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Re: [PATCH v2 2/4] x86: Read MSR_ARCH_CAPS after early_microcode_init()
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 13 Jun 2023 08:40:48 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 13 Jun 2023 06:41:00 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 12.06.2023 20:25, Andrew Cooper wrote:
> On 12/06/2023 4:46 pm, Jan Beulich wrote:
>> On 05.06.2023 19:08, Alejandro Vallejo wrote:
>>> @@ -878,5 +887,17 @@ int __init early_microcode_init(unsigned long
>>> *module_map,
>>> if ( ucode_mod.mod_end || ucode_blob.size )
>>> rc = early_microcode_update_cpu();
>>>
>>> + early_read_cpuid_7d0();
>>> +
>>> + /*
>>> + * tsx_init() needs MSR_ARCH_CAPS, but it runs before identify_cpu()
>>> + * populates boot_cpu_data, so we read it here to centralize early
>>> + * CPUID/MSR reads in the same place.
>>> + */
>>> + if ( cpu_has_arch_caps )
>>> + rdmsr(MSR_ARCH_CAPABILITIES,
>>> + boot_cpu_data.x86_capability[FEATURESET_m10Al],
>>> + boot_cpu_data.x86_capability[FEATURESET_m10Ah]);
>> ... "centralize" aspect goes away, and hence the comment needs adjusting.
>
> I find it weird splitting apart the various reads into x86_capability[],
> but in light of the feedback, only the rdmsr() needs to stay.
Hmm, wait: When updating a CPU from a pre-arch-caps ucode level on one
that supports arch-caps, don't we need to re-read 7d0 here? (I.e. the
call to early_read_cpuid_7d0() needs to stay, but for a reason
different from the one presently stated in the description, and
possibly even worth a brief comment.)
Jan
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