linux-kernel - Re: [qemu64,+smep,+smap] WARNING: CPU: 1 PID: 0 at arch/x86/kernel/cpu/amd.c:220 init

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Message-ID: <20140307222018.GG5255@pd.tnic>
Date:	Fri, 7 Mar 2014 23:20:18 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Dave Jones <davej@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Ingo Molnar <mingo@...nel.org>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [qemu64,+smep,+smap] WARNING: CPU: 1 PID: 0 at
 arch/x86/kernel/cpu/amd.c:220 init_amd()

On Fri, Mar 07, 2014 at 05:06:55PM -0500, Dave Jones wrote:
> Additionally, fam:6 model:6 stepping 3 never existed in the real
> world afaict. I used to keep x86info's stepping db pretty up to date,
> and that only has knowledge of stepping 1 & 2.[*] Modelling qemu on
> something from the real world might be a better idea than inventing
> new special cases.

Yep.

I'm afraid this qemu64 is some migration/machine snapshot model which
they're using by defining a minimal set of feature bits so that
cross-vendor migration can work. WTH do I know - virt. people are crazy
anyway - that's a given. :-P

>  > Oh, and the thing has CPUID_EXT2_LM which is also a WTH moment for me.
>  > Paolo, what's going on here?
> 
> Yeah, this is a mess, there should be no family < 0xf with LM set.

Right.

> [*] It's possible I somehow missed it, or the AMD rev docs never mentioned it
> for some reason, but it seems unlikely.

Yeah, I think the test in the kernel is open above as a precaution in
case newer models appeared:

        if (((c->x86_model == 6) && (c->x86_mask >= 2)) ||

I hardly can imagine, though, if anyone is actually booting recent
kernels on a K7. We might just as well kill this code and not even miss
it.

Btw, and sometimes when digging around, one can get lucky:
http://support.amd.com/TechDocs/23542a.pdf

K6. Ancient history stuff - I feel like I'm in a museum :-P

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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