[PATCH v2 26/32] KVM: nVMX: Selectively use TLB_FLUSH_CURRENT for nested VM-Enter/VM-Exit

[Sean Christopherson]

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@xxxxxxxxx>
---
 arch/x86/kvm/vmx/nested.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 19600d4b3344..04cdf7ded1d3 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -1167,16 +1167,19 @@ 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
 	 * redundant flushes further down the nested pipeline.
 	 */
-	if (enable_vpid &&
-	    (!nested_cpu_has_vpid(vmcs12) || !nested_has_guest_tlb_tag(vcpu)))
-		kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
+	if (enable_vpid) {
+		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);
+	}
 }
 
 static bool is_bitwise_subset(u64 superset, u64 subset, u64 mask)
-- 
2.24.1