Re: [PATCH v7 3/3] KVM: vmx: handle vm-exit for UMWAIT and TPAUSE

[Tao Xu]

On 7/13/2019 12:03 AM, Sean Christopherson wrote:
> On Fri, Jul 12, 2019 at 04:29:07PM +0800, Tao Xu wrote:
> > --- a/arch/x86/kvm/vmx/nested.c
> > +++ b/arch/x86/kvm/vmx/nested.c
> > @@ -5213,6 +5213,9 @@ bool nested_vmx_exit_reflected(struct kvm_vcpu *vcpu, u32 exit_reason)
> >   	case EXIT_REASON_ENCLS:
> >   		/* SGX is never exposed to L1 */
> >   		return false;
> > +	case EXIT_REASON_UMWAIT: case EXIT_REASON_TPAUSE:
>
> Grouped case statements are usually stacked vertically, e.g.:
>
> 	case EXIT_REASON_UMWAIT:
> 	case EXIT_REASON_TPAUSE:
> Ok, thank you for your suggestion.

> > +		return nested_cpu_has2(vmcs12,
> > +			SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE);
> >   	default:
> >   		return true;
> >   	}
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index 0787f140d155..e026b1313dc3 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -5349,6 +5349,20 @@ static int handle_monitor(struct kvm_vcpu *vcpu)
> >   	return handle_nop(vcpu);
> >   }
> >   
> > +static int handle_umwait(struct kvm_vcpu *vcpu)
> > +{
> > +	kvm_skip_emulated_instruction(vcpu);
> > +	WARN(1, "this should never happen\n");
>
> Blech.  I'm guessing this code was copy-pasted from handle_xsaves() and
> handle_xrstors().  The blurb of "this should never happen" isn't very
> helpful, e.g. the WARN itself makes it pretty obvious that we don't expect
> to reach this point.  WARN_ONCE would also be preferable, no need to spam
> the log in the event things go completely haywire.
>
> Rather than propagate ugly code, what about defining a common helper, e.g.
>
> static int handle_unexpected_vmexit(struct kvm_vcpu *vcpu)
> {
> 	kvm_skip_emulated_instruction(vcpu);
> 	WARN_ONCE(1, "Unexpected VM-Exit = 0x%x", vmcs_read32(VM_EXIT_REASON));
> 	return 1;
> }
>
> ...
> {
> 	[EXIT_REASON_XSAVES]                  = handle_unexpected_vmexit,
> 	[EXIT_REASON_XRSTORS]                 = handle_unexpected_vmexit,
>
> 	[EXIT_REASON_UMWAIT]                  = handle_unexpected_vmexit,
> 	[EXIT_REASON_TPAUSE]                  = handle_unexpected_vmexit,
>
> }
Thank you Sean, I will do this in next version of patch.

> > +	return 1;
> > +}
> > +
> > +static int handle_tpause(struct kvm_vcpu *vcpu)
> > +{
> > +	kvm_skip_emulated_instruction(vcpu);
> > +	WARN(1, "this should never happen\n");
> > +	return 1;
> > +}
> > +
> >   static int handle_invpcid(struct kvm_vcpu *vcpu)
> >   {
> >   	u32 vmx_instruction_info;
> > @@ -5559,6 +5573,8 @@ static int (*kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
> >   	[EXIT_REASON_VMFUNC]		      = handle_vmx_instruction,
> >   	[EXIT_REASON_PREEMPTION_TIMER]	      = handle_preemption_timer,
> >   	[EXIT_REASON_ENCLS]		      = handle_encls,
> > +	[EXIT_REASON_UMWAIT]                  = handle_umwait,
> > +	[EXIT_REASON_TPAUSE]                  = handle_tpause,
> >   };
> >   
> >   static const int kvm_vmx_max_exit_handlers =
> > --
> > 2.20.1