Re: [Xen-devel] [PATCH] x86, amd_ucode: Skip microcode updates for final levels

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 07/30/2015 12:23 PM, Aravind Gopalakrishnan wrote:
> Some of older[Fam10h] systems require that the microcode versions
> that it comes up with should not be updated by the microcode driver.
> Otherwise, system hangs are known to occur.
>
> In this patch, we check for those microcode versions and abort the
> update process if existing microcode level is already applied by
> the BIOS.
>
> A linux version of the patch has already made it into tip-
> http://marc.info/?l=linux-kernel&m=143703405627170
>
> Signed-off-by: Aravind Gopalakrishnan <aravind.gopalakrishnan@xxxxxxx>
> ---
>   xen/arch/x86/microcode_amd.c | 31 +++++++++++++++++++++++++++++++
>   1 file changed, 31 insertions(+)
>
> diff --git a/xen/arch/x86/microcode_amd.c b/xen/arch/x86/microcode_amd.c
> index f79b397..c958a47 100644
> --- a/xen/arch/x86/microcode_amd.c
> +++ b/xen/arch/x86/microcode_amd.c
> @@ -347,6 +347,30 @@ static int container_fast_forward(const void *data, size_t 
> size_left, size_t *of
>       return 0;
>   }
>   
> +static unsigned int final_levels[] = {
> +    0x01000098,
> +    0x0100009f,
> +    0x010000af,
> +    0
> +};
Are these values documented somewhere?

-boris


> +
> +static bool_t check_final_patch_levels(int cpu)
> +{
> +    /*
> +     * Check the current patch levels on the cpu. If they are equal to
> +     * any of the 'final_levels', then we should not update the microcode
> +     * patch on the cpu as system will hang otherwise.
> +     */
> +    struct ucode_cpu_info *uci = &per_cpu(ucode_cpu_info, cpu);
> +    int i;
> +
> +    for ( i = 0; final_levels[i]; i++ )
> +        if ( uci->cpu_sig.rev == final_levels[i] )
> +            return 1;
> +
> +    return 0;
> +}
> +
>   static int cpu_request_microcode(int cpu, const void *buf, size_t bufsize)
>   {
>       struct microcode_amd *mc_amd, *mc_old;
> @@ -369,6 +393,13 @@ static int cpu_request_microcode(int cpu, const void *buf, 
> size_t bufsize)
>           goto out;
>       }
>   
> +    if ( check_final_patch_levels(cpu) )
> +    {
> +        pr_debug("microcode: Cannot update microcode patch on the cpu as we hit a 
> final level\n");
> +        error = -EPERM;
> +        goto out;
> +    }
> +
>       mc_amd = xmalloc(struct microcode_amd);
>       if ( !mc_amd )
>       {

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