[v2,4/5] KVM: nVMX: Fix conditions for interrupt injection

Commit Message

Jan Kiszka March 16, 2013, 10:23 a.m. UTC

From: Jan Kiszka <[e-mail]>

If we are in guest mode, L0 can only inject events into L2 if L1 has
nothing pending. Otherwise, L0 would overwrite L1's events and they
would get lost. But even if no injection of L1 is pending, we do not
want L0 to interrupt unnecessarily an on going vmentry with all its side
effects on the vmcs. Therefore, injection shall be disallowed during
L1->L2 transitions. This check is conceptually independent of
nested_exit_on_intr.

If L1 traps external interrupts, then we also need to look at L1's
idt_vectoring_info_field. If it is empty, we can kick the guest from L2
to L1, just like the previous code worked.

Signed-off-by: Jan Kiszka <[e-mail]>
---
 arch/x86/kvm/vmx.c |   28 ++++++++++++++++++++--------
 1 files changed, 20 insertions(+), 8 deletions(-)

Patch

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index a5f56df..27e7e59 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4324,16 +4324,28 @@  static int vmx_nmi_allowed(struct kvm_vcpu *vcpu)
 
 static int vmx_interrupt_allowed(struct kvm_vcpu *vcpu)
 {
-	if (is_guest_mode(vcpu) && nested_exit_on_intr(vcpu)) {
+	if (is_guest_mode(vcpu)) {
 		struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
-		if (to_vmx(vcpu)->nested.nested_run_pending ||
-		    (vmcs12->idt_vectoring_info_field &
-		     VECTORING_INFO_VALID_MASK))
+
+		if (to_vmx(vcpu)->nested.nested_run_pending)
 			return 0;
-		nested_vmx_vmexit(vcpu);
-		vmcs12->vm_exit_reason = EXIT_REASON_EXTERNAL_INTERRUPT;
-		vmcs12->vm_exit_intr_info = 0;
-		/* fall through to normal code, but now in L1, not L2 */
+		if (nested_exit_on_intr(vcpu)) {
+			/*
+			 * Check if the idt_vectoring_info_field is free. We
+			 * cannot raise EXIT_REASON_EXTERNAL_INTERRUPT if it
+			 * isn't.
+			 */
+			if (vmcs12->idt_vectoring_info_field &
+			    VECTORING_INFO_VALID_MASK)
+				return 0;
+			nested_vmx_vmexit(vcpu);
+			vmcs12->vm_exit_reason =
+				EXIT_REASON_EXTERNAL_INTERRUPT;
+			vmcs12->vm_exit_intr_info = 0;
+			/*
+			 * fall through to normal code, but now in L1, not L2
+			 */
+		}
 	}
 
 	return (vmcs_readl(GUEST_RFLAGS) & X86_EFLAGS_IF) &&