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SubjectRe: [PATCH 3/9] KVM: x86: add pcommit support
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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 “PCOMMIT exiting”) is
| always the same as CPUID.07H:EBX.PCOMMIT[bit 22]. Thus, software can set “PCOMMIT exiting” to 1
| if and only if the PCOMMIT instruction is enumerated via CPUID


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