linux-kernel - Re: [PATCH] x86, microcode: Don't initialize microcode code on paravirt

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Date:	Mon, 1 Dec 2014 17:28:27 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	bp@...e.de, x86@...nel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, david.vrabel@...rix.com,
	konrad.wilk@...cle.com
Subject: Re: [PATCH] x86, microcode: Don't initialize microcode code on
 paravirt

On Mon, Dec 01, 2014 at 04:27:44PM -0500, Boris Ostrovsky wrote:
> Paravirtual guests are not expected to load microcode into processors
> and therefore it is not necessary to initialize microcode loading
> logic.
> 
> In fact, under certain circumstances initializing this logic may cause
> the guest to crash. Specifically, 32-bit kernels use __pa_nodebug()
> macro which does not work in Xen (the code path that leads to this macro
> happens during resume when we call mc_bp_resume()->load_ucode_ap()
> ->check_loader_disabled_ap())
> 
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> ---
>  arch/x86/kernel/cpu/microcode/core.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read Documentation/stable_kernel_rules.txt
for how to do this properly.

</formletter>
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