[PATCH v3 21/37] KVM: SVM: Document the ASID logic in svm_flush_tlb()

[Sean Christopherson]

Add a comment in svm_flush_tlb() to document why it flushes only the
current ASID, even when it is invoked when flushing remote TLBs.

Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
 arch/x86/kvm/svm.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index dfa3b53f8437..8c3700b44eb4 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5630,6 +5630,13 @@ static void svm_flush_tlb(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
+	/*
+	 * Flush only the current ASID even if the TLB flush was invoked via
+	 * kvm_flush_remote_tlbs().  Although flushing remote TLBs requires all
+	 * ASIDs to be flushed, KVM uses a single ASID for L1 and L2, and
+	 * unconditionally does a TLB flush on both nested VM-Enter and nested
+	 * VM-Exit (via kvm_mmu_reset_context()).
+	 */
 	if (static_cpu_has(X86_FEATURE_FLUSHBYASID))
 		svm->vmcb->control.tlb_ctl = TLB_CONTROL_FLUSH_ASID;
 	else
-- 
2.24.1