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Re: [PATCH 5/8] x86: rename ARAT feature flag
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 19 Nov 2025 08:31:31 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 19 Nov 2025 07:31:41 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 18.11.2025 17:38, Andrew Cooper wrote:
> On 18/11/2025 3:07 pm, Jan Beulich wrote:
>> Add a XEN infix, to properly distinguish it from the CPUID feature flag
>> (leaf 6 EAX bit 2).
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> Question is whether we still need opt_arat (and the command line option),
>> or whether we could go directly from the CPUID bit (overriding it to on
>> for older AMD [and Hygon?] CPUs). Or whether to have opt_arat affect the
>> (host) CPU policy directly.
>
> I have no particular love for opt_arat. I added it when there was no
> way to force a system to fall back to an older timer.
>
> As long as we've got some way of configuring the exact timer to, I'm not
> fussed about keeping the top level boolean.
But the question is what the replacement would look like. Is it okay to
override bits to true in the host policy? (It may be as long as we don't
expose this in the guest policies, but at some point we may want or even
need to.) Would the command line option also go away (in favor of
integrating with cpuid=, which would require extra logic as long as we
don't put leaf 6 bits in public/arch-x86/cpufeatureset.h)?
IOW for the patch at hand I wouldn't mean to make adjustments. The remark
was more towards further, future adjustments.
Jan
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