Hello, On Tue, Aug 06, 2019 at 01:38:59PM +0800, Wei Yang wrote: > Finally new_flags equals old vm_flags *OR* vm_flags. > > It is not necessary to mask them first. > > Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx> > --- > fs/userfaultfd.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > index ccbdbd62f0d8..653d8f7c453c 100644 > --- a/fs/userfaultfd.c > +++ b/fs/userfaultfd.c > @@ -1457,7 +1457,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx, > start = vma->vm_start; > vma_end = min(end, vma->vm_end); > > - new_flags = (vma->vm_flags & ~vm_flags) | vm_flags; > + new_flags = vma->vm_flags | vm_flags; > prev = vma_merge(mm, prev, start, vma_end, new_flags, > vma->anon_vma, vma->vm_file, vma->vm_pgoff, > vma_policy(vma), And then how do you clear the flags after the above? It must be possible to clear the flags (from UFFDIO_REGISTER_MODE_MISSING|UFFDIO_REGISTER_MODE_WP to only one set or invert). We have no WP support upstream yet, so maybe that's why it looks superfluous in practice, but in theory it isn't because it would then need to be reversed by Peter's (CC'ed) -wp patchset. The register code has already the right placeholder to support -wp and so it's better not to break them. I would recommend reviewing the uffd-wp support and working on testing the uffd-wp code instead of changing the above. Thanks, Andrea
