Messages in this thread | | | Date | Thu, 9 Dec 2021 23:46:03 +0100 | Subject | Re: [PATCH 17/15] KVM: X86: Ensure pae_root to be reconstructed for shadow paging if the guest PDPTEs is changed | From | Paolo Bonzini <> |
| |
On 12/8/21 01:15, Sean Christopherson wrote: >> @@ -832,8 +832,14 @@ int load_pdptrs(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, unsigned long cr3) >> if (memcmp(mmu->pdptrs, pdpte, sizeof(mmu->pdptrs))) { >> memcpy(mmu->pdptrs, pdpte, sizeof(mmu->pdptrs)); >> kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR); >> - /* Ensure the dirty PDPTEs to be loaded. */ >> - kvm_make_request(KVM_REQ_LOAD_MMU_PGD, vcpu); >> + /* >> + * Ensure the dirty PDPTEs to be loaded for VMX with EPT >> + * enabled or pae_root to be reconstructed for shadow paging. >> + */ >> + if (tdp_enabled) >> + kvm_make_request(KVM_REQ_LOAD_MMU_PGD, vcpu); >> + else >> + kvm_mmu_free_roots(vcpu, vcpu->arch.mmu, KVM_MMU_ROOT_CURRENT); > Shouldn't matter since it's legacy shadow paging, but @mmu should be used instead > of vcpu->arch.mmuvcpu->arch.mmu.
In kvm/next actually there's no mmu parameter to load_pdptrs, so it's okay to keep vcpu->arch.mmu.
> To avoid a dependency on the previous patch, I think it makes sense to have this be: > > if (!tdp_enabled && memcmp(mmu->pdptrs, pdpte, sizeof(mmu->pdptrs))) > kvm_mmu_free_roots(vcpu, mmu, KVM_MMU_ROOT_CURRENT); > > before the memcpy(). > > Then we can decide independently if skipping the KVM_REQ_LOAD_MMU_PGD if the > PDPTRs are unchanged with respect to the MMU is safe.
Do you disagree that there's already an invariant that the PDPTRs can only be dirty if KVM_REQ_LOAD_MMU_PGD---and therefore a previous change to the PDPTRs would have triggered KVM_REQ_LOAD_MMU_PGD? This is opposed to the guest TLB flush due to MOV CR3; that one has to be done unconditionally for PAE paging, and it is handled separately within kvm_set_cr3.
Paolo
| |