Messages in this thread | | | Date | Tue, 25 Apr 2023 00:26:25 +0100 | From | Lorenzo Stoakes <> | Subject | Re: [PATCH v2] mm/gup: disallow GUP writing to file-backed mappings by default |
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On Mon, Apr 24, 2023 at 08:17:11PM -0300, Jason Gunthorpe wrote: > On Tue, Apr 25, 2023 at 12:03:34AM +0100, Lorenzo Stoakes wrote: > > > Except you dirty a page that is mapped elsewhere that thought everything > > was cleaned and... not sure the PTLs really help you much? > > If we have a writable PTE then while the PTE's PTL is held it is impossible > for a FS to make the page clean as any cleaning action has to also > take the PTL to make the PTE non-present or non-writable. >
That's a very good point! Passing things back with a spinlock held feels pretty icky though, and obviously a no-go for a FOLL_PIN. Perhaps for a FOLL_GET this would be workable.
> > If we want to be more adventerous the opt-in variant could default to on > > for FOLL_LONGTERM too, but that discussion can be had over on that patch > > series. > > I think you should at least do this too to explain why io_uring code > is moving into common code.. >
OK, I'll respin this as a v3 of this series then since we'll be defaulting FOLL_LONGTERM at least (for which there seems to be broad consensus), but also permit this flag to be set manually and set it for io_uring.
> Jason
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