Re: [PATCH v8 00/17] gfs2: Fix mmap + page fault deadlocks

[Linus Torvalds]

On Wed, Oct 20, 2021 at 6:37 AM Catalin Marinas <catalin.marinas@xxxxxxx> wrote:
>
> The atomic "add zero" trick isn't that simple for MTE since the arm64
> atomic or exclusive instructions run with kernel privileges and
> therefore with the kernel tag checking mode.

Are there any instructions that are useful for "probe_user_write()"
kind of thing? We could always just add that as an arch function, with
a fallback to using the futex "add zero" if the architecture doesn't
need anything special.

Although at least for MTE, I think the solution was to do a regular
read, and that checks the tag, and then we could use the gup machinery
for the writability checks.

                Linus