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Re: [PATCH] x86/ucode: Fix stability of the Raw CPU Policy rescan


  • To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Wed, 24 Jan 2024 16:37:19 +0100
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  • Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Wed, 24 Jan 2024 15:37:27 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 23.01.2024 21:59, Andrew Cooper wrote:
> Always run microcode_update_helper() on the BSP, so the the updated Raw CPU
> policy doesn't get non-BSP topology details included.

Wouldn't it be better (and consistent with ...

> Have calculate_raw_cpu_policy() clear the instantanious XSTATE sizes.  The
> value XCR0 | MSR_XSS had when we scanned the policy isn't terribly interesting
> to report.

... this) to purge these details from the raw policy as well then?

> When CPUID Masking is active, it affects CPUID instructions issued by Xen
> too.  Transiently disable masking to get a clean scan.
> 
> Fixes: 694d79ed5aac ("x86/ucode: Refresh raw CPU policy after microcode load")
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Irrespective of the question above, I'm also okay with the change as is:
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan



 


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