Re: [PATCH v2] arch/x86: Fix boot_cpu_data.microcode version output

[Oleksandr Natalenko <oleksandr@natalenko.name>]

Hi.

> I tested this on AMD Ryzen & Intel Broadwell system and dumped the
> boot_cpu_data before and after a microcode update.  On the Intel
> system I also did a fatal MCE using mce-inject to confirm the output
> from the mce handling code.
> 
> P.
> 
> ---8<---
> 
> On systems where a runtime microcode update has occurred the microcode
> version output in a MCE log record is wrong because
> boot_cpu_data.microcode is not updated during runtime.
> 
> Update boot_cpu_data.microcode when the BSP's microcode is updated.
> 
> Fixes: fa94d0c6e0f3 ("x86/MCE: Save microcode revision in machine check 
> records")
> Suggested-by: Borislav Petkov <bp@alien8.com>
> Signed-off-by: Prarit Bhargava <prarit@redhat.com>
> Cc: stable@vger.kernel.org
> Cc: sironi@amazon.de
> Cc: tony.luck@intel.com
> ---
> Changes in v2: Use mc_amd->hdr.patch_id on AMD
> 
>  arch/x86/kernel/cpu/microcode/amd.c   | 4 ++++
>  arch/x86/kernel/cpu/microcode/intel.c | 4 ++++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/microcode/amd.c 
> b/arch/x86/kernel/cpu/microcode/amd.c
> index 0624957aa068..63b072377ba4 100644
> --- a/arch/x86/kernel/cpu/microcode/amd.c
> +++ b/arch/x86/kernel/cpu/microcode/amd.c
> @@ -537,6 +537,10 @@ static enum ucode_state apply_microcode_amd(int 
> cpu)
>  	uci->cpu_sig.rev = mc_amd->hdr.patch_id;
>  	c->microcode = mc_amd->hdr.patch_id;
> 
> +	/* Update boot_cpu_data's revision too, if we're on the BSP: */
> +	if (c->cpu_index == boot_cpu_data.cpu_index)
> +		boot_cpu_data.microcode =  mc_amd->hdr.patch_id;
> +
>  	return UCODE_UPDATED;
>  }
> 
> diff --git a/arch/x86/kernel/cpu/microcode/intel.c 
> b/arch/x86/kernel/cpu/microcode/intel.c
> index 97ccf4c3b45b..256d336cbc04 100644
> --- a/arch/x86/kernel/cpu/microcode/intel.c
> +++ b/arch/x86/kernel/cpu/microcode/intel.c
> @@ -851,6 +851,10 @@ static enum ucode_state apply_microcode_intel(int 
> cpu)
>  	uci->cpu_sig.rev = rev;
>  	c->microcode = rev;
> 
> +	/* Update boot_cpu_data's revision too, if we're on the BSP: */
> +	if (c->cpu_index == boot_cpu_data.cpu_index)
> +		boot_cpu_data.microcode = rev;
> +
>  	return UCODE_UPDATED;
>  }
> 
> --
> 2.17.0

After this patch, do we preserve an original microcode version 
somewhere? If no, why? Sometimes it is useful while debugging another 
crash because of faulty microcode.

Thanks.

-- 
   Oleksandr Natalenko (post-factum)