linux-kernel - Re: [PATCH] EDAC/mce_amd: Reduce unnecessary spew in dmesg if SMCA feature bit is not exposed

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Date:   Tue, 15 Jun 2021 11:16:49 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        James Morse <james.morse@....com>,
        "yazen.ghannam@....com" <yazen.ghannam@....com>,
        Robert Richter <rric@...nel.org>
Subject: Re: [PATCH] EDAC/mce_amd: Reduce unnecessary spew in dmesg if SMCA
 feature bit is not exposed

On Mon, Jun 14, 2021 at 10:25:36PM +0000, Luck, Tony wrote:
> I expect all the Intel EDAC drivers that load based on CPU model have similar
> issues. Maybe they aren't whining as loudly about not being able to find the
> memory controller devices?

Right.

> Though perhaps this is an issue outside of EDAC and x86_match_cpu()
> could do the HYPERVISOR check and return no match. The few callers
> who want to believe the fictional CPU model number passed in by the
> VMM would need to use some new variant of the call?

Yeah, we could do

X86_MATCH_VENDOR_FAM_MODEL_STEPPINGS_NOT_FEATURE

notice the "NOT" and have a x86_cpu_id.not_feature which to match
X86_FEATURE_HYPERVISOR. I'm not sure it is worth it, though, for a
handful of drivers.

The whole thing is a meh, why bother, but I got tired of this particular
intent of people wanting to shut this error message up just because they
should not load that driver in a VM in the first place.

But what happens is they boot a guest with -cpu host and in that case
that's a new CPU - family 0x19 - so it doesn't have a case 0x19 for the
pr_warn_once() there.

And instead of keep adding adding families there, I'd simply check
X86_FEATURE_HYPERVISOR.

Oh and that thing - mce_amd.c - doesn't use x86_match_cpu() so it has to
be an explicit check on function entry.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette