linux-kernel - Re: [PATCH V6 00/26] mm/mmap: Drop __SXXX/_

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Date:   Wed, 6 Jul 2022 11:27:59 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     linux-mm@...ck.org, akpm@...ux-foundation.org
Cc:     hch@...radead.org, christophe.leroy@...roup.eu,
        linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org,
        x86@...nel.org, openrisc@...ts.librecores.org,
        linux-xtensa@...ux-xtensa.org, linux-csky@...r.kernel.org,
        linux-hexagon@...r.kernel.org, linux-parisc@...r.kernel.org,
        linux-alpha@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-um@...ts.infradead.org,
        linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V6 00/26] mm/mmap: Drop __SXXX/__PXXX macros from across
 platforms



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.

- Anshuman