This is a note to let you know that I've just added the patch titled KVM: x86/mmu: Expand on the comment in kvm_vcpu_ad_need_write_protect() to the 5.11-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-x86-mmu-expand-on-the-comment-in-kvm_vcpu_ad_nee.patch and it can be found in the queue-5.11 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit a4d2c639de2fbf92345a35a8e411a103bdcf71d8 Author: Sean Christopherson <seanjc@xxxxxxxxxx> Date: Fri Feb 12 16:50:08 2021 -0800 KVM: x86/mmu: Expand on the comment in kvm_vcpu_ad_need_write_protect() [ Upstream commit 2855f98265dc579bd2becb79ce0156d08e0df813 ] 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@xxxxxxxxxx> Message-Id: <20210213005015.1651772-8-seanjc@xxxxxxxxxx> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h index bfc6389edc28..8404145fb179 100644 --- a/arch/x86/kvm/mmu/mmu_internal.h +++ b/arch/x86/kvm/mmu/mmu_internal.h @@ -79,7 +79,10 @@ 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; }