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Re: [PATCH 4/4] x86/spec-ctrl: Remove opencoded MSR_ARCH_CAPS check
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 17 May 2023 17:35:30 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 17 May 2023 16:35:55 +0000
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On 17/05/2023 3:47 pm, Jan Beulich wrote:
> On 16.05.2023 16:53, Andrew Cooper wrote:
>> @@ -401,6 +400,8 @@ static void __init print_details(enum ind_thunk thunk,
>> uint64_t caps)
>> cpuid_count(7, 2, &tmp, &tmp, &tmp, &_7d2);
>> if ( boot_cpu_data.extended_cpuid_level >= 0x80000008 )
>> cpuid(0x80000008, &tmp, &e8b, &tmp, &tmp);
>> + if ( cpu_has_arch_caps )
>> + rdmsrl(MSR_ARCH_CAPABILITIES, caps);
> Why do you read the MSR again? I would have expected this to come out
> of raw_cpu_policy now (and incrementally the CPUID pieces as well,
> later on).
Consistency with the surrounding logic.
Also because the raw and host policies don't get sorted until much later
in boot.
> Apart from this, with all the uses further down gone, perhaps there's
> not even a need for the raw value, if you used the bitfields in the
> printk(). Which in turn raises the question whether the #define-s in
> msr-index.h are of much use then anymore.
One of the next phases of work is synthesizing these in the host policy
for CPUs which didn't receive microcode updates (for whatever reason).
There is a valid discussion for whether we ought to render the raw or
host info here (currently we do raw), but I'm not adjusting that in this
patch.
~Andrew
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