linux-kernel - Re: [PATCH v2 08/14] x86/fault: Skip erratum #93 workaround on new CPUs

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Message-ID: <CALCETrXYBSsgqe4ANqZWWC6ziuoWT6KPLOz+ZCCVGGG5qWjO3Q@mail.gmail.com>
Date:   Wed, 10 Feb 2021 08:09:45 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Yonghong Song <yhs@...com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v2 08/14] x86/fault: Skip erratum #93 workaround on new CPUs

On Wed, Feb 10, 2021 at 5:29 AM Borislav Petkov <bp@...en8.de> wrote:
>
> On Tue, Feb 09, 2021 at 10:06:02PM -0800, Andy Lutomirski wrote:
> > On Tue, Feb 9, 2021 at 6:33 PM Andy Lutomirski <luto@...nel.org> wrote:
> > >
> > > Erratum #93 applies to the first generation of AMD K8 CPUs.  Skip the
> > > workaround on newer CPUs.
> >
> > Whoops, this breaks the !CPU_SUP_AMD build.  It needs a fixup like this:
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/fault&id=06772a3b6918bf6d6d0778946149b7d56ae30d80
> >
> > Boris, do you want a v3?
>
> Do we even want to apply patch 8 at all? This has always ran on K8 NPT
> CPUs too and those are pretty much obsolete by now so I'm thinking,
> leave sleeping dogs lie...?

I think we do want this patch.  Without it, there's a fairly sizeable
range of bogus RIP values that will result in applying the fixup
instead of properly oopsing, even on new CPUs.