Re: [Xen-devel] [PATCH v2] x86/AMD: unbreak CPU hotplug on AMD systems without RstrFpErrPtrs

[Jan Beulich <jbeulich@xxxxxxxx>]

On 04.12.2019 00:56, 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 former since modifying
> forced capabilities out of boot path leaves the system in potentially
> inconsistent state.
> 
> Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>

I've committed this to unstable, as per the outcome of the
community call. What about this for 4.13? Iirc the breakage was
introduced during this development cycle.

Jan

> ---
> Changes in v2:
> - pick the former approach instead of the latter
> ---
>  xen/arch/x86/cpu/amd.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/xen/arch/x86/cpu/amd.c b/xen/arch/x86/cpu/amd.c
> index fec2830..8b5f0f2 100644
> --- a/xen/arch/x86/cpu/amd.c
> +++ b/xen/arch/x86/cpu/amd.c
> @@ -583,7 +583,7 @@ static void init_amd(struct cpuinfo_x86 *c)
>        * Older AMD CPUs don't save/load FOP/FIP/FDP unless an FPU exception
>        * is pending.  Xen works around this at (F)XRSTOR time.
>        */
> -     if (!cpu_has(c, X86_FEATURE_RSTR_FP_ERR_PTRS))
> +     if (c == &boot_cpu_data && !cpu_has(c, X86_FEATURE_RSTR_FP_ERR_PTRS))
>               setup_force_cpu_cap(X86_BUG_FPU_PTRS);
>  
>       /*
> 


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