From mboxrd@z Thu Jan  1 00:00:00 1970
From: xieyisheng1@huawei.com (Yisheng Xie)
Date: Mon, 16 Jan 2017 20:39:56 +0800
Subject: [Question] A question about arm64 pte
In-Reply-To: <20170116115606.GA6832@e104818-lin.cambridge.arm.com>
References: <d284f510-f025-db84-f21e-a5b167d4bcd2@huawei.com>
 <20170116115606.GA6832@e104818-lin.cambridge.arm.com>
Message-ID: <6b7a9bd2-37af-40cd-b723-9e648fbbc7c8@huawei.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

hi Catalin,
Thank you so much for you reply.

On 2017/1/16 19:56, Catalin Marinas wrote:
> On Mon, Jan 16, 2017 at 06:08:47PM +0800, Yisheng Xie wrote:
>> I have question about arm64 pte.
> 
> I assume the context is ARMv8.0 (without hardware DBM support).

Yes.
> 
>> For arm64, PTE_WRITE?== PTE_DBM? is to mark whether the page is writable,
>> and PTE_DIRTY is to mark whether the page is dirty.
>> However, PTE_RDONLY is only cleared when both PTE_WRITE and PTE_DIRTY are set.
> 
> That's what set_pte_at() does.
> 

So if we mmap a memory region use /dev/mem like:
   fildes = open("/dev/mem", O_RDWR | O_CREAT, 0777);
   addr = mmap(NULL, LEN, PROT_READ | PROT_WRITE, MAP_SHARED, fildes, offset);

The PTE_RDONLY will be set? Right ?
However?when use memset to write the region it still works well, and the bit PTE_RDONLY is also cleared.
Is there anywhere clear the PTE_RDONLY before write that page ?

Thanks
Yisheng Xie