From: Xishi Qiu <qiuxishi@huawei.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: alan@lxorguk.ukuu.org.uk, Linux MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: a question about protection_map[]
Date: Tue, 12 Jul 2016 09:31:30 +0800 [thread overview]
Message-ID: <57844872.1060806@huawei.com> (raw)
In-Reply-To: <20160711133015.GA8028@node.shutemov.name>
On 2016/7/11 21:30, Kirill A. Shutemov wrote:
> On Mon, Jul 11, 2016 at 06:12:30PM +0800, Xishi Qiu wrote:
>> Hi,
>>
>> We can use mprotect to set read only or read/write.
>>
>> mprotect_fixup()
>> vma_set_page_prot()
>> vm_pgprot_modify()
>> vm_get_page_prot()
>> protection_map[vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]
>>
>> The following code shows that prots from __P001(PROT_READ) and __P010(PROT_WRITE)
>> are the same, so how does it distinguish read only or read/write from mprotect?
>
> It doesn't.
>
> Write protection will be removed by fault handler on next write access to
> the page. Somewhat suboptiomal, but zero page implemenation relies on this
> to work properly.
>
Hi Kirill,
I know, PAGE_READONLY and PAGE_COPY are both missed _PAGE_RW,
so it will cause page fault, then we will set new prot flag from
vma, right?
Thanks,
Xishi Qiu
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next prev parent reply other threads:[~2016-07-12 1:34 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-11 10:12 a question about protection_map[] Xishi Qiu
2016-07-11 13:30 ` Kirill A. Shutemov
2016-07-12 1:31 ` Xishi Qiu [this message]
2016-07-12 1:46 ` Kirill A. Shutemov
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