* [PATCH v2 0/3] KVM: MMU: Fix a refcount bug with ZONE_DEVICE pages
@ 2019-11-11 22:12 Sean Christopherson
2019-11-11 22:12 ` [PATCH v2 1/3] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved Sean Christopherson
` (2 more replies)
0 siblings, 3 replies; 8+ messages in thread
From: Sean Christopherson @ 2019-11-11 22:12 UTC (permalink / raw)
To: Paolo Bonzini, Radim Krčmář
Cc: Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel, kvm, linux-kernel, Adam Borowski,
David Hildenbrand, Dan Williams
This mini-series fixes a suspected, but technically unconfirmed, bug in
KVM related to ZONE_DEVICE pages. The suspected issue is that KVM treats
ZONE_DEVICE pages as reserved PFNs, and so doesn't put references to such
pages when dropping references via KVM's generic kvm_release_pfn_clean().
David Hildenbrand uncovered the bug during a discussion about removing
PG_reserved from ZONE_DEVICE pages, after Dan Williams pointed out[1] that
there was a bug report from Adam Borowski[2] that was likely related to
KVM's interaction with PageReserved().
Patch 1/3 contains the actual fix, patches 2/3 and 3/3 are minor cleanup
that is mostly unrelated, but dependent and prompted by the fix itself.
v2:
- Remove the kvm_is_zone_device_pfn(pfn) check from kvm_get_pfn(). It's
not entirely clear whether or not the hva_to_pfn_remapped() case is
actually broken, e.g. KVM's page fault handler is likely ok, whereas
not calling get_page() willl definitely cause breakage as KVM would
later call put_page() on the pfn/page. [Paolo]
- WARN if kvm_is_zone_device_pfn() is called without the underlying
page being pinned. This won't necessarily catch all bugs, e.g. if
the above hva_to_pfn_remapped case is indeed broken, but will
prevent completely bogus usage. [Dan]
- Remove the is_error_pfn() check from transparent_hugepage_adjust()
instead of carrying it forward into the new kvm_is_hugepage_allowed()
helper. [Paolo]
[1] http://lkml.kernel.org/r/20190919115547.GA17963@angband.pl
[2] https://lkml.kernel.org/r/01adb4cb-6092-638c-0bab-e61322be7cf5@redhat.com
Sean Christopherson (3):
KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved
KVM: x86/mmu: Remove superfluous is_error_pfn() check from THP adjust
KVM: x86/mmu: Add helper to consolidate huge page promotion
arch/x86/kvm/mmu.c | 15 +++++++++------
include/linux/kvm_host.h | 1 +
virt/kvm/kvm_main.c | 26 +++++++++++++++++++++++---
3 files changed, 33 insertions(+), 9 deletions(-)
--
2.24.0
^ permalink raw reply [flat|nested] 8+ messages in thread
* [PATCH v2 1/3] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved
2019-11-11 22:12 [PATCH v2 0/3] KVM: MMU: Fix a refcount bug with ZONE_DEVICE pages Sean Christopherson
@ 2019-11-11 22:12 ` Sean Christopherson
2019-11-11 22:20 ` Paolo Bonzini
` (2 more replies)
2019-11-11 22:12 ` [PATCH v2 2/3] KVM: x86/mmu: Remove superfluous is_error_pfn() check from THP adjust Sean Christopherson
2019-11-11 22:12 ` [PATCH v2 3/3] KVM: x86/mmu: Add helper to consolidate huge page promotion Sean Christopherson
2 siblings, 3 replies; 8+ messages in thread
From: Sean Christopherson @ 2019-11-11 22:12 UTC (permalink / raw)
To: Paolo Bonzini, Radim Krčmář
Cc: Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel, kvm, linux-kernel, Adam Borowski,
David Hildenbrand, Dan Williams
Explicitly exempt ZONE_DEVICE pages from kvm_is_reserved_pfn() and
instead manually handle ZONE_DEVICE on a case-by-case basis. For things
like page refcounts, KVM needs to treat ZONE_DEVICE pages like normal
pages, e.g. put pages grabbed via gup(). But for flows such as setting
A/D bits or shifting refcounts for transparent huge pages, KVM needs to
to avoid processing ZONE_DEVICE pages as the flows in question lack the
underlying machinery for proper handling of ZONE_DEVICE pages.
This fixes a hang reported by Adam Borowski[*] in dev_pagemap_cleanup()
when running a KVM guest backed with /dev/dax memory, as KVM straight up
doesn't put any references to ZONE_DEVICE pages acquired by gup().
Note, Dan Williams proposed an alternative solution of doing put_page()
on ZONE_DEVICE pages immediately after gup() in order to simplify the
auditing needed to ensure is_zone_device_page() is called if and only if
the backing device is pinned (via gup()). But that approach would break
kvm_vcpu_{un}map() as KVM requires the page to be pinned from map() 'til
unmap() when accessing guest memory, unlike KVM's secondary MMU, which
coordinates with mmu_notifier invalidations to avoid creating stale
page references, i.e. doesn't rely on pages being pinned.
[*] http://lkml.kernel.org/r/20190919115547.GA17963@angband.pl
Reported-by: Adam Borowski <kilobyte@angband.pl>
Debugged-by: David Hildenbrand <david@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/mmu.c | 8 ++++----
include/linux/kvm_host.h | 1 +
virt/kvm/kvm_main.c | 26 +++++++++++++++++++++++---
3 files changed, 28 insertions(+), 7 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 24c23c66b226..bf82b1f2e834 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3306,7 +3306,7 @@ static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu,
* here.
*/
if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) &&
- level == PT_PAGE_TABLE_LEVEL &&
+ !kvm_is_zone_device_pfn(pfn) && level == PT_PAGE_TABLE_LEVEL &&
PageTransCompoundMap(pfn_to_page(pfn)) &&
!mmu_gfn_lpage_is_disallowed(vcpu, gfn, PT_DIRECTORY_LEVEL)) {
unsigned long mask;
@@ -5914,9 +5914,9 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
* the guest, and the guest page table is using 4K page size
* mapping if the indirect sp has level = 1.
*/
- if (sp->role.direct &&
- !kvm_is_reserved_pfn(pfn) &&
- PageTransCompoundMap(pfn_to_page(pfn))) {
+ if (sp->role.direct && !kvm_is_reserved_pfn(pfn) &&
+ !kvm_is_zone_device_pfn(pfn) &&
+ PageTransCompoundMap(pfn_to_page(pfn))) {
pte_list_remove(rmap_head, sptep);
if (kvm_available_flush_tlb_with_range())
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index a817e446c9aa..4ad1cd7d2d4d 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -966,6 +966,7 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu);
void kvm_vcpu_kick(struct kvm_vcpu *vcpu);
bool kvm_is_reserved_pfn(kvm_pfn_t pfn);
+bool kvm_is_zone_device_pfn(kvm_pfn_t pfn);
struct kvm_irq_ack_notifier {
struct hlist_node link;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b8534c6b8cf6..bc9d10a0a334 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -149,10 +149,30 @@ __weak int kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
return 0;
}
+bool kvm_is_zone_device_pfn(kvm_pfn_t pfn)
+{
+ /*
+ * The metadata used by is_zone_device_page() to determine whether or
+ * not a page is ZONE_DEVICE is guaranteed to be valid if and only if
+ * the device has been pinned, e.g. by get_user_pages(). WARN if the
+ * page_count() is zero to help detect bad usage of this helper.
+ */
+ if (!pfn_valid(pfn) || WARN_ON_ONCE(!page_count(pfn_to_page(pfn))))
+ return false;
+
+ return is_zone_device_page(pfn_to_page(pfn));
+}
+
bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
{
+ /*
+ * ZONE_DEVICE pages currently set PG_reserved, but from a refcounting
+ * perspective they are "normal" pages, albeit with slightly different
+ * usage rules.
+ */
if (pfn_valid(pfn))
- return PageReserved(pfn_to_page(pfn));
+ return PageReserved(pfn_to_page(pfn)) &&
+ !kvm_is_zone_device_pfn(pfn);
return true;
}
@@ -1865,7 +1885,7 @@ EXPORT_SYMBOL_GPL(kvm_release_pfn_dirty);
void kvm_set_pfn_dirty(kvm_pfn_t pfn)
{
- if (!kvm_is_reserved_pfn(pfn)) {
+ if (!kvm_is_reserved_pfn(pfn) && !kvm_is_zone_device_pfn(pfn)) {
struct page *page = pfn_to_page(pfn);
SetPageDirty(page);
@@ -1875,7 +1895,7 @@ EXPORT_SYMBOL_GPL(kvm_set_pfn_dirty);
void kvm_set_pfn_accessed(kvm_pfn_t pfn)
{
- if (!kvm_is_reserved_pfn(pfn))
+ if (!kvm_is_reserved_pfn(pfn) && !kvm_is_zone_device_pfn(pfn))
mark_page_accessed(pfn_to_page(pfn));
}
EXPORT_SYMBOL_GPL(kvm_set_pfn_accessed);
--
2.24.0
^ permalink raw reply related [flat|nested] 8+ messages in thread
* [PATCH v2 2/3] KVM: x86/mmu: Remove superfluous is_error_pfn() check from THP adjust
2019-11-11 22:12 [PATCH v2 0/3] KVM: MMU: Fix a refcount bug with ZONE_DEVICE pages Sean Christopherson
2019-11-11 22:12 ` [PATCH v2 1/3] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved Sean Christopherson
@ 2019-11-11 22:12 ` Sean Christopherson
2019-11-11 22:12 ` [PATCH v2 3/3] KVM: x86/mmu: Add helper to consolidate huge page promotion Sean Christopherson
2 siblings, 0 replies; 8+ messages in thread
From: Sean Christopherson @ 2019-11-11 22:12 UTC (permalink / raw)
To: Paolo Bonzini, Radim Krčmář
Cc: Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel, kvm, linux-kernel, Adam Borowski,
David Hildenbrand, Dan Williams
Replace the is_error_noslot_pfn() check in transparent_hugepage_adjust()
with an is_noslot_pfn() check. thp_adjust() cannot be reached with an
error pfn as it is always called after handle_abnormal_pfn(), which
aborts the page fault handler if an error pfn is encountered. Don't
bother future proofing thp_adjust() with a WARN on is_error_pfn(), as
calling thp_adjust() before handle_abnormal_pfn() is impossible for all
intents and purposes, e.g. thp_adjust() relies on being called after
mmu_notifier_retry() and while holding mmu_lock, thus moving it would
essentially require a complete rewrite of KVM's page fault handlers.
No functional change intended.
Reported-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/mmu.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index bf82b1f2e834..c35c6fb2635a 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3305,7 +3305,7 @@ static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu,
* PT_PAGE_TABLE_LEVEL and there would be no adjustment done
* here.
*/
- if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) &&
+ if (!is_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) &&
!kvm_is_zone_device_pfn(pfn) && level == PT_PAGE_TABLE_LEVEL &&
PageTransCompoundMap(pfn_to_page(pfn)) &&
!mmu_gfn_lpage_is_disallowed(vcpu, gfn, PT_DIRECTORY_LEVEL)) {
--
2.24.0
^ permalink raw reply related [flat|nested] 8+ messages in thread
* [PATCH v2 3/3] KVM: x86/mmu: Add helper to consolidate huge page promotion
2019-11-11 22:12 [PATCH v2 0/3] KVM: MMU: Fix a refcount bug with ZONE_DEVICE pages Sean Christopherson
2019-11-11 22:12 ` [PATCH v2 1/3] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved Sean Christopherson
2019-11-11 22:12 ` [PATCH v2 2/3] KVM: x86/mmu: Remove superfluous is_error_pfn() check from THP adjust Sean Christopherson
@ 2019-11-11 22:12 ` Sean Christopherson
2 siblings, 0 replies; 8+ messages in thread
From: Sean Christopherson @ 2019-11-11 22:12 UTC (permalink / raw)
To: Paolo Bonzini, Radim Krčmář
Cc: Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel, kvm, linux-kernel, Adam Borowski,
David Hildenbrand, Dan Williams
Add a helper, kvm_is_hugepage_allowed(), to consolidate identical code
across transparent_hugepage_adjust() and kvm_mmu_zap_collapsible_spte().
No functional change intended.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/mmu.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index c35c6fb2635a..95163f3abb24 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3292,6 +3292,12 @@ static int kvm_handle_bad_page(struct kvm_vcpu *vcpu, gfn_t gfn, kvm_pfn_t pfn)
return -EFAULT;
}
+static bool kvm_is_hugepage_allowed(kvm_pfn_t pfn)
+{
+ return !kvm_is_reserved_pfn(pfn) && !kvm_is_zone_device_pfn(pfn) &&
+ PageTransCompoundMap(pfn_to_page(pfn));
+}
+
static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu,
gfn_t gfn, kvm_pfn_t *pfnp,
int *levelp)
@@ -3305,9 +3311,8 @@ static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu,
* PT_PAGE_TABLE_LEVEL and there would be no adjustment done
* here.
*/
- if (!is_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) &&
- !kvm_is_zone_device_pfn(pfn) && level == PT_PAGE_TABLE_LEVEL &&
- PageTransCompoundMap(pfn_to_page(pfn)) &&
+ if (!is_noslot_pfn(pfn) && level == PT_PAGE_TABLE_LEVEL &&
+ kvm_is_hugepage_allowed(pfn) &&
!mmu_gfn_lpage_is_disallowed(vcpu, gfn, PT_DIRECTORY_LEVEL)) {
unsigned long mask;
/*
@@ -5914,9 +5919,7 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
* the guest, and the guest page table is using 4K page size
* mapping if the indirect sp has level = 1.
*/
- if (sp->role.direct && !kvm_is_reserved_pfn(pfn) &&
- !kvm_is_zone_device_pfn(pfn) &&
- PageTransCompoundMap(pfn_to_page(pfn))) {
+ if (sp->role.direct && kvm_is_hugepage_allowed(pfn)) {
pte_list_remove(rmap_head, sptep);
if (kvm_available_flush_tlb_with_range())
--
2.24.0
^ permalink raw reply related [flat|nested] 8+ messages in thread
* Re: [PATCH v2 1/3] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved
2019-11-11 22:12 ` [PATCH v2 1/3] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved Sean Christopherson
@ 2019-11-11 22:20 ` Paolo Bonzini
2019-11-11 22:39 ` Dan Williams
2019-11-12 7:06 ` David Hildenbrand
2 siblings, 0 replies; 8+ messages in thread
From: Paolo Bonzini @ 2019-11-11 22:20 UTC (permalink / raw)
To: Sean Christopherson, Radim Krčmář
Cc: Vitaly Kuznetsov, Wanpeng Li, Jim Mattson, Joerg Roedel, kvm,
linux-kernel, Adam Borowski, David Hildenbrand, Dan Williams
On 11/11/19 23:12, Sean Christopherson wrote:
> Explicitly exempt ZONE_DEVICE pages from kvm_is_reserved_pfn() and
> instead manually handle ZONE_DEVICE on a case-by-case basis. For things
> like page refcounts, KVM needs to treat ZONE_DEVICE pages like normal
> pages, e.g. put pages grabbed via gup(). But for flows such as setting
> A/D bits or shifting refcounts for transparent huge pages, KVM needs to
> to avoid processing ZONE_DEVICE pages as the flows in question lack the
> underlying machinery for proper handling of ZONE_DEVICE pages.
>
> This fixes a hang reported by Adam Borowski[*] in dev_pagemap_cleanup()
> when running a KVM guest backed with /dev/dax memory, as KVM straight up
> doesn't put any references to ZONE_DEVICE pages acquired by gup().
>
> Note, Dan Williams proposed an alternative solution of doing put_page()
> on ZONE_DEVICE pages immediately after gup() in order to simplify the
> auditing needed to ensure is_zone_device_page() is called if and only if
> the backing device is pinned (via gup()). But that approach would break
> kvm_vcpu_{un}map() as KVM requires the page to be pinned from map() 'til
> unmap() when accessing guest memory, unlike KVM's secondary MMU, which
> coordinates with mmu_notifier invalidations to avoid creating stale
> page references, i.e. doesn't rely on pages being pinned.
>
> [*] http://lkml.kernel.org/r/20190919115547.GA17963@angband.pl
>
> Reported-by: Adam Borowski <kilobyte@angband.pl>
> Debugged-by: David Hildenbrand <david@redhat.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> arch/x86/kvm/mmu.c | 8 ++++----
> include/linux/kvm_host.h | 1 +
> virt/kvm/kvm_main.c | 26 +++++++++++++++++++++++---
> 3 files changed, 28 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 24c23c66b226..bf82b1f2e834 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -3306,7 +3306,7 @@ static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu,
> * here.
> */
> if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) &&
> - level == PT_PAGE_TABLE_LEVEL &&
> + !kvm_is_zone_device_pfn(pfn) && level == PT_PAGE_TABLE_LEVEL &&
> PageTransCompoundMap(pfn_to_page(pfn)) &&
> !mmu_gfn_lpage_is_disallowed(vcpu, gfn, PT_DIRECTORY_LEVEL)) {
> unsigned long mask;
> @@ -5914,9 +5914,9 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
> * the guest, and the guest page table is using 4K page size
> * mapping if the indirect sp has level = 1.
> */
> - if (sp->role.direct &&
> - !kvm_is_reserved_pfn(pfn) &&
> - PageTransCompoundMap(pfn_to_page(pfn))) {
> + if (sp->role.direct && !kvm_is_reserved_pfn(pfn) &&
> + !kvm_is_zone_device_pfn(pfn) &&
> + PageTransCompoundMap(pfn_to_page(pfn))) {
> pte_list_remove(rmap_head, sptep);
>
> if (kvm_available_flush_tlb_with_range())
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index a817e446c9aa..4ad1cd7d2d4d 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -966,6 +966,7 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu);
> void kvm_vcpu_kick(struct kvm_vcpu *vcpu);
>
> bool kvm_is_reserved_pfn(kvm_pfn_t pfn);
> +bool kvm_is_zone_device_pfn(kvm_pfn_t pfn);
>
> struct kvm_irq_ack_notifier {
> struct hlist_node link;
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index b8534c6b8cf6..bc9d10a0a334 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -149,10 +149,30 @@ __weak int kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
> return 0;
> }
>
> +bool kvm_is_zone_device_pfn(kvm_pfn_t pfn)
> +{
> + /*
> + * The metadata used by is_zone_device_page() to determine whether or
> + * not a page is ZONE_DEVICE is guaranteed to be valid if and only if
> + * the device has been pinned, e.g. by get_user_pages(). WARN if the
> + * page_count() is zero to help detect bad usage of this helper.
> + */
> + if (!pfn_valid(pfn) || WARN_ON_ONCE(!page_count(pfn_to_page(pfn))))
> + return false;
> +
> + return is_zone_device_page(pfn_to_page(pfn));
> +}
> +
> bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
> {
> + /*
> + * ZONE_DEVICE pages currently set PG_reserved, but from a refcounting
> + * perspective they are "normal" pages, albeit with slightly different
> + * usage rules.
> + */
> if (pfn_valid(pfn))
> - return PageReserved(pfn_to_page(pfn));
> + return PageReserved(pfn_to_page(pfn)) &&
> + !kvm_is_zone_device_pfn(pfn);
>
> return true;
> }
> @@ -1865,7 +1885,7 @@ EXPORT_SYMBOL_GPL(kvm_release_pfn_dirty);
>
> void kvm_set_pfn_dirty(kvm_pfn_t pfn)
> {
> - if (!kvm_is_reserved_pfn(pfn)) {
> + if (!kvm_is_reserved_pfn(pfn) && !kvm_is_zone_device_pfn(pfn)) {
> struct page *page = pfn_to_page(pfn);
>
> SetPageDirty(page);
> @@ -1875,7 +1895,7 @@ EXPORT_SYMBOL_GPL(kvm_set_pfn_dirty);
>
> void kvm_set_pfn_accessed(kvm_pfn_t pfn)
> {
> - if (!kvm_is_reserved_pfn(pfn))
> + if (!kvm_is_reserved_pfn(pfn) && !kvm_is_zone_device_pfn(pfn))
> mark_page_accessed(pfn_to_page(pfn));
> }
> EXPORT_SYMBOL_GPL(kvm_set_pfn_accessed);
>
Queued, thanks -- the other two will wait for after the merge window to
avoid pointless conflicts.
Paolo
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH v2 1/3] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved
2019-11-11 22:12 ` [PATCH v2 1/3] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved Sean Christopherson
2019-11-11 22:20 ` Paolo Bonzini
@ 2019-11-11 22:39 ` Dan Williams
2019-11-11 22:43 ` Paolo Bonzini
2019-11-12 7:06 ` David Hildenbrand
2 siblings, 1 reply; 8+ messages in thread
From: Dan Williams @ 2019-11-11 22:39 UTC (permalink / raw)
To: Sean Christopherson
Cc: Paolo Bonzini, Radim Krčmář,
Vitaly Kuznetsov, Wanpeng Li, Jim Mattson, Joerg Roedel,
KVM list, Linux Kernel Mailing List, Adam Borowski,
David Hildenbrand
On Mon, Nov 11, 2019 at 2:12 PM Sean Christopherson
<sean.j.christopherson@intel.com> wrote:
>
> Explicitly exempt ZONE_DEVICE pages from kvm_is_reserved_pfn() and
> instead manually handle ZONE_DEVICE on a case-by-case basis. For things
> like page refcounts, KVM needs to treat ZONE_DEVICE pages like normal
> pages, e.g. put pages grabbed via gup(). But for flows such as setting
> A/D bits or shifting refcounts for transparent huge pages, KVM needs to
> to avoid processing ZONE_DEVICE pages as the flows in question lack the
> underlying machinery for proper handling of ZONE_DEVICE pages.
>
> This fixes a hang reported by Adam Borowski[*] in dev_pagemap_cleanup()
> when running a KVM guest backed with /dev/dax memory, as KVM straight up
> doesn't put any references to ZONE_DEVICE pages acquired by gup().
>
> Note, Dan Williams proposed an alternative solution of doing put_page()
> on ZONE_DEVICE pages immediately after gup() in order to simplify the
> auditing needed to ensure is_zone_device_page() is called if and only if
> the backing device is pinned (via gup()). But that approach would break
> kvm_vcpu_{un}map() as KVM requires the page to be pinned from map() 'til
> unmap() when accessing guest memory, unlike KVM's secondary MMU, which
> coordinates with mmu_notifier invalidations to avoid creating stale
> page references, i.e. doesn't rely on pages being pinned.
>
> [*] http://lkml.kernel.org/r/20190919115547.GA17963@angband.pl
>
> Reported-by: Adam Borowski <kilobyte@angband.pl>
> Debugged-by: David Hildenbrand <david@redhat.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
> Cc: stable@vger.kernel.org
Perhaps add:
Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
...since that was the first kernel that broke KVM's assumption about
which pfn types needed to have the reference count managed.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH v2 1/3] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved
2019-11-11 22:39 ` Dan Williams
@ 2019-11-11 22:43 ` Paolo Bonzini
0 siblings, 0 replies; 8+ messages in thread
From: Paolo Bonzini @ 2019-11-11 22:43 UTC (permalink / raw)
To: Dan Williams, Sean Christopherson
Cc: Radim Krčmář,
Vitaly Kuznetsov, Wanpeng Li, Jim Mattson, Joerg Roedel,
KVM list, Linux Kernel Mailing List, Adam Borowski,
David Hildenbrand
On 11/11/19 23:39, Dan Williams wrote:
>> [*] http://lkml.kernel.org/r/20190919115547.GA17963@angband.pl
>>
>> Reported-by: Adam Borowski <kilobyte@angband.pl>
>> Debugged-by: David Hildenbrand <david@redhat.com>
>> Cc: Dan Williams <dan.j.williams@intel.com>
> Acked-by: Dan Williams <dan.j.williams@intel.com>
>
>> Cc: stable@vger.kernel.org
> Perhaps add:
>
> Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
>
> ...since that was the first kernel that broke KVM's assumption about
> which pfn types needed to have the reference count managed.
>
Done, thanks!
Paolo
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH v2 1/3] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved
2019-11-11 22:12 ` [PATCH v2 1/3] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved Sean Christopherson
2019-11-11 22:20 ` Paolo Bonzini
2019-11-11 22:39 ` Dan Williams
@ 2019-11-12 7:06 ` David Hildenbrand
2 siblings, 0 replies; 8+ messages in thread
From: David Hildenbrand @ 2019-11-12 7:06 UTC (permalink / raw)
To: Sean Christopherson
Cc: Paolo Bonzini, Radim Krčmář,
Vitaly Kuznetsov, Wanpeng Li, Jim Mattson, Joerg Roedel, kvm,
linux-kernel, Adam Borowski, David Hildenbrand, Dan Williams
> Am 11.11.2019 um 23:12 schrieb Sean Christopherson <sean.j.christopherson@intel.com>:
>
> Explicitly exempt ZONE_DEVICE pages from kvm_is_reserved_pfn() and
> instead manually handle ZONE_DEVICE on a case-by-case basis. For things
> like page refcounts, KVM needs to treat ZONE_DEVICE pages like normal
> pages, e.g. put pages grabbed via gup(). But for flows such as setting
> A/D bits or shifting refcounts for transparent huge pages, KVM needs to
> to avoid processing ZONE_DEVICE pages as the flows in question lack the
> underlying machinery for proper handling of ZONE_DEVICE pages.
>
> This fixes a hang reported by Adam Borowski[*] in dev_pagemap_cleanup()
> when running a KVM guest backed with /dev/dax memory, as KVM straight up
> doesn't put any references to ZONE_DEVICE pages acquired by gup().
>
> Note, Dan Williams proposed an alternative solution of doing put_page()
> on ZONE_DEVICE pages immediately after gup() in order to simplify the
> auditing needed to ensure is_zone_device_page() is called if and only if
> the backing device is pinned (via gup()). But that approach would break
> kvm_vcpu_{un}map() as KVM requires the page to be pinned from map() 'til
> unmap() when accessing guest memory, unlike KVM's secondary MMU, which
> coordinates with mmu_notifier invalidations to avoid creating stale
> page references, i.e. doesn't rely on pages being pinned.
>
> [*] http://lkml.kernel.org/r/20190919115547.GA17963@angband.pl
>
> Reported-by: Adam Borowski <kilobyte@angband.pl>
> Debugged-by: David Hildenbrand <david@redhat.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> arch/x86/kvm/mmu.c | 8 ++++----
> include/linux/kvm_host.h | 1 +
> virt/kvm/kvm_main.c | 26 +++++++++++++++++++++++---
> 3 files changed, 28 insertions(+), 7 deletions(-)
>
Thanks for taking care of this! Other KVM related code (PPC, vfio) also has a reserved check (see my series), I didn‘t have a look yet at the details, how reserved pages are treated. Will do so in the next weeks, after hollidays.
Acked-by: David Hildenbrand <david@redhat.com>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 24c23c66b226..bf82b1f2e834 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -3306,7 +3306,7 @@ static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu,
> * here.
> */
> if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) &&
> - level == PT_PAGE_TABLE_LEVEL &&
> + !kvm_is_zone_device_pfn(pfn) && level == PT_PAGE_TABLE_LEVEL &&
> PageTransCompoundMap(pfn_to_page(pfn)) &&
> !mmu_gfn_lpage_is_disallowed(vcpu, gfn, PT_DIRECTORY_LEVEL)) {
> unsigned long mask;
> @@ -5914,9 +5914,9 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
> * the guest, and the guest page table is using 4K page size
> * mapping if the indirect sp has level = 1.
> */
> - if (sp->role.direct &&
> - !kvm_is_reserved_pfn(pfn) &&
> - PageTransCompoundMap(pfn_to_page(pfn))) {
> + if (sp->role.direct && !kvm_is_reserved_pfn(pfn) &&
> + !kvm_is_zone_device_pfn(pfn) &&
> + PageTransCompoundMap(pfn_to_page(pfn))) {
> pte_list_remove(rmap_head, sptep);
>
> if (kvm_available_flush_tlb_with_range())
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index a817e446c9aa..4ad1cd7d2d4d 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -966,6 +966,7 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu);
> void kvm_vcpu_kick(struct kvm_vcpu *vcpu);
>
> bool kvm_is_reserved_pfn(kvm_pfn_t pfn);
> +bool kvm_is_zone_device_pfn(kvm_pfn_t pfn);
>
> struct kvm_irq_ack_notifier {
> struct hlist_node link;
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index b8534c6b8cf6..bc9d10a0a334 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -149,10 +149,30 @@ __weak int kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
> return 0;
> }
>
> +bool kvm_is_zone_device_pfn(kvm_pfn_t pfn)
> +{
> + /*
> + * The metadata used by is_zone_device_page() to determine whether or
> + * not a page is ZONE_DEVICE is guaranteed to be valid if and only if
> + * the device has been pinned, e.g. by get_user_pages(). WARN if the
> + * page_count() is zero to help detect bad usage of this helper.
> + */
> + if (!pfn_valid(pfn) || WARN_ON_ONCE(!page_count(pfn_to_page(pfn))))
> + return false;
> +
> + return is_zone_device_page(pfn_to_page(pfn));
> +}
> +
> bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
> {
> + /*
> + * ZONE_DEVICE pages currently set PG_reserved, but from a refcounting
> + * perspective they are "normal" pages, albeit with slightly different
> + * usage rules.
> + */
> if (pfn_valid(pfn))
> - return PageReserved(pfn_to_page(pfn));
> + return PageReserved(pfn_to_page(pfn)) &&
> + !kvm_is_zone_device_pfn(pfn);
>
> return true;
> }
> @@ -1865,7 +1885,7 @@ EXPORT_SYMBOL_GPL(kvm_release_pfn_dirty);
>
> void kvm_set_pfn_dirty(kvm_pfn_t pfn)
> {
> - if (!kvm_is_reserved_pfn(pfn)) {
> + if (!kvm_is_reserved_pfn(pfn) && !kvm_is_zone_device_pfn(pfn)) {
> struct page *page = pfn_to_page(pfn);
>
> SetPageDirty(page);
> @@ -1875,7 +1895,7 @@ EXPORT_SYMBOL_GPL(kvm_set_pfn_dirty);
>
> void kvm_set_pfn_accessed(kvm_pfn_t pfn)
> {
> - if (!kvm_is_reserved_pfn(pfn))
> + if (!kvm_is_reserved_pfn(pfn) && !kvm_is_zone_device_pfn(pfn))
> mark_page_accessed(pfn_to_page(pfn));
> }
> EXPORT_SYMBOL_GPL(kvm_set_pfn_accessed);
> --
> 2.24.0
>
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2019-11-12 7:07 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-11-11 22:12 [PATCH v2 0/3] KVM: MMU: Fix a refcount bug with ZONE_DEVICE pages Sean Christopherson
2019-11-11 22:12 ` [PATCH v2 1/3] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved Sean Christopherson
2019-11-11 22:20 ` Paolo Bonzini
2019-11-11 22:39 ` Dan Williams
2019-11-11 22:43 ` Paolo Bonzini
2019-11-12 7:06 ` David Hildenbrand
2019-11-11 22:12 ` [PATCH v2 2/3] KVM: x86/mmu: Remove superfluous is_error_pfn() check from THP adjust Sean Christopherson
2019-11-11 22:12 ` [PATCH v2 3/3] KVM: x86/mmu: Add helper to consolidate huge page promotion Sean Christopherson
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