diff mbox series

[v7,19/23] KVM: x86/mmu: Zap collapsible SPTEs in shadow MMU at all possible levels

Message ID 20220622192710.2547152-20-pbonzini@redhat.com
State Accepted
Headers show
Series KVM: Extend Eager Page Splitting to the shadow MMU | expand

Commit Message

Paolo Bonzini June 22, 2022, 7:27 p.m. UTC 
From: David Matlack <dmatlack@google.com>

Currently KVM only zaps collapsible 4KiB SPTEs in the shadow MMU. This
is fine for now since KVM never creates intermediate huge pages during
dirty logging. In other words, KVM always replaces 1GiB pages directly
with 4KiB pages, so there is no reason to look for collapsible 2MiB
pages.

However, this will stop being true once the shadow MMU participates in
eager page splitting. During eager page splitting, each 1GiB is first
split into 2MiB pages and then those are split into 4KiB pages. The
intermediate 2MiB pages may be left behind if an error condition causes
eager page splitting to bail early.

No functional change intended.

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220516232138.1783324-20-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/mmu/mmu.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

Comments

Sean Christopherson June 23, 2022, 11:53 p.m. UTC | #1 
On Wed, Jun 22, 2022, Paolo Bonzini wrote:
> From: David Matlack <dmatlack@google.com>
> 
> Currently KVM only zaps collapsible 4KiB SPTEs in the shadow MMU. This
> is fine for now since KVM never creates intermediate huge pages during
> dirty logging. In other words, KVM always replaces 1GiB pages directly
> with 4KiB pages, so there is no reason to look for collapsible 2MiB
> pages.
> 
> However, this will stop being true once the shadow MMU participates in
> eager page splitting. During eager page splitting, each 1GiB is first
> split into 2MiB pages and then those are split into 4KiB pages. The
> intermediate 2MiB pages may be left behind if an error condition causes
> eager page splitting to bail early.
> 
> No functional change intended.
> 
> Reviewed-by: Peter Xu <peterx@redhat.com>
> Signed-off-by: David Matlack <dmatlack@google.com>
> Message-Id: <20220516232138.1783324-20-dmatlack@google.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 13a059ad5dc7..36bc49f08d60 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -6154,18 +6154,25 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
>  	return need_tlb_flush;
>  }
>  
> +static void kvm_rmap_zap_collapsible_sptes(struct kvm *kvm,
> +					   const struct kvm_memory_slot *slot)
> +{
> +	/*
> +	 * Note, use KVM_MAX_HUGEPAGE_LEVEL - 1 since there's no need to zap
> +	 * pages that are already mapped at the maximum possible level.
> +	 */
> +	if (slot_handle_level(kvm, slot, kvm_mmu_zap_collapsible_spte,
> +			      PG_LEVEL_4K, KVM_MAX_HUGEPAGE_LEVEL - 1,
> +			      true))

Can you fix this up to put "true" on the previous line?

And if you do that, maybe also tweak the comment to reference "hugepage level"
instead of "possible level"?

---
 arch/x86/kvm/mmu/mmu.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 8825716060e4..34b0e85b26a4 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -6450,12 +6450,11 @@ static void kvm_rmap_zap_collapsible_sptes(struct kvm *kvm,
 					   const struct kvm_memory_slot *slot)
 {
 	/*
-	 * Note, use KVM_MAX_HUGEPAGE_LEVEL - 1 since there's no need to zap
-	 * pages that are already mapped at the maximum possible level.
+	 * Note, use KVM_MAX_HUGEPAGE_LEVEL - 1, there's no need to zap pages
+	 * that are already mapped at the maximum hugepage level.
 	 */
 	if (slot_handle_level(kvm, slot, kvm_mmu_zap_collapsible_spte,
-			      PG_LEVEL_4K, KVM_MAX_HUGEPAGE_LEVEL - 1,
-			      true))
+			      PG_LEVEL_4K, KVM_MAX_HUGEPAGE_LEVEL - 1, true))
 		kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
 }


base-commit: fd43332c2900db8ca852676f37f0ab423d0c369a
--
diff mbox series

Patch

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 13a059ad5dc7..36bc49f08d60 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -6154,18 +6154,25 @@  static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
 	return need_tlb_flush;
 }
 
+static void kvm_rmap_zap_collapsible_sptes(struct kvm *kvm,
+					   const struct kvm_memory_slot *slot)
+{
+	/*
+	 * Note, use KVM_MAX_HUGEPAGE_LEVEL - 1 since there's no need to zap
+	 * pages that are already mapped at the maximum possible level.
+	 */
+	if (slot_handle_level(kvm, slot, kvm_mmu_zap_collapsible_spte,
+			      PG_LEVEL_4K, KVM_MAX_HUGEPAGE_LEVEL - 1,
+			      true))
+		kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
+}
+
 void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
 				   const struct kvm_memory_slot *slot)
 {
 	if (kvm_memslots_have_rmaps(kvm)) {
 		write_lock(&kvm->mmu_lock);
-		/*
-		 * Zap only 4k SPTEs since the legacy MMU only supports dirty
-		 * logging at a 4k granularity and never creates collapsible
-		 * 2m SPTEs during dirty logging.
-		 */
-		if (slot_handle_level_4k(kvm, slot, kvm_mmu_zap_collapsible_spte, true))
-			kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
+		kvm_rmap_zap_collapsible_sptes(kvm, slot);
 		write_unlock(&kvm->mmu_lock);
 	}