Re: [PATCH] x86/ucode: Further fixes to identify "ucode already up to date"

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.05.2024 13:31, Andrew Cooper wrote:
> When the revision in hardware is newer than anything Xen has to hand,
> 'microcode_cache' isn't set up.  Then, `xen-ucode` initiates the update
> because it doesn't know whether the revisions across the system are symmetric
> or not.  This involves the patch getting all the way into the
> apply_microcode() hooks before being found to be too old.
> 
> This is all a giant mess and needs an overhaul, but in the short term simply
> adjust the apply_microcode() to return -EEXIST.
> 
> Also, unconditionally print the preexisting microcode revision on boot.  It's
> relevant information which is otherwise unavailable if Xen doesn't find new
> microcode to use.

Since you do this for the BSP only, I'm okay with that. Doing this for all
CPUs would have added too much verbosity imo, and I would then have asked
to log the pre-existing revision only when no update would be done by us.

> Fixes: 648db37a155a ("x86/ucode: Distinguish "ucode already up to date"")
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
with one small request related to the remark above:

> --- a/xen/arch/x86/cpu/microcode/core.c
> +++ b/xen/arch/x86/cpu/microcode/core.c
> @@ -881,6 +881,8 @@ int __init early_microcode_init(unsigned long *module_map,
>  
>      ucode_ops.collect_cpu_info();
>  
> +    printk(XENLOG_INFO "Boot microcode revision: 0x%08x\n", 
> this_cpu(cpu_sig).rev);

Can this please be "BSP" or "Boot CPU" instead of just "Boot", to clarify
which CPU's information this is? I'm pretty sure you too have hit systems
where firmware doesn't update all cores.

Jan