[PATCH v4 3/7] x86: KVM: clear interrupt shadow on EMULTYPE_SKIP

[Vitaly Kuznetsov <vkuznets@redhat.com>]

When doing x86_emulate_instruction(EMULTYPE_SKIP) interrupt shadow has to
be cleared if and only if the skipping is successful.

There are two immediate issues:
- In SVM skip_emulated_instruction() we are not zapping interrupt shadow
  in case kvm_emulate_instruction(EMULTYPE_SKIP) is used to advance RIP
  (!nrpip_save).
- In VMX handle_ept_misconfig() when running as a nested hypervisor we
  (static_cpu_has(X86_FEATURE_HYPERVISOR) case) forget to clear interrupt
  shadow.

Note that we intentionally don't handle the case when the skipped
instruction is supposed to prolong the interrupt shadow ("MOV/POP SS") as
skip-emulation of those instructions should not happen under normal
circumstances.

Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/kvm/x86.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e8f797fe9d9e..c2409d06c114 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6539,6 +6539,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 		kvm_rip_write(vcpu, ctxt->_eip);
 		if (ctxt->eflags & X86_EFLAGS_RF)
 			kvm_set_rflags(vcpu, ctxt->eflags & ~X86_EFLAGS_RF);
+		kvm_x86_ops->set_interrupt_shadow(vcpu, 0);
 		return EMULATE_DONE;
 	}
 
-- 
2.20.1