Re: [PATCH 3/9] KVM: x86: add pcommit support

[Xiao Guangrong]

On 09/07/2015 07:18 PM, Paolo Bonzini wrote:

> > +static int handle_pcommit(struct kvm_vcpu *vcpu)
> > +{
> > +	/* we never catch pcommit instruct for L1 guest. */
> > +	BUG();
>
> Please WARN instead.

Okay.

> > +	return 1;
> > +}
> > +
> >   /*
> >    * The exit handlers return 1 if the exit was handled fully and guest execution
> >    * may resume.  Otherwise they set the kvm_run parameter to indicate what needs
> > @@ -7258,6 +7269,7 @@ static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
> >   	[EXIT_REASON_XSAVES]                  = handle_xsaves,
> >   	[EXIT_REASON_XRSTORS]                 = handle_xrstors,
> >   	[EXIT_REASON_PML_FULL]		      = handle_pml_full,
> > +	[EXIT_REASON_PCOMMIT]                 = handle_pcommit,
> >   };
> >
> >   static const int kvm_vmx_max_exit_handlers =
> > @@ -7559,6 +7571,8 @@ static bool nested_vmx_exit_handled(struct kvm_vcpu *vcpu)
> >   		 * the XSS exit bitmap in vmcs12.
> >   		 */
> >   		return nested_cpu_has2(vmcs12, SECONDARY_EXEC_XSAVES);
> > +	case EXIT_REASON_PCOMMIT:
> > +		return nested_cpu_has2(vmcs12, SECONDARY_EXEC_PCOMMIT);
> >   	default:
> >   		return true;
> >   	}
> > @@ -8688,6 +8702,10 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
> >   		if (best)
> >   			best->ebx &= ~bit(X86_FEATURE_INVPCID);
> >   	}
> > +
> > +	if (!guest_cpuid_has_pcommit(vcpu) && nested)
> > +		vmx->nested.nested_vmx_secondary_ctls_high &=
> > +			~SECONDARY_EXEC_PCOMMIT;
>
> Why is this needed?

If pcommit is not allowed in L1 guest, L1 is not allowed to intercept pcommit
for L2.

BTW, the spec saied:

| IA32_VMX_PROCBASED_CTLS2[53] (which enumerates support for the 1-setting of âPCOMMIT exitingâ) is
| always the same as CPUID.07H:EBX.PCOMMIT[bit 22]. Thus, software can set âPCOMMIT exitingâ to 1
| if and only if the PCOMMIT instruction is enumerated via CPUID
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