Re: [Xen-devel] [PATCH v5 02/12] arm/mem_access: Move PAGE_SHIFT_* macros to lib.h

[Sergej Proskurin <proskurin@xxxxxxxxxxxxx>]

Hi Jan,


On 07/03/2017 11:16 AM, Jan Beulich wrote:
>>>> On 03.07.17 at 11:03, <proskurin@xxxxxxxxxxxxx> wrote:
>> To prevent potential type width issues with ARMv7, I would reuse the
>> macro from xen/iommu.h at this point:
>>
>> PAGE_MASK_GRAN(sz)                     (~(u64)0 << PAGE_SHIFT_##sz)
> Seems reasonable, except
> - no new use of u64 please (use uint64_t instead)
> - it's questionable whether a 64-bit type here is correct in the
>   first place, especially when considering 32-bit architectures

As to prevent breaking the currently available implementation making use
of the existing defines in xen/iommu.h, I believe the PAGE_MASK_GRAN(sz)
macro should keep the type of uint64_t. Additonally, the introduced
PAGE_*_GRAN(sz) macros might be applied in the context of the
long-descriptor translation table format with 64bit PTEs for both ARMv8
and ARMv7. Having an unsigned long at this point would limit the mask to
32 bit on ARMv7 and thus not be appropriate in handling the
long-descriptor format on ARMv7. Please let me know if you still think
that using the uint64_t at this point is still questionable.

Apart from that, I discovered that there is no code that currently uses
PAGE_{SIZE,MASK.ALIGN}_64*K. The only 64-bit related macro in use is
PAGE_SHIFT_64K. So I wonder whether we need these defines after all (the
same would apply to 16K as well)?

Thanks you,
~Sergej


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