[PATCH 06/24] kvm: x86/mmu: Skip no-op changes in TDP MMU functions

Ben Gardon
2021-01-12T18:12:49Z

Skip setting SPTEs if no change is expected.

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

Signed-off-by: Ben Gardon <bgardon@google.com>
---
arch/x86/kvm/mmu/tdp_mmu.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 1987da0da66e..2650fa9fe066 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -882,6 +882,9 @@ static bool wrprot_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
!is_last_spte(iter.old_spte, iter.level))
continue;

+ if (!(iter.old_spte & PT_WRITABLE_MASK))
+ continue;
+
new_spte = iter.old_spte & ~PT_WRITABLE_MASK;

tdp_mmu_set_spte_no_dirty_log(kvm, &iter, new_spte);
@@ -1079,6 +1082,9 @@ static bool set_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
if (!is_shadow_present_pte(iter.old_spte))
continue;

+ if (iter.old_spte & shadow_dirty_mask)
+ continue;
+
new_spte = iter.old_spte | shadow_dirty_mask;

tdp_mmu_set_spte(kvm, &iter, new_spte);
--
2.30.0.284.gd98b1dd5eaa7-goog