Re: [Xen-devel] [PATCH v10 15/16] microcode: disable late loading if CPUs are affected by BDF90

[Jan Beulich <jbeulich@xxxxxxxx>]

On 12.09.2019 09:22, Chao Gao wrote:
> @@ -283,6 +284,27 @@ static enum microcode_match_result compare_patch(
>                                                               : OLD_UCODE;
>  }
>  
> +static bool is_blacklisted(void)
> +{
> +    struct cpuinfo_x86 *c = &current_cpu_data;
> +    uint64_t llc_size = c->x86_cache_size * 1024ULL;
> +    struct cpu_signature *sig = &this_cpu(cpu_sig);
> +
> +    do_div(llc_size, c->x86_max_cores);
> +
> +    /*
> +     * Late loading on model 79 with microcode revision less than 0x0b000021
> +     * and LLC size per core bigger than 2.5MB may result in a system hang.
> +     * This behavior is documented in item BDF90, #334165 (Intel Xeon
> +     * Processor E7-8800/4800 v4 Product Family).
> +     */
> +    if ( c->x86 == 6 && c->x86_model == 0x4F && c->x86_mask == 0x1 &&
> +         llc_size > 2621440 && sig->rev < 0x0b000021 )
> +        return true;
> +
> +    return false;
> +}

Isn't this misbehavior worked around by the wbinvd() you add in the next
patch?

> --- a/xen/include/asm-x86/microcode.h
> +++ b/xen/include/asm-x86/microcode.h
> @@ -30,6 +30,7 @@ struct microcode_ops {
>      bool (*match_cpu)(const struct microcode_patch *patch);
>      enum microcode_match_result (*compare_patch)(
>          const struct microcode_patch *new, const struct microcode_patch 
> *old);
> +    bool (*is_blacklisted)(void);

Why a hook rather than a boolean flag, which could be set by
microcode_update_one() (as invoked during AP bringup)?

Jan

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