[PATCH 1/2] KVM: x86: Request event processing for exception VM-Exits

[Loc Nguyen <loc@ryzome.com>]

Request event processing whenever kvm_queue_exception_vmexit() queues an
exception VM-Exit.  Most callers reach the helper through
kvm_multiple_exception(), which already sets KVM_REQ_EVENT, but nested
asynchronous page faults call it directly.

Without another event request, vcpu_enter_guest() skips
kvm_check_and_inject_events() and re-enters L2.  A subsequent VM-Exit can
clear the pending exception while reconstructing vectoring state, losing
the synthetic #PF VM-Exit.  The APF reason remains PAGE_NOT_PRESENT and a
later regular #PF can consume the stale value.

Setting KVM_REQ_EVENT in the common helper ensures that L1 receives the
queued VM-Exit before KVM re-enters L2.

Fixes: 7709aba8f716 ("KVM: x86: Morph pending exceptions to pending VM-Exits at queue time")
Cc: stable@vger.kernel.org
Signed-off-by: Loc Nguyen <loc@ryzome.com>
---
 arch/x86/kvm/x86.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cf3fcdfd8ad2..376341a1ba04 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -450,6 +450,8 @@ static void kvm_queue_exception_vmexit(struct kvm_vcpu *vcpu, unsigned int vecto
 {
 	struct kvm_queued_exception *ex = &vcpu->arch.exception_vmexit;
 
+	kvm_make_request(KVM_REQ_EVENT, vcpu);
+
 	ex->vector = vector;
 	ex->injected = false;
 	ex->pending = true;
-- 
2.43.0