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

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Date:   Fri, 20 Apr 2018 12:54:38 +0200
From:   Vitezslav Samel <vitezslav@...el.cz>
To:     Borislav Petkov <bp@...e.de>
Cc:     "Raj, Ashok" <ashok.raj@...el.com>,
        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>

  Tested-by: Vitezslav Samel <vitezslav@...el.cz>

> Signed-off-by: Borislav Petkov <bp@...e.de>
> 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
> ---
>  arch/x86/kernel/cpu/microcode/core.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
> index 10c4fc2c91f8..77e201301528 100644
> --- a/arch/x86/kernel/cpu/microcode/core.c
> +++ b/arch/x86/kernel/cpu/microcode/core.c
> @@ -564,14 +564,12 @@ static int __reload_late(void *info)
>  	apply_microcode_local(&err);
>  	spin_unlock(&update_lock);
>  
> +	/* siblings return UCODE_OK because their engine got updated already */
>  	if (err > UCODE_NFOUND) {
>  		pr_warn("Error reloading microcode on CPU %d\n", cpu);
> -		return -1;
> -	/* siblings return UCODE_OK because their engine got updated already */
> +		ret = -1;
>  	} else if (err == UCODE_UPDATED || err == UCODE_OK) {
>  		ret = 1;
> -	} else {
> -		return ret;
>  	}
>  
>  	/*
> -- 
> 2.13.0
> 
> SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
> --