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

[Peter Xu]

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@xxxxxxxxxx>
> > 
> > This allows UFFDIO_COPY to map pages wrprotected.
> > 
> > Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> 
> Minor nitpick down below, but in any case:
> 
> Reviewed-by: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
> 
> > ---
> >  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