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KVM: x86/mmu: Expand on the comment in kvm_vcpu_ad_need_write_protect() 

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>
Message-Id: <20210213005015.1651772-8-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-02-12 16:50:08 -08:00 committed by Paolo Bonzini
parent c3bb9a2083
commit 2855f98265
1 changed files with 4 additions and 1 deletions
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5
arch/x86/kvm/mmu/mmu_internal.h
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@ -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;
}