Re: [PATCH 10/16] x86/amd: Always probe and configure the masking MSRs

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.01.2026 18:53, Andrew Cooper wrote:
> This allows the infrastructure to reused for system-wide quirk/errata
> adjustments.
> 
> Replace the call to ctxt_switch_levelling() with amd_ctxt_switch_masking()
> instead.  The CPUID Faulting aspect is not interesting at this point in boot,
> and we want to explicitly propagate the masking MSR defaults into APs.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
with two comment nits:

> --- a/xen/arch/x86/cpu/amd.c
> +++ b/xen/arch/x86/cpu/amd.c
> @@ -162,7 +162,7 @@ static void __init noinline probe_masking_msrs(void)
>   * parameter of NULL is used to context switch to the default host state (by
>   * the cpu bringup-code, crash path, etc).
>   */
> -static void cf_check amd_ctxt_switch_masking(const struct vcpu *next)
> +void cf_check amd_ctxt_switch_masking(const struct vcpu *next)
>  {
>       struct cpuidmasks *these_masks = &this_cpu(cpuidmasks);
>       const struct domain *nextd = next ? next->domain : NULL;
> @@ -242,9 +242,12 @@ static void __init amd_init_levelling(void)
>           boot_cpu_has(X86_FEATURE_CPUID_USER_DIS)) {
>               expected_levelling_cap |= LCAP_faulting;
>               levelling_caps |= LCAP_faulting;
> -             return;
>       }
>  
> +     /*
> +      * Always probe for the MSRs too.  We reuse the infrastruture for
> +      * quirks/errata/etc during boot.
> +      */
>       probe_masking_msrs();

This isn't just about boot, but also soft-onlining of CPUs and S3 resume.

> @@ -1015,7 +1018,11 @@ static void cf_check init_amd(struct cpuinfo_x86 *c)
>       u32 l, h;
>       uint64_t value;
>  
> -     ctxt_switch_levelling(NULL);
> +     /*
> +      * Reuse amd_ctxt_switch_masking() explicitly.  This propagates
> +      * quirk/errata adjustments made duing early_init_amd() into the APs.
> +      */
> +     amd_ctxt_switch_masking(NULL);

Have the same comment also ...

> --- a/xen/arch/x86/cpu/hygon.c
> +++ b/xen/arch/x86/cpu/hygon.c
> @@ -32,7 +32,7 @@ static void cf_check init_hygon(struct cpuinfo_x86 *c)
>  {
>       unsigned long long value;
>  
> -     ctxt_switch_levelling(NULL);
> +     amd_ctxt_switch_masking(NULL);

... here?

Jan