linux-kernel - Re: [PATCH 2/2] x86/microcode: Do not exit early from __reload

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Date:   Fri, 20 Apr 2018 09:00:18 -0700
From:   "Raj, Ashok" <ashok.raj@...el.com>
To:     Borislav Petkov <bp@...e.de>
Cc:     Vitezslav Samel <vitezslav@...el.cz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, x86-ml <x86@...nel.org>
Subject: Re: [PATCH 2/2] x86/microcode: Do not exit early from __reload_late()

On Fri, Apr 20, 2018 at 12:37:08PM +0200, Borislav Petkov wrote:
> Vitezslav reported a case where the
> 
>   "Timeout during microcode update!"
> 
> panic would hit. After a deeper look, it turned out that his .config had
> CONFIG_HOTPLUG_CPU disabled which practically made save_mc_for_early() a
> no-op.
> 
> When that happened, the discovered microcode patch wasn't saved into our
> cache and the late loading path wouldn't find any.
> 
> This, then, lead to early exit from __reload_late() and thus CPUs
> waiting until the timeout is reached, leading to the panic.
> 
> In hindsight, I should've made that function not return before the
> post-synchronization. Oh well, I know better now...
> 
> Reported-by: Vitezslav Samel <vitezslav@...el.cz>
> Signed-off-by: Borislav Petkov <bp@...e.de>

Tested-by: Ashok Raj <ashok.raj@...el.com>

> Cc: Ashok Raj <ashok.raj@...el.com>
> Cc: <stable@...r.kernel.org>
> Fixes: bb8c13d61a62 ("x86/microcode: Fix CPU synchronization routine")
> Link: http://lkml.kernel.org/r/20180418081140.GA2439@pc11.op.pod.cz
> ---