On Tue, Aug 29, 2017 at 12:58:45PM -0700, Linus Torvalds wrote: > On Tue, Aug 29, 2017 at 12:16 PM, Linus Torvalds > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > And then you can check if something actually happened by catching the > > *ATOMIC* call to mmu_notifier_invalidate_page(), setting a flag, and > > then doing something blocking at mmu_notifier_invalidate_range_end() > > time. > > > > Maybe. > > Note that now I have looked more at the users, I think we actually > just want to get rid of mmu_notifier_invalidate_page() entirely in > favor of just calling mmu_notifier_invalidate_range_start()/end(). > > Nobody seems to want an atomic version of > mmu_notifier_invalidate_page(), they are perfectly happy just getting > those range_start/end() call instead. > > HOWEVER. > > There do seem to be places (eg powernv/npu-dma.c, iommu/amd_iommu_v2.c > and ommu/intel-svm.c) that want to get the "invalidate_page()" or > "invalidate_range()" calls, but do *not* catch the begin/end() ones. > The "range" calls were for atomic cases, and the "page" call was for > the few places that weren't (but should have been). They seem to do > the same things. > > So just switching from mmu_notifier_invalidate_page() to the > "invalidate_range_start()/end()" pair instead could break those cases. > > But the mmu_notifier_invalidate_range() call has always been atomic, > afaik. It's called from the ptep_clear_flush_notify(), which is > called while holdin gthe ptl lock as far as I can tell. > > So to handle the powernv/npu-dma.c, iommu/amd_iommu_v2.c and > ommu/intel-svm.c correctly, _and_ get he KVM case right, we probably > need to: > > - replace the existing mmu_notifier_invalidate_page() call with > mmu_notifier_invalidate_range(), and make sure it's inside the locked > region (ie fs/dax.c too - actually move it inside the lock) > > - surround the locked region with those > mmu_notifier_invalidate_range_start()/end() calls. > > - get rid of mmu_notifier_invalidate_page() entirely, it had bad > semantics anyway. > > and from all I can tell that should work for everybody. > > But maybe I'm missing something. > So ignore what i just sent, i will rework it toward that direction. I believe you are right. Jérôme -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
