linux-kernel - Re: x86: AMD Zen2 ymm registers rolling back

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Message-ID: <Y/aIjUr78yd9U+wl@thinkstation.cmpxchg8b.net>
Date:   Wed, 22 Feb 2023 13:26:37 -0800
From:   Tavis Ormandy <taviso@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Andrew Cooper <andrew.cooper3@...rix.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: x86: AMD Zen2 ymm registers rolling back

On Wed, Feb 22, 2023 at 11:09:51AM +0100, Borislav Petkov wrote:
> On Wed, Feb 22, 2023 at 09:38:09AM +0000, Andrew Cooper wrote:
> > This sounds suspiciously like an errata which was fixed with a ucode
> > update last year.
> 
> Yes, it looks like it.
> 
> Alternatively, you can try booting with "clearcpuid=xsaves" - that
> should take care of your observation too but yeah, you should rather
> update your microcode.
> 

Thanks - confirmed, it *doesn't* repro with 0x8301055, but does repro
with 0x830104d.

Annoyingly, I thought I was using the most recent microcode, but it seems
like there is some bug and debian wasn't applying it at boot.

That seems like a scary errata :-/

Tavis.

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