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

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Message-ID: <53A46365.6090101@zytor.com>
Date:	Fri, 20 Jun 2014 09:37:57 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Dave Hansen <dave@...1.net>, linux-kernel@...r.kernel.org
CC:	bp@...en8.de, 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 06/20/2014 09:30 AM, Dave Hansen wrote:
> On 06/20/2014 09:23 AM, H. Peter Anvin wrote:
>> On 06/20/2014 09:17 AM, Dave Hansen wrote:
>>>> Today, we assume that all 64-bit cpus have X86_FEATURE_MP.  It
>>>> should be in the REQUIRED_MASK so that we do not need the #undef
>>>> trick for it.
>> I don't think we enforce that the MP bit is set in CPUID, though.
>> Non-AMD processors will typically not set this bit at all, so the
>> feature validation code would have to be modified to know to not require
>> this bit.
> 
> Ahh, OK.  I'll drop this.
> 

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?

	-hpa


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