[Question] A question about arm64 pte

[Yisheng Xie]

On 2017/1/17 19:45, Catalin Marinas wrote:
> On Tue, Jan 17, 2017 at 11:53:43AM +0800, Yisheng Xie wrote:
>> On 2017/1/16 22:36, Catalin Marinas wrote:
>>> On Mon, Jan 16, 2017 at 08:39:56PM +0800, Yisheng Xie wrote:
>>>> On 2017/1/16 19:56, Catalin Marinas wrote:
>>>>> On Mon, Jan 16, 2017 at 06:08:47PM +0800, Yisheng Xie wrote:
>>>>>
>>
>> Here is what I get when mmap a reserved memory region 0x39ef 0000~0x3a00 0000
>> use /dev/mem:
>> [  442.704228] pgd = ffff802785f14000
>> [  442.707641] [ffff86e4b000] *pgd=000000279080c003, *pud=0000002785f01003, *pmd=0000002783f5b003, *pte=0168000039ef0fd3
> 
> The pte seems to have bit 7 set: PTE_RDONLY. So you would get a fault on
> write (but not read). Since PTE_WRITE is also set, handle_pte_fault()
> will mark the entry as dirty (bit 55, cleared above) and clear
> PTE_RDONLY before restarting the access instruction. User space wouldn't
> notice, just a slight delay on the first access.
> 
Hi Catalin,
Really thank you for kindly explain, quite clear now.

Thanks
Yisheng Xie.