linux-kernel - Re: [PATCH v3] x86/microcode/intel: Blacklist the specific BDW-EP for late loading

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Date:   Tue, 26 Dec 2017 11:51:44 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Jia Zhang <qianyue.zj@...baba-inc.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, linux-kernel@...r.kernel.org, tony.luck@...el.com
Subject: Re: [PATCH v3] x86/microcode/intel: Blacklist the specific BDW-EP
 for late loading

On Tue, Dec 26, 2017 at 09:44:31AM +0800, Jia Zhang wrote:
> Instead of blacklisting all Broadwell processorsi for running a late
					^^^^^^^^^^^

Please run all text in this patch through a spellchecker.

> loading, only BDW-EP (signature 406f1) with the microcode version

Please write out what that signature actually is - it might be confusing
to people not dealing with family/model/stepping on a daily basis.

> less than 0x0b000021 needs to be blacklisted.
> 
> This is documented in the the public documentation #334165 (See the
> item BDF90 for details).
> 
> Signed-off-by: Jia Zhang <qianyue.zj@...baba-inc.com>
> ---
>  arch/x86/kernel/cpu/microcode/intel.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
> index 8ccdca6..d2c1638 100644
> --- a/arch/x86/kernel/cpu/microcode/intel.c
> +++ b/arch/x86/kernel/cpu/microcode/intel.c
> @@ -910,8 +910,15 @@ static bool is_blacklisted(unsigned int cpu)
>  {
>  	struct cpuinfo_x86 *c = &cpu_data(cpu);
>  
> -	if (c->x86 == 6 && c->x86_model == INTEL_FAM6_BROADWELL_X) {
> -		pr_err_once("late loading on model 79 is disabled.\n");
> +	/*
> +	 * The Broadwell-EP processor with the microcode version less
> +	 * then 0x0b000021 may reault in system hang when running a late
			       ^^^^^^
typo.

> +	 * loading. This behavior is documented in item BDF90, #334165
> +	 * (Intel Xeon Processor E7-8800/4800 v4 Product Family).
> +	 */
> +	if (c->x86 == 6 && c->x86_model == INTEL_FAM6_BROADWELL_X &&
> +	    c->x86_mask == 0x01 && c->microcode < 0x0b000021U) {
							    ^

The appended 'U' is for? I mean, I'd expect the implicit promotion rules
to kick in here as always. :-)

> +		pr_err_once("late loading on model 79 (sig 64f1) is disabled.\n");

See, you can get the sig wrong yourself too. Or were you trying to write
family/model/stepping in some short form?

Also, this error message needs to explain exactly why late loading is
disabled - because microcode revision is < 0x0b000021.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.