linux-kernel - Re: [PATCH -v2 1/2] x86, microcode: Sanitize per-cpu microcode reloading interface

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Message-ID: <1340280742.18025.5.camel@twins>
Date:	Thu, 21 Jun 2012 14:12:22 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Borislav Petkov <bp@...64.org>
Cc:	X86-ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Borislav Petkov <borislav.petkov@....com>,
	Henrique de Moraes Holschuh <hmh@....eng.br>
Subject: Re: [PATCH -v2 1/2] x86, microcode: Sanitize per-cpu microcode
 reloading interface

On Thu, 2012-06-21 at 14:07 +0200, Borislav Petkov wrote:
> From: Borislav Petkov <borislav.petkov@....com>
> 
> Microcode reloading in a per-core manner is a very bad idea for both
> major x86 vendors. And the thing is, we have such interface with which
> we can end up with different microcode versions applied on different
> cores of an otherwise homogeneous wrt (family,model,stepping) system.
> 
> So turn off the possibility of doing that per core and allow it only
> system-wide.
> 
> This is a minimal fix which we'd like to see in stable too thus the
> more-or-less arbitrary decision to allow system-wide reloading only on
> the BSP:
> 
> $ echo 1 > /sys/devices/system/cpu/cpu0/microcode/reload
> ...
> 
> and disable the interface on the other cores:
> 
> $ echo 1 > /sys/devices/system/cpu/cpu23/microcode/reload
> -bash: echo: write error: Invalid argument
> 
> Also, allowing the reload only from one CPU (the BSP in
> that case) doesn't allow the reload procedure to degenerate
> into an O(n^2) deal when triggering reloads from all
> /sys/devices/system/cpu/cpuX/microcode/reload sysfs nodes
> simultaneously.
> 
> A more generic fix will follow.
> 
> Cc: Henrique de Moraes Holschuh <hmh@....eng.br>
Acked-by: Peter Zijlstra <peterz@...radead.org> 
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