> On Mar 2, 2021, at 2:13 PM, Peter Xu wrote: > > On Fri, Dec 25, 2020 at 01:25:27AM -0800, Nadav Amit wrote: >> From: Nadav Amit >> >> This patch-set went from v1 to RFCv2, as there is still an ongoing >> discussion regarding the way of solving the recently found races due to >> deferred TLB flushes. These patches are only sent for reference for now, >> and can be applied later if no better solution is taken. >> >> In a nutshell, write-protecting PTEs with deferred TLB flushes was mostly >> performed while holding mmap_lock for write. This prevented concurrent >> page-fault handler invocations from mistakenly assuming that a page is >> write-protected when in fact, due to the deferred TLB flush, other CPU >> could still write to the page. Such a write can cause a memory >> corruption if it takes place after the page was copied (in >> cow_user_page()), and before the PTE was flushed (by wp_page_copy()). >> >> However, the userfaultfd and soft-dirty mechanisms did not take >> mmap_lock for write, but only for read, which made such races possible. >> Since commit 09854ba94c6a ("mm: do_wp_page() simplification") these >> races became more likely to take place as non-COW'd pages are more >> likely to be COW'd instead of being reused. Both of the races that >> these patches are intended to resolve were produced on v5.10. >> >> To avoid the performance overhead some alternative solutions that do not >> require to acquire mmap_lock for write were proposed, specifically for >> userfaultfd. So far no better solution that can be backported was >> proposed for the soft-dirty case. >> >> v1->RFCv2: >> - Better (i.e., correct) description of the userfaultfd buggy case [Yu] >> - Patch for the soft-dirty case > > Nadav, > > Do you plan to post a new version to fix the tlb corrupt issue that this series > wanted to solve? Yes, yes. Sorry for that. Will do so later today. Regards, Nadav