Re: [Xen-devel] [PATCH for-4.13] x86/AMD: unbreak CPU hotplug on AMD systems without RstrFpErrPtrs

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Nov 29, 2019 at 08:01:17PM +0000, Igor Druzhinin wrote:
> If the feature is not present Xen will try to force X86_BUG_FPU_PTRS
> feature at CPU identification time. This is especially noticeable in
> PV-shim that usually hotplugs its vCPUs. We either need to restrict this
> action for boot CPU only or allow secondary CPUs to modify
> forced CPU capabilities at runtime. Choose the latter accounting
> for potential microcode asymmetry between the boot and secondary CPUs.
> 
> Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>

LGTM, both setup_{force/clear}_cpu_cap are called from non-init
functions, albeit I'm not sure how well Xen and guests will deal with
a system that has such asymmetry in CPU features if APs don't have
RstrFpErrPtrs and the BSP does.

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Since I assume this fixes a page-fault, could you please paste part of
the crash trace to the commit message?

Thanks, Roger.

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