Re: [PATCH 1/3] mm: introduce VM_MAYBE_GUARD and make visible for guard regions

[Lorenzo Stoakes]

On Fri, Oct 31, 2025 at 04:12:51PM -0700, Suren Baghdasaryan wrote:
>
> Overall, I think it should be possible to set this flag atomically
> under VMA read-lock. However, if you introduce new vm_flags
> manipulation functions, please make sure they can't be used for other
> vm_flags. In Android I've seen several "interesting" attempts to
> update vm_flags under a read-lock (specifically in the page-fault
> path) and had to explain why that's a bad idea.

Yeah agreed, so the idea would be to absolutely ring-fence any flag we do
this with entirely. Probably a VM_WARN_ON_ONCE() for anybody trying it with
other flags so bots can catch anybody being naughty.

That kind of 'interesting' stuff is another reason I prefer to really limit
what drivers can do btw ;)

Will have a respin with this idea applied relatively soon hopefully.

Cheers, Lorenzo