# Re: \[PATCH v21 10/26\] x86/mm: Update pte\_modify for \_PAGE\_COW

- From: Yu, Yu-cheng \<hidden\>
- Date: 2021-03-08 16:52:37 
- List: linux-doc
- Page: https://ratatoskr.run/linux-doc/2021/03/6292477
- Thread: https://ratatoskr.run/linux-doc/2021/02/6272416/t.md

```text
On 3/5/2021 6:29 AM, Borislav Petkov wrote:
> On Wed, Feb 17, 2021 at 02:27:14PM -0800, Yu-cheng Yu wrote:
>> @@ -787,16 +802,34 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
>>   	 */
>>   	val &= _PAGE_CHG_MASK;
>>   	val |= check_pgprot(newprot) & ~_PAGE_CHG_MASK;
>> +	val = fixup_dirty_pte(val);
>
> Do I see it correctly that you can do here and below:
>
> 	/*
> 	 * Fix up potential shadow stack page flags because the RO, Dirty PTE is
> 	 * special.
> 	 */
> 	if (pte_dirty()) {
> 		pte_mkclean();
> 		pte_mkdirty();
> 	}
>
> ?

Yes, this looks better.  Thanks!

>
> That fixup thing looks grafted and not like a normal flow to me.
>

```