Re: [PATCH 0/2] page_count can't be used to decide when wp_page_copy

[Jason Gunthorpe]

On Thu, Jan 07, 2021 at 03:04:00PM -0500, Andrea Arcangeli wrote:

> vmsplice syscall API is insecure allowing long term GUP PINs without
> privilege.

Lots of places are relying on pin_user_pages long term pins of memory,
and cannot be converted to notifiers.

I don't think it is reasonable to just declare that insecure and
requires privileges, it is a huge ABI break.

FWIW, vhost tries to use notifiers as a replacement for GUP, and I
think it ended up quite strange and complicated. It is hard to
maintain performance when every access to the pages needs to hold some
protection against parallel invalidation.

Jason