On Wed, Dec 04, 2024 at 04:31:00PM +0100, David Hildenbrand wrote: > If we have to trigger a hugetlb folio copy during fork() because the anon > folio might be pinned, we currently unconditionally create a writable > PTE. > > However, the VMA might not have write permissions (VM_WRITE) at that > point. > > Fix it by checking the VMA for VM_WRITE. Make the code less error prone > by moving checking for VM_WRITE into make_huge_pte(), and letting > callers only specify whether we should try making it writable. > > A simple reproducer that longter-pins the folios using liburing to then > mprotect(PROT_READ) the folios befor fork() [1] results in: > > Before: > [FAIL] access should not have worked > > After: > [PASS] access did not work as expected > > [1] https://gitlab.com/davidhildenbrand/scratchspace/-/raw/main/reproducers/hugetlb-mkwrite-fork.c > > This is rather a corner case, so stable might not be warranted. > > Fixes: 4eae4efa2c29 ("hugetlb: do early cow when page pinned on src mm") > Cc: Muchun Song <muchun.song@xxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Peter Xu <peterx@xxxxxxxxxx> > Cc: Guillaume Morin <guillaume@xxxxxxxxxxx> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Acked-by: Peter Xu <peterx@xxxxxxxxxx> Thanks, -- Peter Xu
