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SubjectRe: [PATCH v7 06/13] KVM: x86: Add Intel Processor Trace virtualization mode
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On 03/05/2018 13:32, Alexander Shishkin wrote:
>> +static inline bool cpu_has_vmx_pt_use_gpa(void)
>> +{
>> + return vmcs_config.cpu_based_2nd_exec_ctrl & SECONDARY_EXEC_PT_USE_GPA;
>> +}
>
> I can deduce the meaning of the previous one, but not this one, and there's
> no explanation.

Within KVM, GPA always means guest physical address.

>> + if (pt_mode == PT_MODE_SYSTEM)
>> + vmexit_control &= ~(VM_EXIT_CLEAR_IA32_RTIT_CTL |
>> + VM_EXIT_PT_CONCEAL_PIP);
>
> Ok, so what we really want to know is: is there an encompassing PT
> event on this cpu when we go into VMLAUNCH/VMRESTORE, right?
> We can find this out from the pt_ctx and avoid the pt_mode entirely.
> IOW, instead of having the 3 modes that you describe at the top, you
> can use something like the following:
>
> 1. Do we have an event in pt_ctx?
> * No -> Set up the context for VMX.
> * Yes -> 2. Is attr.exclude_guest set?
> * No -> Guest trace goes to the host's buffer, do nothing.
> * Yes -> Set up/switch the context for VMX.

Can you explain this more clearly?

Thanks,

Paolo

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