[PATCH 2/2] kvm: nVMX: Single-step traps trump expired VMX-preemption timer

[Jim Mattson <jmattson@google.com>]

Previously, if the hrtimer for the nested VMX-preemption timer fired
while L0 was emulating an L2 instruction with RFLAGS.TF set, the
synthesized single-step trap would be unceremoniously dropped when
synthesizing the "VMX-preemption timer expired" VM-exit from L2 to L1.

To fix this, don't synthesize a "VMX-preemption timer expired" VM-exit
from L2 to L1 when there is a pending debug trap, such as a
single-step trap.

Fixes: f4124500c2c13 ("KVM: nVMX: Fully emulate preemption timer")
Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Oliver Upton <oupton@google.com>
Reviewed-by: Peter Shier <pshier@google.com>
---
 arch/x86/kvm/vmx/nested.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index cbc9ea2de28f..6ab974debd44 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3690,7 +3690,9 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu)
 	    vmx->nested.preemption_timer_expired) {
 		if (block_nested_events)
 			return -EBUSY;
-		nested_vmx_vmexit(vcpu, EXIT_REASON_PREEMPTION_TIMER, 0, 0);
+		if (!vmx_pending_dbg_trap(vcpu))
+			nested_vmx_vmexit(vcpu, EXIT_REASON_PREEMPTION_TIMER,
+					  0, 0);
 		return 0;
 	}
 
-- 
2.26.0.110.g2183baf09c-goog