linux-kernel - Re: [PATCH 01/11] x86/fault: Fix AMD erratum #91 errata fixup for user code

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Date:   Mon, 1 Feb 2021 10:05:59 +0100
From:   Christoph Hellwig <hch@....de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     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>, stable@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 01/11] x86/fault: Fix AMD erratum #91 errata fixup for
 user code

On Sun, Jan 31, 2021 at 09:24:32AM -0800, Andy Lutomirski wrote:
> While we're at it, disable the workaround on all CPUs except AMD Family
> 0xF.  By my reading of the Revision Guide for AMD Athlon™ 64 and AMD
> Opteron™ Processors, only family 0xF is affected.

I think it would be better to have one no risk refression fix that
just probes both user and kernel addresses and a separate one to
restrict the workaround.

> +	if (likely(boot_cpu_data.x86_vendor != X86_VENDOR_AMD
> +		   || boot_cpu_data.x86 != 0xf))

Normally kernel style would be to have the || on the first line.