On 10/03/21 23:24, Ben Gardon wrote:
On Wed, Mar 10, 2021 at 1:14 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
On Wed, Mar 10, 2021, Paolo Bonzini wrote:
On 10/03/21 01:30, Sean Christopherson wrote:
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 50ef757c5586..f0c99fa04ef2 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -323,7 +323,18 @@ static void handle_removed_tdp_mmu_page(struct kvm *kvm, u64 *pt,
cpu_relax();
}
} else {
+ /*
+ * If the SPTE is not MMU-present, there is no backing
+ * page associated with the SPTE and so no side effects
+ * that need to be recorded, and exclusive ownership of
+ * mmu_lock ensures the SPTE can't be made present.
+ * Note, zapping MMIO SPTEs is also unnecessary as they
+ * are guarded by the memslots generation, not by being
+ * unreachable.
+ */
old_child_spte = READ_ONCE(*sptep);
+ if (!is_shadow_present_pte(old_child_spte))
+ continue;
/*
* Marking the SPTE as a removed SPTE is not
This optimization also makes me think we could also skip the
__handle_changed_spte call in the read mode case if the SPTE change
was !PRESENT -> REMOVED.
Yes, I think so. It should be a separate patch anyway, so I've queued
this one.
Paolo
