+	 * Replace the old memslot in the inactive slots, and then swap slots
+	 * and replace the current INVALID with the new as well.
 	 */
-	kvm_erase_gfn_node(slots, old);
-
-	/*
-	 * The old slot is now fully disconnected, reuse its memory for the
-	 * persistent copy of "new".
-	 */
-	kvm_copy_memslot(old, new);
-
-	/* Re-add to the gfn tree with the updated gfn */
-	kvm_insert_gfn_node(slots, old);
-
-	/* Replace the current INVALID slot with the updated memslot. */
-	kvm_activate_memslot(kvm, invalid_slot, old);
-
-	/*
-	 * Clear the INVALID flag so that the invalid_slot is now a perfect
-	 * copy of the old slot.  Return it for cleanup in the caller.
-	 */
-	WARN_ON_ONCE(!(invalid_slot->flags & KVM_MEMSLOT_INVALID));
-	invalid_slot->flags &= ~KVM_MEMSLOT_INVALID;
-	return invalid_slot;
+	kvm_replace_memslot(kvm, old, new);
+	kvm_activate_memslot(kvm, invalid_slot, new);
 }
 
 static void kvm_update_flags_memslot(struct kvm *kvm,
 				     struct kvm_memory_slot *old,
-				     const struct kvm_memory_slot *new,
-				     struct kvm_memory_slot *working_slot)
+				     struct kvm_memory_slot *new)
 {
 	/*
 	 * Similar to the MOVE case, but the slot doesn't need to be zapped as
 	 * an intermediate step. Instead, the old memslot is simply replaced
 	 * with a new, updated copy in both memslot sets.
 	 */
-	kvm_copy_memslot(working_slot, new);
-	kvm_replace_memslot(kvm, old, working_slot);
-	kvm_activate_memslot(kvm, old, working_slot);
+	kvm_replace_memslot(kvm, old, new);
+	kvm_activate_memslot(kvm, old, new);
 }
 
 static int kvm_set_memslot(struct kvm *kvm,
@@ -1715,19 +1683,9 @@ static int kvm_set_memslot(struct kvm *kvm,
 			   struct kvm_memory_slot *new,
 			   enum kvm_mr_change change)
 {
-	struct kvm_memory_slot *working;
+	struct kvm_memory_slot *invalid_slot;
 	int r;
 
-	/*
-	 * Modifications are done on an unreachable slot.  Any changes are then
-	 * (eventually) propagated to both the active and inactive slots.  This
-	 * allocation would ideally be on-demand (in helpers), but is done here
-	 * to avoid having to handle failure after kvm_prepare_memory_region().
-	 */
-	working = kzalloc(sizeof(*working), GFP_KERNEL_ACCOUNT);
-	if (!working)
-		return -ENOMEM;
-
 	/*
 	 * Released in kvm_swap_active_memslots.
 	 *
@@ -1752,9 +1710,19 @@ static int kvm_set_memslot(struct kvm *kvm,
 	 * (and without a lock), a window would exist between effecting the
 	 * delete/move and committing the changes in arch code where KVM or a
 	 * guest could access a non-existent memslot.
+	 *
+	 * Modifications are done on a temporary, unreachable slot.  The old
+	 * slot needs to be preserved in case a later step fails and the
+	 * invalidation needs to be reverted.
 	 */
-	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE)
-		kvm_invalidate_memslot(kvm, old, working);
+	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) {
+		invalid_slot = kzalloc(sizeof(*invalid_slot), GFP_KERNEL_ACCOUNT);
+		if (!invalid_slot) {
+			mutex_unlock(&kvm->slots_arch_lock);
+			return -ENOMEM;
+		}
+		kvm_invalidate_memslot(kvm, old, invalid_slot);
+	}
 
 	r = kvm_prepare_memory_region(kvm, old, new, change);
 	if (r) {
@@ -1764,11 +1732,12 @@ static int kvm_set_memslot(struct kvm *kvm,
 		 * in the inactive slots.  Changing the active memslots also
 		 * release slots_arch_lock.
 		 */
-		if (change == KVM_MR_DELETE || change == KVM_MR_MOVE)
-			kvm_activate_memslot(kvm, working, old);
-		else
+		if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) {
+			kvm_activate_memslot(kvm, invalid_slot, old);
+			kfree(invalid_slot);
+		} else {
 			mutex_unlock(&kvm->slots_arch_lock);
-		kfree(working);
+		}
 		return r;
 	}
 
@@ -1780,16 +1749,20 @@ static int kvm_set_memslot(struct kvm *kvm,
 	 * old slot is detached but otherwise preserved.
 	 */
 	if (change == KVM_MR_CREATE)
-		kvm_create_memslot(kvm, new, working);
+		kvm_create_memslot(kvm, new);
 	else if (change == KVM_MR_DELETE)
-		kvm_delete_memslot(kvm, old, working);
+		kvm_delete_memslot(kvm, old, invalid_slot);
 	else if (change == KVM_MR_MOVE)
-		old = kvm_move_memslot(kvm, old, new, working);
+		kvm_move_memslot(kvm, old, new, invalid_slot);
 	else if (change == KVM_MR_FLAGS_ONLY)
-		kvm_update_flags_memslot(kvm, old, new, working);
+		kvm_update_flags_memslot(kvm, old, new);
 	else
 		BUG();
 
+	/* Free the temporary INVALID slot used for DELETE and MOVE. */
+	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE)
+		kfree(invalid_slot);
+
 	/*
 	 * No need to refresh new->arch, changes after dropping slots_arch_lock
 	 * will directly hit the final, active memsot.  Architectures are
@@ -1834,8 +1807,7 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
 int __kvm_set_memory_region(struct kvm *kvm,
 			    const struct kvm_userspace_memory_region *mem)
 {
-	struct kvm_memory_slot *old;
-	struct kvm_memory_slot new;
+	struct kvm_memory_slot *old, *new;
 	struct kvm_memslots *slots;
 	enum kvm_mr_change change;
 	unsigned long npages;
@@ -1884,11 +1856,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		if (WARN_ON_ONCE(kvm->nr_memslot_pages < old->npages))
 			return -EIO;
 
-		memset(&new, 0, sizeof(new));
-		new.id = id;
-		new.as_id = as_id;
-
-		return kvm_set_memslot(kvm, old, &new, KVM_MR_DELETE);
+		return kvm_set_memslot(kvm, old, NULL, KVM_MR_DELETE);
 	}
 
 	base_gfn = (mem->guest_phys_addr >> PAGE_SHIFT);
@@ -1921,14 +1889,22 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	    kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages))
 		return -EEXIST;
 
-	new.as_id = as_id;
-	new.id = id;
-	new.base_gfn = base_gfn;
-	new.npages = npages;
-	new.flags = mem->flags;
-	new.userspace_addr = mem->userspace_addr;
+	/* Allocate a slot that will persist in the memslot. */
+	new = kzalloc(sizeof(*new), GFP_KERNEL_ACCOUNT);
+	if (!new)
+		return -ENOMEM;
 
-	return kvm_set_memslot(kvm, old, &new, change);
+	new->as_id = as_id;
+	new->id = id;
+	new->base_gfn = base_gfn;
+	new->npages = npages;
+	new->flags = mem->flags;
+	new->userspace_addr = mem->userspace_addr;
+
+	r = kvm_set_memslot(kvm, old, new, change);
+	if (r)
+		kfree(new);
+	return r;
 }
 EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
 
-- 
2.33.1.1089.g2158813163f-goog

Re: [PATCH v5.5 30/30] KVM: Dynamically allocate "new" memslots from the get-go

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> Allocate the "new" memslot for !DELETE memslot updates straight away
> instead of filling an intermediate on-stack object and forcing
> kvm_set_memslot() to juggle the allocation and do weird things like reuse
> the old memslot object in MOVE.
> 
> In the MOVE case, this results in an "extra" memslot allocation due to
> allocating both the "new" slot and the "invalid" slot, but that's a
> temporary and not-huge allocation, and MOVE is a relatively rare memslot
> operation.
> 
> Regarding MOVE, drop the open-coded management of the gfn tree with a
> call to kvm_replace_memslot(), which already handles the case where
> new->base_gfn != old->base_gfn.  This is made possible by virtue of not
> having to copy the "new" memslot data after erasing the old memslot from
> the gfn tree.  Using kvm_replace_memslot(), and more specifically not
> reusing the old memslot, means the MOVE case now does hva tree and hash
> list updates, but that's a small price to pay for simplifying the code
> and making MOVE align with all the other flavors of updates.  The "extra"
> updates are firmly in the noise from a performance perspective, e.g. the
> "move (in)active area" selfttests show a (very, very) slight improvement.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

For a new patch set version when the "main" commit is rewritten anyway
(I mean the one titled "Keep memslots in tree-based structures instead of
array-based ones") it makes sense to integrate changes like these into
such modified main commit.

This way a full algorithm / logic check for all the supported memslot
operations needs to be done only once instead of having to be done
multiple times for all these intermediate forms of the code (as this is
a quite time-consuming job to do properly).

I think it only makes sense to separate non-functional changes (like
renaming of variables, comment rewording, open-coding a helper, etc.)
into their own patches for ease of reviewing.

Or if the main commit was unchanged from the last reviewed version so
actual changes in the new version will stand out.

Thanks,
Maciej

Re: [PATCH v5.5 30/30] KVM: Dynamically allocate "new" memslots from the get-go

[Sean Christopherson]

On Fri, Nov 12, 2021, Maciej S. Szmigiero wrote:
> On 04.11.2021 01:25, Sean Christopherson wrote:
> > Allocate the "new" memslot for !DELETE memslot updates straight away
> > instead of filling an intermediate on-stack object and forcing
> > kvm_set_memslot() to juggle the allocation and do weird things like reuse
> > the old memslot object in MOVE.
> > 
> > In the MOVE case, this results in an "extra" memslot allocation due to
> > allocating both the "new" slot and the "invalid" slot, but that's a
> > temporary and not-huge allocation, and MOVE is a relatively rare memslot
> > operation.
> > 
> > Regarding MOVE, drop the open-coded management of the gfn tree with a
> > call to kvm_replace_memslot(), which already handles the case where
> > new->base_gfn != old->base_gfn.  This is made possible by virtue of not
> > having to copy the "new" memslot data after erasing the old memslot from
> > the gfn tree.  Using kvm_replace_memslot(), and more specifically not
> > reusing the old memslot, means the MOVE case now does hva tree and hash
> > list updates, but that's a small price to pay for simplifying the code
> > and making MOVE align with all the other flavors of updates.  The "extra"
> > updates are firmly in the noise from a performance perspective, e.g. the
> > "move (in)active area" selfttests show a (very, very) slight improvement.
> > 
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> 
> Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> 
> For a new patch set version when the "main" commit is rewritten anyway
> (I mean the one titled "Keep memslots in tree-based structures instead of
> array-based ones") it makes sense to integrate changes like these into
> such modified main commit.
> 
> This way a full algorithm / logic check for all the supported memslot
> operations needs to be done only once instead of having to be done
> multiple times for all these intermediate forms of the code (as this is
> a quite time-consuming job to do properly).
> 
> I think it only makes sense to separate non-functional changes (like
> renaming of variables, comment rewording, open-coding a helper, etc.)
> into their own patches for ease of reviewing.

I agree that validating intermediate stages is time-consuming and can be
frustrating, but that doesn't diminish the value of intermediate patches.  I do
tend to lean too far towards slicing and dicing, but I am quite confident that
I've come out ahead in terms of time spent validating smaller patches versus
time saved because bisection could pinpoint the exact problem.

E.g. in this patch, arch code can now see a NULL @new.  That's _supposed_ to be a
non-functional change, but it would be all too easy to have missed a path in the
prep work where an arch accesses @new without first checking it for NULL (or DELETE).
If such a bug were to escape review, then bisection would point at this patch, not
the mega patch that completely reworked the core memslots behavior.

And IIRC, I actually botched the prior "bitter end" patch and initially missed a
new.npages => npages conversion.  Again, no functional change _intended_, but one
of the main reasons for doing small(er) intermediate patches is precisely so that
any unintended behavior stands out and is easier to debug/triage.

> Or if the main commit was unchanged from the last reviewed version so
> actual changes in the new version will stand out.
> 
> Thanks,
> Maciej

Re: [PATCH v5.5 00/30] KVM: Scalable memslots implementation

[Maciej S. Szmigiero]

On 04.11.2021 01:25, Sean Christopherson wrote:
> This series is an iteration of Maciej's scalable memslots work.  It
> addresses most, but not all, of my feedback from v5, hence the "5.5"
> moniker.  Specifically, I did not touch the iteration over gfn and hva
> ranges as I would likely do more harm than good, especially in the gfn
> iterator.
> 
> The core functionality of the series is unchanged from v5 (or at least,
> it should be).  Patches "Resolve memslot ID via a hash table" and "Keep
> memslots in tree-based structures" are heavily reworked (the latter in
> particular) to provide better continuity between patches and to avoid
> the swap() logic when working with the "inactive" set of memslots.  But
> again, the changes are intended to be purely cosmetic.
> 
> Paolo, ideally I'd like get to patch 03 (and therefore patch 02) into 5.16.
> The patch technically breaks backwards compatibility with 32-bit KVM, but
> I'm quite confident none of the existing 32-bit architectures can possibly
> work.  RISC-V is the one exception where it's not obvious that creating
> more guest memslot pages than can fit in an unsigned long won't fall on its
> face.  Since RISC-V is new in 5.16, I'd like to get that change in before
> RISC-V can gain any users doing bizarre things.
> 
> s390 folks, please look closely at patch 11, "KVM: s390: Use "new" memslot
> instead of userspace memory region".  There's a subtle/weird functional
> change in there that I can't imagine would negatively affect userspace,
> but the end result is odd nonetheless.
> 
> Claudio, I dropped your R-b from "KVM: Integrate gfn_to_memslot_approx()
> into search_memslots()" because I changed the code enough to break the s390
> build at least once :-)
> 
> Patches 01 and 02 are bug fixes.
> 
> Patch 03 is fix of sorts to require that the total number of pages across
> all memslots fit in an unsigned long.  The existing 32-bit KVM
> architectures don't correctly handle this case, and fixing those issues
> would quite gross and a waste of time.
> 
> Patches 04-18 are cleanups throughout common KVM and all architectures
> to fix some warts in the memslot APIs that allow for a cleaner (IMO)
> of the tree-based memslots code.  They also prep for more improvements
> that are realized in the final patch.
> 
> Patches 19-28 are the core of Maciej's scalable memslots work.
> 
> Patches 29-30 take advantage of the tree-based memslots to avoid creating
> a dummy "new" memslot on the stack, which simplifies the MOVE case and
> aligns it with the other three memslot update cases.

Thanks for the updated series Sean - that's an impressive amount of
cleanups for the existing KVM code.

I've reviewed the non-arch-specific and x86-specific patches till patch 22
(inclusive).
Further patches are more invasive and require a more through review -
will try to do this in coming days.

The arch-specific but non-x86-ones patches look OK to me, too, at the
first glance but here it would be better if maintainers or reviewers
from particular arch gave their acks.

By the way, do you want your patches and my non-invasive patches (patches
below number 23) merged without waiting for the rest of the series to be
fully ready?

This way there is less risk of conflicting changes to KVM being merged
in meantime while we are still discussing the remaining patches.
Or worse - changes that don't conflict but subtly break some assumptions
that the code relies on.

For this reason I am strongly for merging them independently from the
more invasive parts.

Thanks,
Maciej

Re: [PATCH v5.5 00/30] KVM: Scalable memslots implementation

[Sean Christopherson]

On Tue, Nov 09, 2021, Maciej S. Szmigiero wrote:
> On 04.11.2021 01:25, Sean Christopherson wrote:
> By the way, do you want your patches and my non-invasive patches (patches
> below number 23) merged without waiting for the rest of the series to be
> fully ready?
> 
> This way there is less risk of conflicting changes to KVM being merged
> in meantime while we are still discussing the remaining patches.
> Or worse - changes that don't conflict but subtly break some assumptions
> that the code relies on.
> 
> For this reason I am strongly for merging them independently from the
> more invasive parts.

Merging them as soon as they're ready would also be my preference.  That said,
I'm hoping we can get the entire implemenation queued up for 5.17 sooner than
later.  I'll do my best to respond quickly to try and make that happen.

Re: [PATCH v5.5 00/30] KVM: Scalable memslots implementation

[Maciej S. Szmigiero]

On 09.11.2021 02:21, Sean Christopherson wrote:
> On Tue, Nov 09, 2021, Maciej S. Szmigiero wrote:
>> On 04.11.2021 01:25, Sean Christopherson wrote:
>> By the way, do you want your patches and my non-invasive patches (patches
>> below number 23) merged without waiting for the rest of the series to be
>> fully ready?
>>
>> This way there is less risk of conflicting changes to KVM being merged
>> in meantime while we are still discussing the remaining patches.
>> Or worse - changes that don't conflict but subtly break some assumptions
>> that the code relies on.
>>
>> For this reason I am strongly for merging them independently from the
>> more invasive parts.
> 
> Merging them as soon as they're ready would also be my preference.  That said,
> I'm hoping we can get the entire implemenation queued up for 5.17 sooner than
> later.  I'll do my best to respond quickly to try and make that happen.
> 

Finished going through all the patches, with small nits they do make sense
to me - thanks Sean.

I will prepare an updated (and tested!) next version of this patch set,
however this may take about two+ weeks as I have other, more urgent work
to do right now.

Thanks,
Maciej

Re: [PATCH v5.5 00/30] KVM: Scalable memslots implementation

[Maciej S. Szmigiero]

Paolo,

I see that you have merged the whole series to kvm/queue, even though it
still needed some changes and, most importantly, a good round of testing.

Does this mean you want all these changes as a separate patch set on top
of the already-merged series?

Thanks,
Maciej

Re: [PATCH v5.5 00/30] KVM: Scalable memslots implementation

[Paolo Bonzini]

On 11/23/21 15:42, Maciej S. Szmigiero wrote:
> Paolo,
> 
> I see that you have merged the whole series to kvm/queue, even though it
> still needed some changes and, most importantly, a good round of testing.
> 
> Does this mean you want all these changes as a separate patch set on top
> of the already-merged series?

Hi Maciej,

you can squash your changes and post a v6.

Paolo