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Re: [PATCH 5/6] x86/boot: Record MSR_ARCH_CAPS for the Raw and Host CPU policy
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 16 May 2023 13:59:07 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 16 May 2023 12:59:32 +0000
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On 16/05/2023 1:53 pm, Jan Beulich wrote:
> On 15.05.2023 16:42, Andrew Cooper wrote:
>> Extend x86_cpu_policy_fill_native() with a read of ARCH_CAPS based on the
>> CPUID information just read, which removes the need handling it specially in
>> calculate_raw_cpu_policy().
>>
>> Extend generic_identify() to read ARCH_CAPS into x86_capability[], which is
>> fed into the Host Policy. This in turn means there's no need to special case
>> arch_caps in calculate_host_policy().
>>
>> No practical change.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Thanks.
>
> I have a question though, which I think would be nice if the description
> had covered:
>
>> --- a/xen/lib/x86/cpuid.c
>> +++ b/xen/lib/x86/cpuid.c
>> @@ -226,7 +226,12 @@ void x86_cpu_policy_fill_native(struct cpu_policy *p)
>> p->hv_limit = 0;
>> p->hv2_limit = 0;
>>
>> - /* TODO MSRs */
>> +#ifdef __XEN__
>> + /* TODO MSR_PLATFORM_INFO */
>> +
>> + if ( p->feat.arch_caps )
>> + rdmsrl(MSR_ARCH_CAPABILITIES, p->arch_caps.raw);
>> +#endif
> What about non-Xen environments re-using this code? In particular the
> test harnesses would be nice if they didn't run with the two fields
> all blank at all times.
Right now, I don't have an answer.
In Linux in lockdown mode, there isn't even a way to access this info
userspace, because /proc/cpu/$/msr goes away.
It's only a unit test, and this doesn't break it.
~Andrew
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