[Question] A question about arm64 pte

[Yisheng Xie]

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