On Sat, Oct 05, 2019 at 06:46:40AM +0800, Wei Yang wrote: > On Wed, Oct 02, 2019 at 08:45:05PM -0400, Andrea Arcangeli wrote: > >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. > > > > Sorry, I don't get your point. This change is valid to me even from arithmetic > point of view. > > vm_flags == VM_UFFD_MISSING | VM_UFFD_WP > > The effect of current code is clear these two bits then add them. This equals > to just add these two bits. > > I am not sure which part I lost. The cleaned removed the "& ~" and that was enough to quickly tell the cleaned up version was wrong. What I should have noticed right away as well is that the code was already wrong, sorry. That code doesn't require a noop code cleanup, it requires a fix and the "& ~" needs to stay. This isn't going to make any difference upstream until the uffd-wp support is merged so it is enough to queue it in Peter's queue, or you can merge it independently. Thanks, Andrea >From a0f17bef184c6bb9b99294f202eefb50b6eb43cd Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli <aarcange@xxxxxxxxxx> Date: Fri, 4 Oct 2019 19:09:59 -0400 Subject: [PATCH 1/1] uffd: wp: clear VM_UFFD_MISSING or VM_UFFD_WP during userfaultfd_register() If the registration is repeated without VM_UFFD_MISSING or VM_UFFD_WP they need to be cleared. Currently setting UFFDIO_REGISTER_MODE_WP returns -EINVAL, so this patch is a noop until the UFFDIO_REGISTER_MODE_WP support is applied. Reported-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx> Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> --- fs/userfaultfd.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index fe6d804a38dc..97596bb65dd5 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -1458,7 +1458,8 @@ 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_UFFD_MISSING|VM_UFFD_WP)) | vm_flags; prev = vma_merge(mm, prev, start, vma_end, new_flags, vma->anon_vma, vma->vm_file, vma->vm_pgoff, vma_policy(vma),
