linux-kernel - Re: [PATCH] x86: adjust generic_get

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Message-Id: <500FC1AE020000780009059E@nat28.tlf.novell.com>
Date:	Wed, 25 Jul 2012 08:51:42 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Yinghai Lu" <yinghai@...nel.org>
Cc:	<mingo@...e.hu>, <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>, <hpa@...or.com>
Subject: Re: [PATCH] x86: adjust generic_get_mtrr() for 64-bit

>>> On 06.07.12 at 23:38, Yinghai Lu <yinghai@...nel.org> wrote:
> On Fri, Jul 6, 2012 at 7:14 AM, Jan Beulich <JBeulich@...e.com> wrote:
>> Needing to deal with potentially large memory configurations, the
>> variables here should be "unsigned long" instead of "unsigned int".
>>
>> Signed-off-by: Jan Beulich <jbeulich@...e.com>
>>
>> ---
>>  arch/x86/kernel/cpu/mtrr/generic.c |    8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> --- 3.5-rc5/arch/x86/kernel/cpu/mtrr/generic.c
>> +++ 3.5-rc5-x86-mtrr-generic-types/arch/x86/kernel/cpu/mtrr/generic.c
>> @@ -514,8 +514,8 @@ generic_get_free_region(unsigned long ba
>>  static void generic_get_mtrr(unsigned int reg, unsigned long *base,
>>                              unsigned long *size, mtrr_type *type)
>>  {
>> -       unsigned int mask_lo, mask_hi, base_lo, base_hi;
>> -       unsigned int tmp, hi;
>> +       unsigned long mask_lo, mask_hi, base_lo, base_hi, tmp;
>> +       unsigned int hi;
> 
> _lo, _hi means we want it as 32bit.
> 
> or we just change them to u32 to make it more clear ?

Actually, as I was about to do the adjustment, this isn't correct:
Both mask_hi and base_hi get shifted left in some calculations
there, and hence they would require up-casts to unsigned long
if their type would remain a 32-bit one. Further, mask_lo gets
or-ed with size_or_mask, which is u64, the result compared
with tmp (now unsigned long), and the same result also negated
so the *size (also unsigned long), so needs to be unsigned long
itself unless we want to introduce another variable.

That leaves only base_lo as a candidate for remaining 32-bit,
but for consistency I think it would be better to have them all
have the same type.

Consequently I think the patch should remain as is.

Jan

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