Re: [PATCH v2 3/5] x86: KVM: clear interrupt shadow on EMULTYPE_SKIP

Sean Christopherson
2019-08-06T15:45:42Z

On Tue, Aug 06, 2019 at 08:01:48AM +0200, Vitaly Kuznetsov wrote:
> 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) we forget to clear

Redundant 'we'. Might be worth adding a blurb in the changelog to note
that this intentionally doesn't handle "MOV/POP SS" as skip-emulation of
those instructions can only occur if the guest is doing something silly.

Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>

> interrupt shadow.
>
> Suggested-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 c6d951cbd76c..eac8253d84d2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6537,6 +6537,7 @@ 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
>