[10/24] kvm: x86/mmu: Factor out handle disconnected pt
diff mbox series

Message ID 20210112181041.356734-11-bgardon@google.com
State New, archived
Headers show
Series
  • Allow parallel page faults with TDP MMU
Related show

Commit Message

Ben Gardon Jan. 12, 2021, 6:10 p.m. UTC
Factor out the code to handle a disconnected subtree of the TDP paging
structure from the code to handle the change to an individual SPTE.
Future commits will build on this to allow asynchronous page freeing.

No functional change intended.

Reviewed-by: Peter Feiner <pfeiner@google.com>

Signed-off-by: Ben Gardon <bgardon@google.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 75 +++++++++++++++++++++++---------------
 1 file changed, 46 insertions(+), 29 deletions(-)

Comments

Sean Christopherson Jan. 20, 2021, 8:30 p.m. UTC | #1
Spell out "page tables"?  Not short on chars.  The grammar is also a bit funky.

  KVM: x86/mmu: Factor out handling of disconnected page tables

On Tue, Jan 12, 2021, Ben Gardon wrote:
> Factor out the code to handle a disconnected subtree of the TDP paging
> structure from the code to handle the change to an individual SPTE.
> Future commits will build on this to allow asynchronous page freeing.
> 
> No functional change intended.
> 
> Reviewed-by: Peter Feiner <pfeiner@google.com>
> 
> Signed-off-by: Ben Gardon <bgardon@google.com>
> ---
>  arch/x86/kvm/mmu/tdp_mmu.c | 75 +++++++++++++++++++++++---------------
>  1 file changed, 46 insertions(+), 29 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 55df596696c7..e8f35cd46b4c 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -234,6 +234,49 @@ static void handle_changed_spte_dirty_log(struct kvm *kvm, int as_id, gfn_t gfn,
>  	}
>  }
>  
> +/**
> + * handle_disconnected_tdp_mmu_page - handle a pt removed from the TDP structure

Maybe s/disconnected/removed?

I completely understand why you used "disconnected", and to a large extent I
agree it's a good descriptor, but all of the surrounding comments talk about the
page tables being "removed".  And for me, "disconnected" implies that that it
could be reconnected in the future, whereas "removed" is a more firm "this page,
in its current form, is gone for good".

> + *
> + * @kvm: kvm instance
> + * @pt: the page removed from the paging structure
> + *
> + * Given a page table that has been removed from the TDP paging structure,
> + * iterates through the page table to clear SPTEs and free child page tables.
> + */
> +static void handle_disconnected_tdp_mmu_page(struct kvm *kvm, u64 *pt)
> +{
> +	struct kvm_mmu_page *sp;
> +	gfn_t gfn;
> +	int level;
> +	u64 old_child_spte;
> +	int i;

Nit: use reverse fir tree?  I don't think KVM needs to be as strict as tip for
that rule/guideline, but I do think it's usually a net positive for readability.

> +	sp = sptep_to_sp(pt);
> +	gfn = sp->gfn;
> +	level = sp->role.level;

Initialize these from the get-go?  That would held the reader understand these
are local snapshots to shorten lines, as opposed to scratch variables.

	struct kvm_mmu_page *sp = sptep_to_sp(pt);
	int level = sp->role.level;
	gfn_t gfn = sp->gfn;
	u64 old_child_spte;
	int i;

> +
> +	trace_kvm_mmu_prepare_zap_page(sp);
> +
> +	list_del(&sp->link);
> +
> +	if (sp->lpage_disallowed)
> +		unaccount_huge_nx_page(kvm, sp);
> +
> +	for (i = 0; i < PT64_ENT_PER_PAGE; i++) {
> +		old_child_spte = READ_ONCE(*(pt + i));
> +		WRITE_ONCE(*(pt + i), 0);
> +		handle_changed_spte(kvm, kvm_mmu_page_as_id(sp),
> +			gfn + (i * KVM_PAGES_PER_HPAGE(level - 1)),
> +			old_child_spte, 0, level - 1);
> +	}
> +
> +	kvm_flush_remote_tlbs_with_address(kvm, gfn,
> +					   KVM_PAGES_PER_HPAGE(level));
> +
> +	free_page((unsigned long)pt);
> +	kmem_cache_free(mmu_page_header_cache, sp);
> +}
Paolo Bonzini Jan. 26, 2021, 2:14 p.m. UTC | #2
On 12/01/21 19:10, Ben Gardon wrote:
> Factor out the code to handle a disconnected subtree of the TDP paging
> structure from the code to handle the change to an individual SPTE.
> Future commits will build on this to allow asynchronous page freeing.
> 
> No functional change intended.
> 
> Reviewed-by: Peter Feiner <pfeiner@google.com>
> 
> Signed-off-by: Ben Gardon <bgardon@google.com>
> ---
>   arch/x86/kvm/mmu/tdp_mmu.c | 75 +++++++++++++++++++++++---------------
>   1 file changed, 46 insertions(+), 29 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 55df596696c7..e8f35cd46b4c 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -234,6 +234,49 @@ static void handle_changed_spte_dirty_log(struct kvm *kvm, int as_id, gfn_t gfn,
>   	}
>   }
>   
> +/**
> + * handle_disconnected_tdp_mmu_page - handle a pt removed from the TDP structure
> + *
> + * @kvm: kvm instance
> + * @pt: the page removed from the paging structure
> + *
> + * Given a page table that has been removed from the TDP paging structure,
> + * iterates through the page table to clear SPTEs and free child page tables.
> + */
> +static void handle_disconnected_tdp_mmu_page(struct kvm *kvm, u64 *pt)
> +{
> +	struct kvm_mmu_page *sp;
> +	gfn_t gfn;
> +	int level;
> +	u64 old_child_spte;
> +	int i;
> +
> +	sp = sptep_to_sp(pt);
> +	gfn = sp->gfn;
> +	level = sp->role.level;
> +
> +	trace_kvm_mmu_prepare_zap_page(sp);
> +
> +	list_del(&sp->link);
> +
> +	if (sp->lpage_disallowed)
> +		unaccount_huge_nx_page(kvm, sp);
> +
> +	for (i = 0; i < PT64_ENT_PER_PAGE; i++) {
> +		old_child_spte = READ_ONCE(*(pt + i));
> +		WRITE_ONCE(*(pt + i), 0);
> +		handle_changed_spte(kvm, kvm_mmu_page_as_id(sp),
> +			gfn + (i * KVM_PAGES_PER_HPAGE(level - 1)),
> +			old_child_spte, 0, level - 1);
> +	}
> +
> +	kvm_flush_remote_tlbs_with_address(kvm, gfn,
> +					   KVM_PAGES_PER_HPAGE(level));
> +
> +	free_page((unsigned long)pt);
> +	kmem_cache_free(mmu_page_header_cache, sp);
> +}
> +
>   /**
>    * handle_changed_spte - handle bookkeeping associated with an SPTE change
>    * @kvm: kvm instance
> @@ -254,10 +297,6 @@ static void __handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
>   	bool was_leaf = was_present && is_last_spte(old_spte, level);
>   	bool is_leaf = is_present && is_last_spte(new_spte, level);
>   	bool pfn_changed = spte_to_pfn(old_spte) != spte_to_pfn(new_spte);
> -	u64 *pt;
> -	struct kvm_mmu_page *sp;
> -	u64 old_child_spte;
> -	int i;
>   
>   	WARN_ON(level > PT64_ROOT_MAX_LEVEL);
>   	WARN_ON(level < PG_LEVEL_4K);
> @@ -321,31 +360,9 @@ static void __handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
>   	 * Recursively handle child PTs if the change removed a subtree from
>   	 * the paging structure.
>   	 */
> -	if (was_present && !was_leaf && (pfn_changed || !is_present)) {
> -		pt = spte_to_child_pt(old_spte, level);
> -		sp = sptep_to_sp(pt);
> -
> -		trace_kvm_mmu_prepare_zap_page(sp);
> -
> -		list_del(&sp->link);
> -
> -		if (sp->lpage_disallowed)
> -			unaccount_huge_nx_page(kvm, sp);
> -
> -		for (i = 0; i < PT64_ENT_PER_PAGE; i++) {
> -			old_child_spte = READ_ONCE(*(pt + i));
> -			WRITE_ONCE(*(pt + i), 0);
> -			handle_changed_spte(kvm, as_id,
> -				gfn + (i * KVM_PAGES_PER_HPAGE(level - 1)),
> -				old_child_spte, 0, level - 1);
> -		}
> -
> -		kvm_flush_remote_tlbs_with_address(kvm, gfn,
> -						   KVM_PAGES_PER_HPAGE(level));
> -
> -		free_page((unsigned long)pt);
> -		kmem_cache_free(mmu_page_header_cache, sp);
> -	}
> +	if (was_present && !was_leaf && (pfn_changed || !is_present))
> +		handle_disconnected_tdp_mmu_page(kvm,
> +				spte_to_child_pt(old_spte, level));
>   }
>   
>   static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
> 

Queued, thanks.

Paolo

Patch
diff mbox series

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 55df596696c7..e8f35cd46b4c 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -234,6 +234,49 @@  static void handle_changed_spte_dirty_log(struct kvm *kvm, int as_id, gfn_t gfn,
 	}
 }
 
+/**
+ * handle_disconnected_tdp_mmu_page - handle a pt removed from the TDP structure
+ *
+ * @kvm: kvm instance
+ * @pt: the page removed from the paging structure
+ *
+ * Given a page table that has been removed from the TDP paging structure,
+ * iterates through the page table to clear SPTEs and free child page tables.
+ */
+static void handle_disconnected_tdp_mmu_page(struct kvm *kvm, u64 *pt)
+{
+	struct kvm_mmu_page *sp;
+	gfn_t gfn;
+	int level;
+	u64 old_child_spte;
+	int i;
+
+	sp = sptep_to_sp(pt);
+	gfn = sp->gfn;
+	level = sp->role.level;
+
+	trace_kvm_mmu_prepare_zap_page(sp);
+
+	list_del(&sp->link);
+
+	if (sp->lpage_disallowed)
+		unaccount_huge_nx_page(kvm, sp);
+
+	for (i = 0; i < PT64_ENT_PER_PAGE; i++) {
+		old_child_spte = READ_ONCE(*(pt + i));
+		WRITE_ONCE(*(pt + i), 0);
+		handle_changed_spte(kvm, kvm_mmu_page_as_id(sp),
+			gfn + (i * KVM_PAGES_PER_HPAGE(level - 1)),
+			old_child_spte, 0, level - 1);
+	}
+
+	kvm_flush_remote_tlbs_with_address(kvm, gfn,
+					   KVM_PAGES_PER_HPAGE(level));
+
+	free_page((unsigned long)pt);
+	kmem_cache_free(mmu_page_header_cache, sp);
+}
+
 /**
  * handle_changed_spte - handle bookkeeping associated with an SPTE change
  * @kvm: kvm instance
@@ -254,10 +297,6 @@  static void __handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
 	bool was_leaf = was_present && is_last_spte(old_spte, level);
 	bool is_leaf = is_present && is_last_spte(new_spte, level);
 	bool pfn_changed = spte_to_pfn(old_spte) != spte_to_pfn(new_spte);
-	u64 *pt;
-	struct kvm_mmu_page *sp;
-	u64 old_child_spte;
-	int i;
 
 	WARN_ON(level > PT64_ROOT_MAX_LEVEL);
 	WARN_ON(level < PG_LEVEL_4K);
@@ -321,31 +360,9 @@  static void __handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
 	 * Recursively handle child PTs if the change removed a subtree from
 	 * the paging structure.
 	 */
-	if (was_present && !was_leaf && (pfn_changed || !is_present)) {
-		pt = spte_to_child_pt(old_spte, level);
-		sp = sptep_to_sp(pt);
-
-		trace_kvm_mmu_prepare_zap_page(sp);
-
-		list_del(&sp->link);
-
-		if (sp->lpage_disallowed)
-			unaccount_huge_nx_page(kvm, sp);
-
-		for (i = 0; i < PT64_ENT_PER_PAGE; i++) {
-			old_child_spte = READ_ONCE(*(pt + i));
-			WRITE_ONCE(*(pt + i), 0);
-			handle_changed_spte(kvm, as_id,
-				gfn + (i * KVM_PAGES_PER_HPAGE(level - 1)),
-				old_child_spte, 0, level - 1);
-		}
-
-		kvm_flush_remote_tlbs_with_address(kvm, gfn,
-						   KVM_PAGES_PER_HPAGE(level));
-
-		free_page((unsigned long)pt);
-		kmem_cache_free(mmu_page_header_cache, sp);
-	}
+	if (was_present && !was_leaf && (pfn_changed || !is_present))
+		handle_disconnected_tdp_mmu_page(kvm,
+				spte_to_child_pt(old_spte, level));
 }
 
 static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,