Hi, On Sat, Jan 12, 2019 at 12:36:29AM +0000, Blake Caldwell wrote: > Moving a page out of a userfaultfd registered region and into a userland > anonymous vma is needed by the use case of uncooperatively limiting the > resident size of the userfaultfd region. Reverse the direction of the > original userfaultfd_remap() to the out direction. Now after memory has > been removed, subsequent accesses will generate uffdio page fault events. It took me a while but better late then never :) Why did you keep this as a separate patch? If the primary use case for UFFDIO_REMAP to move pages out of userfaultfd region, why not make it so from the beginning? > Signed-off-by: Blake Caldwell <blake.caldwell@xxxxxxxxxxxx> > --- > Documentation/admin-guide/mm/userfaultfd.rst | 10 ++++++++++ > fs/userfaultfd.c | 6 +++--- > 2 files changed, 13 insertions(+), 3 deletions(-) > > diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst > index 5048cf6..714af49 100644 > --- a/Documentation/admin-guide/mm/userfaultfd.rst > +++ b/Documentation/admin-guide/mm/userfaultfd.rst > @@ -108,6 +108,16 @@ UFFDIO_COPY. They're atomic as in guaranteeing that nothing can see an > half copied page since it'll keep userfaulting until the copy has > finished. > > +To move pages out of a userfault registered region and into a user vma > +the UFFDIO_REMAP ioctl can be used. This is only possible for the > +"OUT" direction. For the "IN" direction, UFFDIO_COPY is preferred > +since UFFDIO_REMAP requires a TLB flush on the source range at a > +greater penalty than copying the page. With > +UFFDIO_REGISTER_MODE_MISSING set, subsequent accesses to the same > +region will generate a page fault event. This allows non-cooperative > +removal of memory in a userfaultfd registered vma, effectively > +limiting the amount of resident memory in such a region. > + > QEMU/KVM > ======== > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > index cf68cdb..8099da2 100644 > --- a/fs/userfaultfd.c > +++ b/fs/userfaultfd.c > @@ -1808,10 +1808,10 @@ static int userfaultfd_remap(struct userfaultfd_ctx *ctx, > sizeof(uffdio_remap)-sizeof(__s64))) > goto out; > > - ret = validate_range(ctx->mm, uffdio_remap.dst, uffdio_remap.len); > + ret = validate_range(current->mm, uffdio_remap.dst, uffdio_remap.len); > if (ret) > goto out; > - ret = validate_range(current->mm, uffdio_remap.src, uffdio_remap.len); > + ret = validate_range(ctx->mm, uffdio_remap.src, uffdio_remap.len); > if (ret) > goto out; > ret = -EINVAL; > @@ -1819,7 +1819,7 @@ static int userfaultfd_remap(struct userfaultfd_ctx *ctx, > UFFDIO_REMAP_MODE_DONTWAKE)) > goto out; > > - ret = remap_pages(ctx->mm, current->mm, > + ret = remap_pages(current->mm, ctx->mm, > uffdio_remap.dst, uffdio_remap.src, > uffdio_remap.len, uffdio_remap.mode); > if (unlikely(put_user(ret, &user_uffdio_remap->remap))) > -- > 1.8.3.1 > -- Sincerely yours, Mike.
