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SubjectRe: [PATCH] x86/mm: fix regression with huge pages on PAE
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On 11/12/2015 04:00 AM, Kirill A. Shutemov wrote:
> On Thu, Nov 12, 2015 at 09:54:18AM +0100, Ingo Molnar wrote:
>> * Kirill A. Shutemov <kirill.shutemov@linux.intel.com> wrote:
>>
>>> diff --git a/arch/x86/include/asm/page_types.h b/arch/x86/include/asm/page_types.h
>>> index c5b7fb2774d0..cc071c6f7d4d 100644
>>> --- a/arch/x86/include/asm/page_types.h
>>> +++ b/arch/x86/include/asm/page_types.h


Kirill, where are we with this patch?

-boris

>>> @@ -9,19 +9,21 @@
>>> #define PAGE_SIZE (_AC(1,UL) << PAGE_SHIFT)
>>> #define PAGE_MASK (~(PAGE_SIZE-1))
>>>
>>> +#define PMD_PAGE_SIZE (_AC(1, UL) << PMD_SHIFT)
>>> +#define PMD_PAGE_MASK (~(PMD_PAGE_SIZE-1))
>>> +
>>> +#define PUD_PAGE_SIZE (_AC(1, UL) << PUD_SHIFT)
>>> +#define PUD_PAGE_MASK (~(PUD_PAGE_SIZE-1))
>>> +
>>> #define __PHYSICAL_MASK ((phys_addr_t)((1ULL << __PHYSICAL_MASK_SHIFT) - 1))
>>> #define __VIRTUAL_MASK ((1UL << __VIRTUAL_MASK_SHIFT) - 1)
>>>
>>> -/* Cast PAGE_MASK to a signed type so that it is sign-extended if
>>> +/* Cast *PAGE_MASK to a signed type so that it is sign-extended if
>>> virtual addresses are 32-bits but physical addresses are larger
>>> (ie, 32-bit PAE). */
>>> #define PHYSICAL_PAGE_MASK (((signed long)PAGE_MASK) & __PHYSICAL_MASK)
>>> -
>>> -#define PMD_PAGE_SIZE (_AC(1, UL) << PMD_SHIFT)
>>> -#define PMD_PAGE_MASK (~(PMD_PAGE_SIZE-1))
>>> -
>>> -#define PUD_PAGE_SIZE (_AC(1, UL) << PUD_SHIFT)
>>> -#define PUD_PAGE_MASK (~(PUD_PAGE_SIZE-1))
>>> +#define PHYSICAL_PMD_PAGE_MASK (((signed long)PMD_PAGE_MASK) & __PHYSICAL_MASK)
>>> +#define PHYSICAL_PUD_PAGE_MASK (((signed long)PUD_PAGE_MASK) & __PHYSICAL_MASK)
>> that's a really odd way of writing it, 'long' is signed by default ...
> See the comment above (it was there before the patch). 'signed' can be
> considered as documentation -- we want sign-extension here.
>
>> There seems to be 150+ such cases in the kernel source though - weird.
>>
>> More importantly, how does this improve things on 32-bit PAE kernels? If I follow
>> the values correctly then PMD_PAGE_MASK is 'UL' i.e. 32-bit:
>>
>>> +#define PMD_PAGE_SIZE (_AC(1, UL) << PMD_SHIFT)
>>> +#define PMD_PAGE_MASK (~(PMD_PAGE_SIZE-1))
>> thus PHYSICAL_PMD_PAGE_MASK is 32-bit too:
>>
>>> +#define PHYSICAL_PMD_PAGE_MASK (((signed long)PMD_PAGE_MASK) & __PHYSICAL_MASK)
>> so how is the bug fixed?
> Again, see the comment.
> I've checked that it generates correct value (using kernel/bounds.c).
>



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