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Re: file xen/include/xen/lib/x86/cpu-policy.h: Meaning of CPUID constants


  • To: Fonyuy-Asheri Caleb <fonyuy-asheri.caleb@xxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Mon, 6 May 2024 10:47:39 +0200
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  • Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Mon, 06 May 2024 08:47:44 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 06.05.2024 10:45, Fonyuy-Asheri Caleb wrote:
>> From: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
>> Sent: Monday, May 6, 2024 10:34:20 AM
> 
>> For basic leaves (0x000000xx) we support up to leaf 0xd (XSTATE).  It
>> doesn't mean there are no further leaves behind it, but we likely
>> still have no use for them, and hence they are not part of the policy.
>> The cpu-policy is used to store a (cpuid) policy object for guests,
>> so if the information exposed in those leaves are related to features
>> that are never exposed to guests is makes no sense to have space for
>> them.
> 
> So if I understand you well, you mean before extending this, we need to 
> perform a study on the 
> leaves to confirm how useful they are to the guests depending on the cpu 
> information they carry. 

It's not only question of usefulness, but of correctness. We can't blindly
expose leaves.

Jan



 


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