On 4/16/26 15:49, Kiryl Shutsemau wrote: > On Tue, Apr 14, 2026 at 06:10:44PM +0100, Kiryl Shutsemau wrote: >> On Tue, Apr 14, 2026 at 05:37:50PM +0200, David Hildenbrand (Arm) wrote: >>> >>> I would rather tackle this from the other direction: it's another form >>> of protection (like WP), not really a "minor" mode. >>> >>> Could we add a UFFDIO_REGISTER_MODE_RWP (or however we would call it) >>> and support it for anon+shmem, avoiding the zapping for shmem completely? >> >> I like this idea. >> >> It should be functionally equivalent, but your interface idea fits >> better with the rest. >> >> Thanks! Will give it a try. > > Here is an updated version: > > https://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git/log/?h=uffd/rfc-v2 > > will post after -rc1 is tagged. > > I like it more. It got substantially cleaner.
I don't have time to look into the details just yet, but my thinking was that a) It would avoid the zap+refault b) We could reuse the uffd-wp PTE bit + marker to indicate/remember the protection, making it co-exist with NUMA hinting naturally. b) obviously means that we cannot use uffd-wp and uffd-rwp at the same time in the same uffd area. I guess that should be acceptable for the use cases we you should have in mind? But I also haven't taken a closer look at this patch set, whether you would already be using a PTE bit somehow (I suspect not :) ) -- Cheers, David
