linux-kernel - Re: [RFC][PATCH 3/3] x86: make MP a required-feature on 64-bit

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Message-ID: <20140620174345.GD11391@pd.tnic>
Date:	Fri, 20 Jun 2014 19:43:45 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Dave Hansen <dave@...1.net>, linux-kernel@...r.kernel.org,
	x86@...nel.org, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [RFC][PATCH 3/3] x86: make MP  a required-feature on 64-bit

On Fri, Jun 20, 2014 at 09:37:57AM -0700, H. Peter Anvin wrote:
> We probably should just the cpu_has_mp macro entirely.  All it is used
> for is printing a warning in amd_k7_smp_check().
> 
> Andi, Borislav -- as far as I can tell, we have *never* enforced this on
> the 64-bit kernel, although we have enforced it on 64-bit processors
> running the 32-bit kernel.  We should either enforce it on both or just
> drop it.  What is your opinion?

Well, my AMD CPUID guide says CPUID Fn8000_0001_EDX[19] is reserved,
i.e. that X86_FEATURE_MP bit will be probably cleared.

And so it is, on my F15h AMD it is not set:

eax in: 0x80000001, eax = 00600f20 ebx = 10000000 ecx = 01ebbfff edx = 2fd3fbff
									  ^
								----------|

So I don't think we should enforce it on 64-bit.

I guess we can leave the check in amd_k7_smp_check() though but remove that
nasty cpu_has_mp macro and do static_cpu_has() instead.

My 2¢ only.

-- 
Regards/Gruss,
    Boris.

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