On Fri, Oct 04, 2019 at 07:28:34PM -0400, Andrea Arcangeli wrote: >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. > ok, I get your point. >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> Reviewed-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx> >--- > 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), -- Wei Yang Help you, Help me
