linux-kernel - Re: [PATCH] x86: x86_{phys,virt}

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Date:	Thu, 18 Sep 2008 16:52:20 +0100
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>, <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: x86_{phys,virt}_bits field also for i386 (v3)

>>> "H. Peter Anvin" <hpa@...or.com> 18.09.08 17:25 >>>
>Jan Beulich wrote:
>> +
>> +#ifdef CONFIG_X86_32
>> +	if (cpu_has(c, X86_FEATURE_PAE) || cpu_has(c, X86_FEATURE_PSE36))
>> +		c->x86_phys_bits = 36;
>> +#endif
>>  }
>>  
>
>I'm confused about this.
>
>There is no reason for this to be #ifdef'd; but it should be conditional 
>on this information not being otherwise available (which will always be 
>the case on 64 bits), I would assume.  If we are setting a value there, 
>we should presumably also set 32 in the other case.

It does get set to 32 first (and only for 32-bits - 64bits didn't set any
default so far, so I didn't want to make it to now), and the code fragment
above updates that default after feature flags have been obtained, but
before other capabilities (including the phys/virt bit widths) are being
gathered.

Jan

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