diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c index adf211860949..e8bd60156941 100644 --- a/arch/x86/kvm/svm/avic.c +++ b/arch/x86/kvm/svm/avic.c @@ -206,6 +206,35 @@ static void avic_activate_vmcb(struct vcpu_svm *svm) svm_clr_intercept(svm, INTERCEPT_CR8_WRITE); + /* + * Flush the TLB when enabling (x2)AVIC and when transitioning between + * xAVIC and x2AVIC, as the CPU may have inserted a TLB entry for the + * "wrong" mapping. + * + * KVM uses a per-VM "scratch" page to back the APIC memslot, because + * KVM also uses per-VM page tables *and* maintains the page table (NPT + * or shadow page) mappings for said memslot even if one or more vCPUs + * have their local APIC hardware-disabled or are in x2APIC mode, i.e. + * even if one or more vCPUs' APIC MMIO BAR is effectively disabled. + * + * If xAVIC is fully enabled, hardware ignores the physical address in + * KVM's page tables, i.e. in the leaf SPTE for the APIC memslot, and + * instead redirects the access to the AVIC backing page, i.e. to the + * vCPU's virtual APIC page. If xAVIC is not enabled (APIC is either + * hardware-disabled or in x2APIC mode), then guest accesses will use + * the page table mapping verbatim, i.e. will access the per-VM scratch + * page, as normal memory. + * + * In both cases, the CPU is allowed to cache TLB entries for the APIC + * base GPA. So, KVM needs to flush the TLB when enabling xAVIC, as + * accesses need to be redirected to the virtual APIC page, but the TLB + * may contain entries pointing at the scratch page. KVM also needs to + * flush the TLB when enabling x2AVIC, as accesses need to go to the + * scratch page, but the TLB may contain entries tagged as xAVIC, i.e. + * entries pointing to the vCPU's virtual APIC page. + */ + kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, &svm->vcpu); + /* * Note: KVM supports hybrid-AVIC mode, where KVM emulates x2APIC MSR * accesses, while interrupt injection to a running vCPU can be @@ -219,12 +248,6 @@ static void avic_activate_vmcb(struct vcpu_svm *svm) /* Disabling MSR intercept for x2APIC registers */ avic_set_x2apic_msr_interception(svm, false); } else { - /* - * Flush the TLB, the guest may have inserted a non-APIC - * mapping into the TLB while AVIC was disabled. - */ - kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, &svm->vcpu); - /* Enabling MSR intercept for x2APIC registers */ avic_set_x2apic_msr_interception(svm, true); }