Re: [RFC 2/3] mm/vma: Introduce VM_ACCESS_FLAGS

[Anshuman Khandual]

On 03/03/2020 11:18 PM, Vlastimil Babka wrote:
> On 3/2/20 7:47 AM, Anshuman Khandual wrote:
>> There are many places where all basic VMA access flags (read, write, exec)
>> are initialized or checked against as a group. One such example is during
>> page fault. Existing vma_is_accessible() wrapper already creates the notion
>> of VMA accessibility as a group access permissions. Hence lets just create
>> VM_ACCESS_FLAGS (VM_READ|VM_WRITE|VM_EXEC) which will not only reduce code
>> duplication but also extend the VMA accessibility concept in general.
>>
>> Cc: Russell King <linux@xxxxxxxxxxxxxxx>
>> CC: Catalin Marinas <catalin.marinas@xxxxxxx>
>> CC: Mark Salter <msalter@xxxxxxxxxx>
>> Cc: Nick Hu <nickhu@xxxxxxxxxxxxx>
>> CC: Ley Foon Tan <ley.foon.tan@xxxxxxxxx>
>> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
>> Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
>> Cc: Yoshinori Sato <ysato@xxxxxxxxxxxxxxxxxxxx>
>> Cc: Guan Xuetao <gxt@xxxxxxxxxx>
>> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
>> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>> Cc: Rob Springer <rspringer@xxxxxxxxxx>
>> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
>> Cc: linux-c6x-dev@xxxxxxxxxxxxx
>> Cc: nios2-dev@xxxxxxxxxxxxxxxxxxxxxx
>> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
>> Cc: linux-s390@xxxxxxxxxxxxxxx
>> Cc: linux-sh@xxxxxxxxxxxxxxx
>> Cc: devel@xxxxxxxxxxxxxxxxxxxx
>> Cc: linux-mm@xxxxxxxxx
>> Cc: linux-kernel@xxxxxxxxxxxxxxx
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> 
> Dunno. Such mask seems ok for testing flags, but it's a bit awkward when
> initializing flags, where it covers just one of many combinations that seem
> used. But no strong opinions, patch looks correct.

Fair enough. The fact that it covers only one of the many init combinations
used at various places, is indeed a good point. The page fault handlers does
start with VMA flags mask as VM_ACCESS_FLAGS, hence will keep them and drop
other init cases here.