From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Xishi Qiu <qiuxishi@huawei.com>
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 04:46:50 +0300 [thread overview]
Message-ID: <20160712014650.GA18041@node> (raw)
In-Reply-To: <57844872.1060806@huawei.com>
On Tue, Jul 12, 2016 at 09:31:30AM +0800, Xishi Qiu wrote:
> 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?
Yes. See wp_page_reuse().
--
Kirill A. Shutemov
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WARNING: multiple messages have this Message-ID (diff)
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Xishi Qiu <qiuxishi@huawei.com>
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 04:46:50 +0300 [thread overview]
Message-ID: <20160712014650.GA18041@node> (raw)
In-Reply-To: <57844872.1060806@huawei.com>
On Tue, Jul 12, 2016 at 09:31:30AM +0800, Xishi Qiu wrote:
> 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?
Yes. See wp_page_reuse().
--
Kirill A. Shutemov
next prev parent reply other threads:[~2016-07-12 1:46 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-11 10:12 a question about protection_map[] Xishi Qiu
2016-07-11 10:12 ` Xishi Qiu
2016-07-11 13:30 ` Kirill A. Shutemov
2016-07-11 13:30 ` Kirill A. Shutemov
2016-07-12 1:31 ` Xishi Qiu
2016-07-12 1:31 ` Xishi Qiu
2016-07-12 1:46 ` Kirill A. Shutemov [this message]
2016-07-12 1:46 ` Kirill A. Shutemov
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