> On Mar 3, 2021, at 11:03 AM, Peter Xu wrote: > > On Wed, Mar 03, 2021 at 01:57:02AM -0800, Nadav Amit wrote: >> From: Nadav Amit >> >> Userfaultfd self-test fails occasionally, indicating a memory >> corruption. > > It's failing very constantly now for me after I got it run on a 40 cores > system... While indeed not easy to fail on my laptop. > It fails rather constantly for me, but since nobody else reproduced it, I was afraid to say otherwise ;-) > >> Fixes: 292924b26024 ("userfaultfd: wp: apply _PAGE_UFFD_WP bit") >> Signed-off-by: Nadav Amit >> >> --- >> v2->v3: >> * Do not acquire mmap_lock for write, flush conditionally instead [Yu] >> * Change the fixes tag to the patch that made the race apparent [Yu] > > Did you forget about this one? It would still be good to point to 09854ba94c6a > just to show that 5.7/5.8 stable branches shouldn't need this patch as they're > not prone to the tlb data curruption. Maybe also cc stable with 5.9+? The fixes tag is wrong, as you say. I will fix it and cc stable with 5.9+. > >> * Removing patch to avoid write-protect on uffd unprotect. More >> comprehensive solution to follow (and avoid the TLB flush as well). >> --- >> mm/memory.c | 7 +++++++ >> 1 file changed, 7 insertions(+) >> >> diff --git a/mm/memory.c b/mm/memory.c >> index 9e8576a83147..06da04f98936 100644 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -3092,6 +3092,13 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) >> return handle_userfault(vmf, VM_UFFD_WP); >> } >> >> + /* >> + * Userfaultfd write-protect can defer flushes. Ensure the TLB >> + * is flushed in this case before copying. >> + */ >> + if (userfaultfd_wp(vmf->vma) && mm_tlb_flush_pending(vmf->vma->vm_mm)) >> + flush_tlb_page(vmf->vma, vmf->address); >> + >> vmf->page = vm_normal_page(vma, vmf->address, vmf->orig_pte); >> if (!vmf->page) { >> /* >> -- >> 2.25.1 >> > > Thanks for being consistent on fixing this problem. > > Maybe it's even better to put that into a "unlikely" to reduce the affect of > normal do_wp_page as much as possible? But I'll leave it to others. > > If with the fixes tag modified: > > Reviewed-by: Peter Xu > Tested-by: Peter Xu Thanks, I will send v4 later today. Regards, Nadav