Re: [PATCH V6 00/26] mm/mmap: Drop __SXXX/__PXXX macros from across platforms

Christophe Leroy
2022-07-06T06:34:03Z

Le 06/07/2022 à 07:57, Anshuman Khandual a écrit :
>
>
> On 6/30/22 10:46, Anshuman Khandual wrote:
>> __SXXX/__PXXX macros is an unnecessary abstraction layer in creating the
>> generic protection_map[] array which is used for vm_get_page_prot(). This
>> abstraction layer can be avoided, if the platforms just define the array
>> protection_map[] for all possible vm_flags access permission combinations
>> and also export vm_get_page_prot() implementation.
>>
>> This series drops __SXXX/__PXXX macros from across platforms in the tree.
>> First it build protects generic protection_map[] array with '#ifdef __P000'
>> and moves it inside platforms which enable ARCH_HAS_VM_GET_PAGE_PROT. Later
>> this build protects same array with '#ifdef ARCH_HAS_VM_GET_PAGE_PROT' and
>> moves inside remaining platforms while enabling ARCH_HAS_VM_GET_PAGE_PROT.
>> This adds a new macro DECLARE_VM_GET_PAGE_PROT defining the current generic
>> vm_get_page_prot(), in order for it to be reused on platforms that do not
>> require custom implementation. Finally, ARCH_HAS_VM_GET_PAGE_PROT can just
>> be dropped, as all platforms now define and export vm_get_page_prot(), via
>> looking up a private and static protection_map[] array. protection_map[]
>> data type has been changed as 'static const' on all platforms that do not
>> change it during boot.
>>
>> This series applies on v5.19-rc4 and has been build tested for multiple
>> platforms. While here it has dropped off all previous tags from folks after
>> the current restructuring. Series common CC list has been expanded to cover
>> all impacted platforms for wider reach.
>>
>> - Anshuman
>>
>> Changes in V6:
>>
>> - Converted protection_map[] array as 'static const' on sparc32 platform
>> - Rebased on v5.19-rc4
>> - Collected tags
>
> There are two linux-next based build fixes for this series (listed below), when
> vm_get_page_prot() gets redefined with !CONFIG_MMU. Platform vm_get_page_prot()
> is required only with CONFIG_MMU enabled, otherwise there is a generic fallback
> stub in include/linux/mm.h
>
> https://lore.kernel.org/all/20220705221411.3381797-1-jcmvbkbc@gmail.com/ [xtensa]
> https://lore.kernel.org/all/20220706054002.1936820-1-anshuman.khandual@arm.com/ [sh]
>
> It does not seem CONFIG_MMU can be disabled on other platforms thus exposing a build
> failure. But just to be on the safer side, should all vm_get_page_prot() be wrapped
> around with #ifdef CONFIG_MMU ? In that case will resend the series with above build
> fixes folded back in as well. Please do suggest. Thank you.
>

As far as I can see in Kconfig, CONFIG_MMU is user selectable on the
following architectures:
- ARM
- M68K
- RISCV
- SH

And is disabled by default on XTENSA.

So I guess ARM, M68K, RISCV, SH and XTENSA should have it wrapped around
#ifdef CONFIG_MMU , or have it in a file that is not built when
CONFIG_MMU is not set.

Christophe