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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id y23sm3840220pfa.67.2022.02.18.13.00.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Feb 2022 13:00:14 -0800 (PST) Date: Fri, 18 Feb 2022 21:00:10 +0000 From: Sean Christopherson To: Paolo Bonzini Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v2 15/18] KVM: x86/mmu: rename kvm_mmu_new_pgd, introduce variant that calls get_guest_pgd Message-ID: References: <20220217210340.312449-1-pbonzini@redhat.com> <20220217210340.312449-16-pbonzini@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 18, 2022, Paolo Bonzini wrote: > On 2/17/22 22:03, Paolo Bonzini wrote: > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > index adcee7c305ca..9800c8883a48 100644 > > --- a/arch/x86/kvm/x86.c > > +++ b/arch/x86/kvm/x86.c > > @@ -1189,7 +1189,7 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3) > > return 1; > > if (cr3 != kvm_read_cr3(vcpu)) > > - kvm_mmu_new_pgd(vcpu, cr3); > > + kvm_mmu_update_root(vcpu); > > vcpu->arch.cr3 = cr3; > > kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3); > > Uh-oh, this has to become: > > vcpu->arch.cr3 = cr3; > kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3); > if (!is_pae_paging(vcpu)) > kvm_mmu_update_root(vcpu); > > The regression would go away after patch 16, but this is more tidy apart > from having to check is_pae_paging *again*. > > Incremental patch: > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index adcee7c305ca..0085e9fba372 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -1188,11 +1189,11 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3) > if (is_pae_paging(vcpu) && !load_pdptrs(vcpu, cr3)) > return 1; > - if (cr3 != kvm_read_cr3(vcpu)) > - kvm_mmu_update_root(vcpu); > - > vcpu->arch.cr3 = cr3; > kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3); > + if (!is_pae_paging(vcpu)) > + kvm_mmu_update_root(vcpu); > + > /* Do not call post_set_cr3, we do not get here for confidential guests. */ > > An alternative is to move the vcpu->arch.cr3 update in load_pdptrs. > Reviewers, let me know if you prefer that, then I'll send v3. c) None of the above. MOV CR3 never requires a new root if TDP is enabled, and the guest_mmu is used if and only if TDP is enabled. Even when KVM intercepts CR3 when EPT=1 && URG=0, it does so only to snapshot vcpu->arch.cr3, there's no need to get a new PGD. Unless I'm missing something, your original suggestion of checking tdp_enabled is the way to go. diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 6e0f7f22c6a7..2b02029c63d0 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1187,7 +1187,7 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3) if (is_pae_paging(vcpu) && !load_pdptrs(vcpu, cr3)) return 1; - if (cr3 != kvm_read_cr3(vcpu)) + if (!tdp_enabled && cr3 != kvm_read_cr3(vcpu)) kvm_mmu_new_pgd(vcpu, cr3); vcpu->arch.cr3 = cr3;