linux-kernel - Re: [PATCH v2] x86/microcode/intel: Blacklist the specific BDW-EP for late loading

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Date:   Mon, 25 Dec 2017 22:31:00 +0800
From:   "Jia Zhang" <qianyue.zj@...baba-inc.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH v2] x86/microcode/intel: Blacklist the specific BDW-EP for
 late loading



在 2017/12/25 下午9:34, Borislav Petkov 写道:
> + Tony.
> 
> On Mon, Dec 25, 2017 at 03:49:29PM +0800, Jia Zhang wrote:
>> Instead of blacklisting all Broadwell processorsi for running a late
>> loading, only BDW-EP (signature 406f1) with the microcode version
>> 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..f80b2dd 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
>> +	 * 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 && intel_get_microcode_revision() < 0x0b000021U) {
> 
> Actually, you shouldn't need to call intel_get_microcode_revision() here
> as collect_cpu_info() has done that already and the revision is in
> 
> 	c->microcode
> 
> unless you're using the old method through do_microcode_update() and
> for that you'll need to call collect_cpu_info() over all CPUs in
> microcode_open().
> 
> So how do you update your microcode?

I used the interface /sys/devices/system/cpu/microcode/reload, not
/dev/cpu/microcode.

Sound like using c->microcode is already enough. So I'm not sure why
calling collect_cpu_info() is necessary for the old method. c->microcode
can reflect the correct version as long as it always syncs up with the
recent loaded microcode update.

Thanks,
Jia

>