On Thu, Apr 1, 2021 at 11:17 AM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > We received a report that the copy-on-write issue repored by Jann Horn in > https://bugs.chromium.org/p/project-zero/issues/detail?id=2045 is still > reproducible on 4.14 and 4.19 kernels (the first issue with the reproducer > coded in vmsplice.c). Gaah. > I confirmed this and also that the issue was not > reproducible with 5.10 kernel. I tracked the fix to the following patch > introduced in 5.9 which changes the do_wp_page() logic: > > 09854ba94c6a 'mm: do_wp_page() simplification' The problem here is that there's a _lot_ more patches than the few you found that fixed various other cases (THP etc). > I backported this patch (#2 in the series) along with 2 prerequisite patches > (#1 and #4) that keep the backports clean and two followup fixes to the main > patch (#3 and #5). I had to skip the following fix: > > feb889fb40fa 'mm: don't put pinned pages into the swap cache' > > because it uses page_maybe_dma_pinned() which does not exists in earlier > kernels. Because pin_user_pages() does not exist there as well, I *think* > we can safely skip this fix on older kernels, but I would appreciate if > someone could confirm that claim. Hmm. I think this means that swap activity can now break the connection to a GUP page (the whole pre-pinning model), but it probably isn't a new problem for 4.9/4.19. I suspect the test there should be something like /* Single mapper, more references than us and the map? */ if (page_mapcount(page) == 1 && page_count(page) > 2) goto keep_locked; in the pre-pinning days. But I really think that there are a number of other commits you're missing too, because we had a whole series for THP fixes for the same exact issue. Added Peter Xu to the cc, because he probably tracked those issues better than I did. So NAK on this for now, I think this limited patch-set likely introduces more problems than it fixes. Linus
