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Wed, 14 Aug 2024 10:57:59 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGSCwDwNXwiqgNc8qTmHDkSdNy4unKmAQEh5uyse96W8/CeXQ9UmxrPFPRv7DJnqCF/7Y7tMQ== X-Received: by 2002:a05:600c:1da6:b0:426:5471:156a with SMTP id 5b1f17b1804b1-429dd23b7b8mr28648565e9.13.1723658279229; Wed, 14 Aug 2024 10:57:59 -0700 (PDT) Received: from [192.168.10.47] ([151.95.101.29]) by smtp.googlemail.com with ESMTPSA id 5b1f17b1804b1-429ded71ee3sm26570925e9.29.2024.08.14.10.57.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 14 Aug 2024 10:57:58 -0700 (PDT) Message-ID: <5f8c0ca4-ae99-4d1c-8525-51c6f1096eaa@redhat.com> Date: Wed, 14 Aug 2024 19:57:57 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 22/22] KVM: x86/mmu: Detect if unprotect will do anything based on invalid_list To: Sean Christopherson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Gonda , Michael Roth , Vishal Annapurve , Ackerly Tng References: <20240809190319.1710470-1-seanjc@google.com> <20240809190319.1710470-23-seanjc@google.com> From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 8/9/24 21:03, Sean Christopherson wrote: > Explicitly query the list of to-be-zapped shadow pages when checking to > see if unprotecting a gfn for retry has succeeded, i.e. if KVM should > retry the faulting instruction. > > Add a comment to explain why the list needs to be checked before zapping, > which is the primary motivation for this change. > > No functional change intended. > > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/mmu/mmu.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 300a47801685..50695eb2ee22 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -2731,12 +2731,15 @@ bool __kvm_mmu_unprotect_gfn_and_retry(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, > goto out; > } > > - r = false; > write_lock(&kvm->mmu_lock); > - for_each_gfn_valid_sp_with_gptes(kvm, sp, gpa_to_gfn(gpa)) { > - r = true; > + for_each_gfn_valid_sp_with_gptes(kvm, sp, gpa_to_gfn(gpa)) > kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list); > - } > + > + /* > + * Snapshot the result before zapping, as zapping will remove all list > + * entries, i.e. checking the list later would yield a false negative. > + */ Hmm, the comment is kinda overkill? Maybe just /* Return whether there were sptes to zap. */ r = !list_empty(&invalid_test); I'm not sure about patch 21 - I like the simple kvm_mmu_unprotect_page() function. Maybe rename it to kvm_mmu_zap_gfn() and make it static in the same patch? Either way, this small cleanup applies even if the function is not inlined. Thanks, Paolo > + r = !list_empty(&invalid_list); > kvm_mmu_commit_zap_page(kvm, &invalid_list); > write_unlock(&kvm->mmu_lock); >