ARM64: Adding write-protect bit for Userfaultfd

[Joey Gouly]

Hi,

On Wed, May 17, 2023 at 11:43:29AM -0400, Mohamed Husain Noor Mohamed wrote:
> Hi Catalin,
> 
> Thanks for the feedback.
> 
> We were able to implement the feature with bits 60 and 61. As you
> mentioned we made it a conditional feature.
> 
> PTE_UFFD_WP -> 60
> PTE_SWP_UFFD_WP -> 61
> 
> We want to submit the patch(pull request) since our research requires
> this feature in the vanilla kernel. Could you please share the steps
> for that?
> 
> Thanks,
> Mohamed
> 

Bits 60-62 will be used by the VMSA 2022 extension called Permission Overlay Extension.
So if this userfaultd wp support is added and uses those bits, it will have to be mutually
exclusive with POE.

Thanks,
Joey