Now that TLB flushes are properly handled and tracked for L1 vs L2 ASIDs, allocate a separate new ASID for L2 for each vCPU, similar to how VMX handles VPIDs. Drop the unconditional flushes and syncs on nested transitions. Initialize last_asid to 0, such that the L2 ASID is always flushed on first nested VM-Enter after it's allocated. On a Turin CPU, this results in 8-15% performance boost in CPUID rate microbenchmark [1] and netperf TCP_RR latency/throughput. [1]https://lore.kernel.org/kvm/20231109180646.2963718-1-khorenko@virtuozzo.com/ Signed-off-by: Yosry Ahmed --- arch/x86/kvm/svm/nested.c | 28 ++++++++++++++++++++-------- 1 file changed, 20 insertions(+), 8 deletions(-) diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index 9ea8f21be9940..659e9da43945a 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -707,6 +707,10 @@ static void nested_svm_entry_tlb_flush(struct kvm_vcpu *vcpu) * context is not tagged by the ASID, so the shadow NPTs cannot be * reused across different L2 ASIDs. * + * Note, last_asid is initialized as 0, so the first nested VM-Enter + * after setting EFER.SVME will always flush the TLB to avoid using + * stale entries. + * * If L1 requested a full TLB flush for all ASIDs (including its own), * L1's own ASID is also flushed on nested VM-Exit, before running L1. * @@ -727,10 +731,6 @@ static void nested_svm_entry_tlb_flush(struct kvm_vcpu *vcpu) WARN_ON_ONCE(svm->asid != fallback_asid && !is_sev_guest(vcpu)); kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu); } - - /* TODO: optimize unconditional TLB flush/MMU sync */ - kvm_make_request(KVM_REQ_MMU_SYNC, vcpu); - kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu); } static void nested_svm_exit_tlb_flush(struct kvm_vcpu *vcpu) @@ -745,9 +745,6 @@ static void nested_svm_exit_tlb_flush(struct kvm_vcpu *vcpu) if (svm->asid == svm->nested.asid02) kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu); - - kvm_make_request(KVM_REQ_MMU_SYNC, vcpu); - kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu); } /* @@ -1554,7 +1551,20 @@ int svm_allocate_nested(struct vcpu_svm *svm) svm->nested.vmcb02.ptr = page_address(vmcb02_page); svm->nested.vmcb02.pa = __sme_set(page_to_pfn(vmcb02_page) << PAGE_SHIFT); - svm->nested.asid02 = svm->asid; + svm->nested.asid02 = allocate_asid(&svm->vcpu); + + /* + * KVM uses a fallback ASID when out of ASIDs, and fails vCPU creation + * if there's no fallback ASID. ASID allocation must succeed here. + */ + KVM_BUG_ON(!svm->nested.asid02, svm->vcpu.kvm); + + /* + * Clear last_asid to ensure that the ASID is flushed on the first + * nested VM-Enter. Otherwise, stale TLB entries from a previous life of + * the VPID (e.g. different vCPU or even different VM) could be used. + */ + svm->nested.last_asid = 0; return 0; @@ -1571,6 +1581,8 @@ void svm_free_nested(struct vcpu_svm *svm) if (WARN_ON_ONCE(svm->vmcb != svm->vmcb01.ptr)) svm_switch_vmcb(svm, &svm->vmcb01); + free_asid(&svm->vcpu, svm->nested.asid02); + svm_vcpu_free_msrpm(svm->nested.msrpm); svm->nested.msrpm = NULL; -- 2.55.0.229.g6434b31f56-goog