Re: [PATCH 1/6] mm: enable page walking API to lock vmas during the walk

[Suren Baghdasaryan]

On Mon, Jul 31, 2023 at 1:24 PM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:
>
> On Mon, Jul 31, 2023 at 12:33 PM Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > On Mon, 31 Jul 2023 at 12:31, Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:
> > >
> > > I got the idea but a couple of modifications, if I may.
> >
> > Ack, sounds sane to me.
>
> Ok, I'll wait for more feedback today and will post an update tomorrow. Thanks!

I have the new patchset ready but I see 3 places where we walk the
pages after mmap_write_lock() while *I think* we can tolerate
concurrent page faults (don't need to lock the vmas):

s390_enable_sie()
break_ksm()
clear_refs_write()

In all these walks we lock PTL when modifying the page table entries,
that's why I think we can skip locking the vma but maybe I'm missing
something? Could someone please check these 3 cases and confirm or
deny my claim?
Thanks,
Suren.

>
> >
> >              Linus