[PATCH 07/14] KVM: x86/mmu: Expand on the comment in kvm_vcpu_ad_need_write_protect()

Sean Christopherson
2021-02-13T00:53:21Z

Expand the comment about need to use write-protection for nested EPT
when PML is enabled to clarify that the tagging is a nop when PML is
_not_ enabled. Without the clarification, omitting the PML check looks
wrong at first^Wfifth glance.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/mmu/mmu_internal.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 0b55aa561ec8..72b0928f2b2d 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -84,7 +84,10 @@ static inline bool kvm_vcpu_ad_need_write_protect(struct kvm_vcpu *vcpu)
* When using the EPT page-modification log, the GPAs in the log
* would come from L2 rather than L1. Therefore, we need to rely
* on write protection to record dirty pages. This also bypasses
- * PML, since writes now result in a vmexit.
+ * PML, since writes now result in a vmexit. Note, this helper will
+ * tag SPTEs as needing write-protection even if PML is disabled or
+ * unsupported, but that's ok because the tag is consumed if and only
+ * if PML is enabled. Omit the PML check to save a few uops.
*/
return vcpu->arch.mmu == &vcpu->arch.guest_mmu;
}
--
2.30.0.478.g8a0d178c01-goog