linux-kernel - Re: [PATCH] x86/amd: Work around Erratum 1386

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Message-ID: <ee866b3e-a53b-4c26-0272-20e798c0650d@citrix.com>
Date:   Tue, 7 Mar 2023 20:01:36 +0000
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Tavis Ormandy <taviso@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Alexander Monakov <amonakov@...ras.ru>
Subject: Re: [PATCH] x86/amd: Work around Erratum 1386 - XSAVES malfunction on
 context switch

On 07/03/2023 6:56 pm, Borislav Petkov wrote:
> On Tue, Mar 07, 2023 at 06:22:01PM +0000, Andrew Cooper wrote:
>> Well yes - more and more reports of impacted systems.
>>
>> Having the full list of affected models is great and all, but how is it
>> going to change this patch as a workaround ?
> We don't have to clear the feature flag on those systems which have
> a fix.

Sure, but why is that helpful?

XSAVES and XSAVEC are functionally identical on Zen1/2 because these
CPUs don't advertise any supervisor XSAVE states.

It is only Zen3 where XSAVES starts doing more than XSAVEC (and even
then, only after the CET series actually gets merged...)

~Andrew