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Subject: Re: [RFC 2/3] mm/vma: Introduce VM_ACCESS_FLAGS
To:     Vlastimil Babka <vbabka@suse.cz>, linux-mm@kvack.org
Cc:     Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Mark Salter <msalter@redhat.com>,
        Nick Hu <nickhu@andestech.com>,
        Ley Foon Tan <ley.foon.tan@intel.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Guan Xuetao <gxt@pku.edu.cn>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Rob Springer <rspringer@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-arm-kernel@lists.infradead.org, linux-c6x-dev@linux-c6x.org,
        nios2-dev@lists.rocketboards.org, linuxppc-dev@lists.ozlabs.org,
        linux-s390@vger.kernel.org, linux-sh@vger.kernel.org,
        devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org
References: <1583131666-15531-1-git-send-email-anshuman.khandual@arm.com>
 <1583131666-15531-3-git-send-email-anshuman.khandual@arm.com>
 <52b4565f-2dab-c3e5-ead8-d76258f43a10@suse.cz>
From:   Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <d00c5b01-fb69-3a83-3eae-36231c5b08e9@arm.com>
Date:   Wed, 4 Mar 2020 11:22:46 +0530
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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@armlinux.org.uk>
>> CC: Catalin Marinas <catalin.marinas@arm.com>
>> CC: Mark Salter <msalter@redhat.com>
>> Cc: Nick Hu <nickhu@andestech.com>
>> CC: Ley Foon Tan <ley.foon.tan@intel.com>
>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>> Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
>> Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
>> Cc: Guan Xuetao <gxt@pku.edu.cn>
>> Cc: Dave Hansen <dave.hansen@linux.intel.com>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Rob Springer <rspringer@google.com>
>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: linux-arm-kernel@lists.infradead.org
>> Cc: linux-c6x-dev@linux-c6x.org
>> Cc: nios2-dev@lists.rocketboards.org
>> Cc: linuxppc-dev@lists.ozlabs.org
>> Cc: linux-s390@vger.kernel.org
>> Cc: linux-sh@vger.kernel.org
>> Cc: devel@driverdev.osuosl.org
>> Cc: linux-mm@kvack.org
>> Cc: linux-kernel@vger.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> 
> 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.