Re: Help With Identifying CPUID faulting logic in Xen code

[Fonyuy-Asheri Caleb <fonyuy-asheri.caleb@xxxxxxxx>]

Thank you

Caleb

----- Original Message -----
> From: "Andrew Cooper" <andrew.cooper3@xxxxxxxxxx>
> To: "Fonyuy-Asheri Caleb" <fonyuy-asheri.caleb@xxxxxxxx>, "xen-devel" 
> <xen-devel@xxxxxxxxxxxxxxxxxxxx>
> Cc: "Jan Beulich" <jbeulich@xxxxxxxx>
> Sent: Friday, January 3, 2025 3:35:43 PM
> Subject: Re: Help With Identifying CPUID faulting logic in Xen code

> On 03/01/2025 2:25 pm, Fonyuy-Asheri Caleb wrote:
>> Hello,
>>
>> I am interested in finding understanding how xen handles CPUID
>> faulting and
>> VM exits in general. Please can someone indicate to me the concerned
>> files?
>>
>> I want to know how xen detects the execution of the CPUID instruction and
>> ensures a guest only gets the features defined in cpuid-autogen.h file
>> depending on the guest type.
>>
>> I started looking at the file xen/arch/x86/cpuid.c but don't really
>> know which other
>> files to check next.
> 
> https://xenbits.xen.org/docs/unstable/features/feature-levelling.html
> 
> has a reasonable introduction.  Being nearly a decade old, it's slightly
> stale.  AMD now have CPUID Faulting capability too, new in Zen4 CPUs IIRC.
> 
> LCAP_faulting specifically is the constant you're looking for, in the
> Xen code.
> 
> ~Andrew