[PATCH v4 08/13] KVM: x86/mmu: Clear only A-bit (if enabled) when aging TDP MMU SPTEs

[Sean Christopherson]

From: Vipin Sharma <vipinsh@xxxxxxxxxx>

Use tdp_mmu_clear_spte_bits() when clearing the Accessed bit in TDP MMU
SPTEs so as to use an atomic-AND instead of XCHG to clear the A-bit.
Similar to the D-bit story, this will allow KVM to bypass
__handle_changed_spte() by ensuring only the A-bit is modified.

Link: https://lore.kernel.org/all/Y9HcHRBShQgjxsQb@xxxxxxxxxx
Signed-off-by: Vipin Sharma <vipinsh@xxxxxxxxxx>
Reviewed-by: David Matlack <dmatlack@xxxxxxxxxx>
[sean: massage changelog]
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 38 +++++++++++++++++++++-----------------
 1 file changed, 21 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 3cc81fa22b7f..adbdfed287cc 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -756,13 +756,6 @@ static inline void tdp_mmu_set_spte(struct kvm *kvm, struct tdp_iter *iter,
 	_tdp_mmu_set_spte(kvm, iter, new_spte, true);
 }
 
-static inline void tdp_mmu_set_spte_no_acc_track(struct kvm *kvm,
-						 struct tdp_iter *iter,
-						 u64 new_spte)
-{
-	_tdp_mmu_set_spte(kvm, iter, new_spte, false);
-}
-
 #define tdp_root_for_each_pte(_iter, _root, _start, _end) \
 	for_each_tdp_pte(_iter, _root, _start, _end)
 
@@ -1248,33 +1241,44 @@ static __always_inline bool kvm_tdp_mmu_handle_gfn(struct kvm *kvm,
 /*
  * Mark the SPTEs range of GFNs [start, end) unaccessed and return non-zero
  * if any of the GFNs in the range have been accessed.
+ *
+ * No need to mark the corresponding PFN as accessed as this call is coming
+ * from the clear_young() or clear_flush_young() notifier, which uses the
+ * return value to determine if the page has been accessed.
  */
 static bool age_gfn_range(struct kvm *kvm, struct tdp_iter *iter,
 			  struct kvm_gfn_range *range)
 {
-	u64 new_spte = 0;
+	u64 new_spte;
 
 	/* If we have a non-accessed entry we don't need to change the pte. */
 	if (!is_accessed_spte(iter->old_spte))
 		return false;
 
-	new_spte = iter->old_spte;
-
-	if (spte_ad_enabled(new_spte)) {
-		new_spte &= ~shadow_accessed_mask;
+	if (spte_ad_enabled(iter->old_spte)) {
+		iter->old_spte = tdp_mmu_clear_spte_bits(iter->sptep,
+							 iter->old_spte,
+							 shadow_accessed_mask,
+							 iter->level);
+		new_spte = iter->old_spte & ~shadow_accessed_mask;
 	} else {
 		/*
 		 * Capture the dirty status of the page, so that it doesn't get
 		 * lost when the SPTE is marked for access tracking.
 		 */
-		if (is_writable_pte(new_spte))
-			kvm_set_pfn_dirty(spte_to_pfn(new_spte));
+		if (is_writable_pte(iter->old_spte))
+			kvm_set_pfn_dirty(spte_to_pfn(iter->old_spte));
 
-		new_spte = mark_spte_for_access_track(new_spte);
+		new_spte = mark_spte_for_access_track(iter->old_spte);
+		iter->old_spte = kvm_tdp_mmu_write_spte(iter->sptep,
+							iter->old_spte, new_spte,
+							iter->level);
 	}
 
-	tdp_mmu_set_spte_no_acc_track(kvm, iter, new_spte);
-
+	__handle_changed_spte(kvm, iter->as_id, iter->gfn, iter->old_spte,
+			      new_spte, iter->level, false);
+	handle_changed_spte_dirty_log(kvm, iter->as_id, iter->gfn,
+				      iter->old_spte, new_spte, iter->level);
 	return true;
 }
 
-- 
2.40.0.rc2.332.ga46443480c-goog