Re: [PATCH v2 10/26] userfaultfd: wp: add UFFDIO_COPY_MODE_WP

Peter Xu
2019-02-22T07:11:23Z

On Thu, Feb 21, 2019 at 12:29:19PM -0500, Jerome Glisse wrote:
> On Tue, Feb 12, 2019 at 10:56:16AM +0800, Peter Xu wrote:
> > From: Andrea Arcangeli <aarcange@redhat.com>
> >
> > This allows UFFDIO_COPY to map pages wrprotected.
> >
> > Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
> > Signed-off-by: Peter Xu <peterx@redhat.com>
>
> Minor nitpick down below, but in any case:
>
> Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
>
> > ---
> > fs/userfaultfd.c | 5 +++--
> > include/linux/userfaultfd_k.h | 2 +-
> > include/uapi/linux/userfaultfd.h | 11 +++++-----
> > mm/userfaultfd.c | 36 ++++++++++++++++++++++----------
> > 4 files changed, 35 insertions(+), 19 deletions(-)
> >
>
> [...]
>
> > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> > index d59b5a73dfb3..73a208c5c1e7 100644
> > --- a/mm/userfaultfd.c
> > +++ b/mm/userfaultfd.c
> > @@ -25,7 +25,8 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
> > struct vm_area_struct *dst_vma,
> > unsigned long dst_addr,
> > unsigned long src_addr,
> > - struct page **pagep)
> > + struct page **pagep,
> > + bool wp_copy)
> > {
> > struct mem_cgroup *memcg;
> > pte_t _dst_pte, *dst_pte;
> > @@ -71,9 +72,9 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
> > if (mem_cgroup_try_charge(page, dst_mm, GFP_KERNEL, &memcg, false))
> > goto out_release;
> >
> > - _dst_pte = mk_pte(page, dst_vma->vm_page_prot);
> > - if (dst_vma->vm_flags & VM_WRITE)
> > - _dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));
> > + _dst_pte = pte_mkdirty(mk_pte(page, dst_vma->vm_page_prot));
> > + if (dst_vma->vm_flags & VM_WRITE && !wp_copy)
> > + _dst_pte = pte_mkwrite(_dst_pte);
>
> I like parenthesis around around and :) ie:
> (dst_vma->vm_flags & VM_WRITE) && !wp_copy
>
> I feel it is easier to read.

Yeah another one. Though this line will be changed in follow up
patches, will fix anyways.

>
> [...]
>
> > @@ -416,11 +418,13 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
> > if (!(dst_vma->vm_flags & VM_SHARED)) {
> > if (!zeropage)
> > err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
> > - dst_addr, src_addr, page);
> > + dst_addr, src_addr, page,
> > + wp_copy);
> > else
> > err = mfill_zeropage_pte(dst_mm, dst_pmd,
> > dst_vma, dst_addr);
> > } else {
> > + VM_WARN_ON(wp_copy); /* WP only available for anon */
>
> Don't you want to return with error here ?

Makes sense to me. Does this looks good to you to be squashed into
current patch?

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 73a208c5c1e7..f3ea09f412d4 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -73,7 +73,7 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
goto out_release;

_dst_pte = pte_mkdirty(mk_pte(page, dst_vma->vm_page_prot));
- if (dst_vma->vm_flags & VM_WRITE && !wp_copy)
+ if ((dst_vma->vm_flags & VM_WRITE) && !wp_copy)
_dst_pte = pte_mkwrite(_dst_pte);

dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
@@ -424,7 +424,10 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
err = mfill_zeropage_pte(dst_mm, dst_pmd,
dst_vma, dst_addr);
} else {
- VM_WARN_ON(wp_copy); /* WP only available for anon */
+ if (unlikely(wp_copy))
+ /* TODO: WP currently only available for anon */
+ return -EINVAL;
+
if (!zeropage)
err = shmem_mcopy_atomic_pte(dst_mm, dst_pmd,
dst_vma, dst_addr,

Thanks,

--
Peter Xu