On Fri, 2022-02-18 at 21:00 +0000, Sean Christopherson wrote: > 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; > > Is this actually related to the discussion? The original issue that Paolo found in his patch was that kvm_mmu_update_root now reads _current_ cr3, thus it has to be set before calling it. I do agree that kvm_set_cr3 doesn't need to do anything when TDP is enabled, this is a different issue which doesn't cause much harm (the fast_pgd_switch with direct roots will reuse current root), but still would raise KVM_REQ_LOAD_MMU_PGD without need for it and such. About the patch itself, other than this mentioned issue, it looks fine to me. Best regards, Maxim Levitsky
