KVM: nVMX: Selectively use TLB_FLUSH_CURRENT for nested VM-Enter/VM-Exit

Flush only the current context, as opposed to all contexts, when
requesting a TLB flush to handle the scenario where a L1 does not expect
a TLB flush, but one is required because L1 and L2 shared an ASID.  This
occurs if EPT is disabled (no per-EPTP tag), VPID is enabled (hardware
doesn't flush unconditionally) and vmcs02 does not have its own VPID due
to exhaustion of available VPIDs.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200320212833.3507-27-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 567a7a0..deddf0f 100644 (file)
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -1152,8 +1152,8 @@ static void nested_vmx_transition_tlb_flush(struct kvm_vcpu *vcpu,
         *
         * If VPID is enabled and used by vmc12, but L2 does not have a unique
         * TLB tag (ASID), i.e. EPT is disabled and KVM was unable to allocate
-        * a VPID for L2, flush the TLB as the effective ASID is common to both
-        * L1 and L2.
+        * a VPID for L2, flush the current context as the effective ASID is
+        * common to both L1 and L2.
         *
         * Defer the flush so that it runs after vmcs02.EPTP has been set by
         * KVM_REQ_LOAD_MMU_PGD (if nested EPT is enabled) and to avoid
@@ -1165,8 +1165,10 @@ static void nested_vmx_transition_tlb_flush(struct kvm_vcpu *vcpu,
         * mapping between vpid02 and vpid12, vpid02 is per-vCPU and reused for
         * all nested vCPUs.
         */
-       if (!nested_cpu_has_vpid(vmcs12) || !nested_has_guest_tlb_tag(vcpu)) {
+       if (!nested_cpu_has_vpid(vmcs12)) {
                kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
+       } else if (!nested_has_guest_tlb_tag(vcpu)) {
+               kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
        } else if (is_vmenter &&
                   vmcs12->virtual_processor_id != vmx->nested.last_vpid) {
                vmx->nested.last_vpid = vmcs12->virtual_processor_id;