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

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Message-ID: <20171225145047.em6jihmfboszzp4z@pd.tnic>
Date:   Mon, 25 Dec 2017 15:50:47 +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 <tony.luck@...el.com>
Subject: Re: [PATCH v2] x86/microcode/intel: Blacklist the specific BDW-EP
 for late loading

On Mon, Dec 25, 2017 at 10:31:00PM +0800, Jia Zhang wrote:
> 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.

Yes, it probably will work in most cases because we do
collect_cpu_info() on init and we do refresh the microcode revision
after application but there might be some obscure case and configuration

  [ and the microcode loader has a gazillion possible use cases :-\ ]

where it might not work. That's why I mentioned doing it in
microcode_open() as a precation.

But we can leave that for later, if at all. This old method is deprecated
anyway.

-- 
Regards/Gruss,
    Boris.

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