linux-kernel - Re: [Patch V1 2/7] x86/microcode/intel: Remove retries on early microcode load

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Date:   Fri, 02 Dec 2022 20:01:54 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ashok Raj <ashok.raj@...el.com>, Borislav Petkov <bp@...en8.de>
Cc:     X86-kernel <x86@...nel.org>,
        LKML Mailing List <linux-kernel@...r.kernel.org>,
        Ashok Raj <ashok.raj@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>, alison.schofield@...el.com,
        reinette.chatre@...el.com
Subject: Re: [Patch V1 2/7] x86/microcode/intel: Remove retries on early
 microcode load

On Tue, Nov 29 2022 at 13:08, Ashok Raj wrote:
> Microcode loading can fail. This happens today when handling mixed
> steppings. But it can also happen for other reasons such as corrupted
> image, Security Version Number (SVN) preventing anti-rollback,
> dependencies on BIOS loaded microcode image for some capabilities.
>
> When the microcode loading fails, the kernel will quietly hang at boot.
> This has been observed by end users (Links below) who had to revert their
> microcode packages in order to boot again.
>
> The hang is due to an infinite retry loop. The retries were in place to
> support systems with mixed steppings. Now that mixed steppings are no
> longer supported, there is only one microcode image at a time. Any retries
> will simply reattempt to apply the same image over and over without making
> progress.
>
> Some possible past bugs that could be due to this bug are below.
>
> There is no direct evidence that these end user issues were caused by this
> retry loop. However, the early boot hangs along with reverting the
> microcode update workaround provide strong circumstantial evidence to
> support the theory that they are linked.
>
> Remove the retry loop and only attempt to apply microcode once.

Very concise and informative changelog. See, you can do it :)

> Link: https://bugs.launchpad.net/ubuntu/+source/intel-microcode/+bug/1911959
> Link: https://forums.linuxmint.com/viewtopic.php?p=1827032#1827032
> Link: https://askubuntu.com/questions/1291486/boot-crash-after-latest-update-of-intel-microcode-nov-11-2020
> Fixes: 06b8534cb728 ("x86/microcode: Rework microcode loading")
> Cc: stable@...r.kernel.org
> Signed-off-by: Ashok Raj <ashok.raj@...el.com>

Nit: Can you order the tags according to the tip documentation next time
     please?

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>