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Re: [PATCH v3 4/5] x86: Read MSR_ARCH_CAPS immediately after early_microcode_init()
- To: Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 22 Jun 2023 17:20:25 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 22 Jun 2023 15:20:53 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 22.06.2023 16:55, Alejandro Vallejo wrote:
> On Mon, Jun 19, 2023 at 05:57:14PM +0200, Jan Beulich wrote:
>>> + if ( boot_cpu_data.cpuid_level >= 7 )
>>> + boot_cpu_data.x86_capability[FEATURESET_7d0]
>>> + = cpuid_count_edx(7, 0);
>>
>> I take it we assume the maximum CPUID level won't go from below 7 to 7
>> or higher with the ucode update?
> Do you mean from >=7 to <7 instead? Otherwise it just works and I don't
> undertand the concern.
No, I mean going from <7 to >=7. In such a case the earlier
recorded .cpuid_level will prevent the leaf 7 read, and hence also
the possible discovery of ARCH_CAPS having appeared.
I actually wonder whether it wouldn't be better to re-run the whole
of early_cpu_init() from here again.
Jan
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