On Mon, Nov 2, 2020 at 2:01 PM Jason Gunthorpe <jgg@xxxxxxxx> wrote: > > On Mon, Nov 02, 2020 at 01:56:10PM +0100, Daniel Vetter wrote: > > On Mon, Nov 2, 2020 at 8:29 AM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > > > > > On Fri, Oct 30, 2020 at 11:08:08AM +0100, Daniel Vetter wrote: > > > > Also mark up follow_pfn as EXPORT_SYMBOL_GPL. The only safe way to use > > > > that by drivers/modules is together with an mmu_notifier, and that's > > > > all _GPL stuff. > > > > > > I also think it also needs to be renamed to explicitly break any existing > > > users out of tree or int the submission queue. > > > > Ok I looked at the mmu notifier locking again and noticed that > > mm->subscriptions has its own spinlock. Since there usually shouldn't > > be a huge pile of these I think it's feasible to check for the mmu > > notifier in follow_pfn. And that would stuff this gap for good. I'll > > throw that on top as a final patch and see what people think. > > Probably the simplest is to just check mm_has_notifiers() when in > lockdep or something very simple like that lockdep feels wrong, was locking more at CONFIG_DEBUG_VM. And since generally you only have 1 mmu notifier (especially for kvm) I think we can also pay the 2nd cacheline miss and actually check the right mmu notifier is registered. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
