Re: [PATCH v12 0/4] fix double page fault in cow_user_page for pfn mapping

[Will Deacon]

On Fri, Oct 11, 2019 at 10:09:35PM +0800, Jia He wrote:
> When we tested pmdk unit test vmmalloc_fork TEST1 in arm64 guest, there
> will be a double page fault in __copy_from_user_inatomic of cow_user_page.
> 
> As told by Catalin: "On arm64 without hardware Access Flag, copying from
> user will fail because the pte is old and cannot be marked young. So we
> always end up with zeroed page after fork() + CoW for pfn mappings. we
> don't always have a hardware-managed access flag on arm64."
> 
> -Changes
> v12:
>     refine PATCH 01, remove the !! since C languages can convert unsigned
>     to bool (Catalin)

Thanks. I think it's a bit late to take something like this for 5.4 now,
especially as the current behaviour has always been there. Hopefully
somebody can queue it for 5.5 instead.

Will