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Re: [PATCH v2] x86/ucode: Refresh raw CPU policy after microcode load
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Thu, 4 May 2023 12:47:45 +0200
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Wei Liu <wl@xxxxxxx>
- Delivery-date: Thu, 04 May 2023 10:48:13 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Thu, May 04, 2023 at 11:26:07AM +0100, Andrew Cooper wrote:
> Loading microcode can cause new features to appear. This has happened
> routinely since Spectre/Meltdown, and even the presence of new status bits can
> sometimes mean the administrator has no further actions to perform.
>
> Conversely, loading microcode can occasionally cause features to disappear.
> As with livepatching, it is very much the administrators responsibility to
> confirm that a late microcode load is safe on the intended system before
> rolling it out in production.
>
> Refresh the raw CPU policy after late microcode load appears to have done
> something, so xen-cpuid can reflect the updated state of the system.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
I'm not fully sure it's worth calling calculate_raw_cpu_policy() if
updated != nr_cores, as it's possible the current CPU where the policy
is regenerated hasn't been updated.
Thanks, Roger.
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