On Fri 08-05-15 15:49:22, Mel Gorman wrote:
> On Wed, May 06, 2015 at 09:28:09AM +0200, Jan Kara wrote:
> > Provide new function get_vaddr_frames(). This function maps virtual
> > addresses from given start and fills given array with page frame numbers of
> > the corresponding pages. If given start belongs to a normal vma, the function
> > grabs reference to each of the pages to pin them in memory. If start
> > belongs to VM_IO | VM_PFNMAP vma, we don't touch page structures. Caller
> > must make sure pfns aren't reused for anything else while he is using
> > them.
> >
> > This function is created for various drivers to simplify handling of
> > their buffers.
> >
> > Signed-off-by: Jan Kara <jack@xxxxxxx>
>
> Trivial comments only;
...
> > @@ -936,6 +937,219 @@ int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
> > return ret; /* 0 or negative error code */
> > }
> >
> > +/*
> > + * get_vaddr_frames() - map virtual addresses to pfns
> > + * @start: starting user address
> > + * @nr_frames: number of pages / pfns from start to map
> > + * @write: whether pages will be written to by the caller
> > + * @force: whether to force write access even if user mapping is
> > + * readonly. This will result in the page being COWed even
> > + * in MAP_SHARED mappings. You do not want this.
>
> If they don't want it, why does it exist?
This was copied from get_user_pages(). The original comment changed in
the mean time so I've updated this one somewhat and referenced comment at
get_user_pages() for details.
> > + * @vec: structure which receives pages / pfns of the addresses mapped.
> > + * It should have space for at least nr_frames entries.
> > + *
> > + * This function maps virtual addresses from @start and fills @vec structure
> > + * with page frame numbers or page pointers to corresponding pages (choice
> > + * depends on the type of the vma underlying the virtual address). If @start
> > + * belongs to a normal vma, the function grabs reference to each of the pages
> > + * to pin them in memory. If @start belongs to VM_IO | VM_PFNMAP vma, we don't
> > + * touch page structures and the caller must make sure pfns aren't reused for
> > + * anything else while he is using them.
> > + *
> > + * The function returns number of pages mapped which may be less than
> > + * @nr_frames. In particular we stop mapping if there are more vmas of
> > + * different type underlying the specified range of virtual addresses.
> > + *
> > + * This function takes care of grabbing mmap_sem as necessary.
> > + */
> > +int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
> > + bool write, bool force, struct frame_vector *vec)
> > +{
> > + struct mm_struct *mm = current->mm;
> > + struct vm_area_struct *vma;
> > + int ret = 0;
> > + int err;
> > + int locked = 1;
> > +
>
> bool locked.
It cannot be bool. It is passed to get_user_pages_locked() which expects
int *.
> > + if (nr_frames == 0)
> > + return 0;
> > +
> > + if (WARN_ON_ONCE(nr_frames > vec->nr_allocated))
> > + nr_frames = vec->nr_allocated;
> > +
> > + down_read(&mm->mmap_sem);
> > + vma = find_vma_intersection(mm, start, start + 1);
> > + if (!vma) {
> > + ret = -EFAULT;
> > + goto out;
> > + }
> > + if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
> > + vec->got_ref = 1;
> > + vec->is_pfns = 0;
>
> They're bools and while correct, it looks weird. There are a few
> instances of this but I won't comment on it again.
Thanks. Fixed.
> > + ret = get_user_pages_locked(current, mm, start, nr_frames,
> > + write, force, (struct page **)(vec->ptrs), &locked);
> > + goto out;
> > + }
> > +
> > + vec->got_ref = 0;
> > + vec->is_pfns = 1;
> > + do {
> > + unsigned long *nums = frame_vector_pfns(vec);
> > +
> > + while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) {
> > + err = follow_pfn(vma, start, &nums[ret]);
> > + if (err) {
> > + if (ret == 0)
> > + ret = err;
> > + goto out;
> > + }
> > + start += PAGE_SIZE;
> > + ret++;
> > + }
> > + /*
> > + * We stop if we have enough pages or if VMA doesn't completely
> > + * cover the tail page.
> > + */
> > + if (ret >= nr_frames || start < vma->vm_end)
> > + break;
> > + vma = find_vma_intersection(mm, start, start + 1);
> > + } while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
> > +out:
> > + if (locked)
> > + up_read(&mm->mmap_sem);
> > + if (!ret)
> > + ret = -EFAULT;
> > + if (ret > 0)
> > + vec->nr_frames = ret;
> > + return ret;
> > +}
> > +EXPORT_SYMBOL(get_vaddr_frames);
> > +
> > +/**
> > + * put_vaddr_frames() - drop references to pages if get_vaddr_frames() acquired
> > + * them
> > + * @vec: frame vector to put
> > + *
> > + * Drop references to pages if get_vaddr_frames() acquired them. We also
> > + * invalidate the frame vector so that it is prepared for the next call into
> > + * get_vaddr_frames().
> > + */
> > +void put_vaddr_frames(struct frame_vector *vec)
> > +{
> > + int i;
> > + struct page **pages;
> > +
> > + if (!vec->got_ref)
> > + goto out;
> > + pages = frame_vector_pages(vec);
> > + /*
> > + * frame_vector_pages() might needed to do a conversion when we
> > + * get_vaddr_frames() got pages but vec was later converted to pfns.
> > + * But it shouldn't really fail to convert pfns back...
> > + */
> > + BUG_ON(IS_ERR(pages));
>
> It's hard to see how it could but it is recoverable so BUG_ON is
> overkill. WARN_ON and return even though we potentially leaked now.
OK.
> > + for (i = 0; i < vec->nr_frames; i++)
> > + put_page(pages[i]);
> > + vec->got_ref = 0;
> > +out:
> > + vec->nr_frames = 0;
> > +}
> > +EXPORT_SYMBOL(put_vaddr_frames);
> > +
> > +/**
> > + * frame_vector_to_pages - convert frame vector to contain page pointers
> > + * @vec: frame vector to convert
> > + *
> > + * Convert @vec to contain array of page pointers. If the conversion is
> > + * successful, return 0. Otherwise return an error.
> > + */
>
> If you do another version, it would not hurt to mention that a page
> reference is not taken when doing this conversion.
OK, done.
> > +int frame_vector_to_pages(struct frame_vector *vec)
> > +{
>
> I think it's probably best to make the relevant counters in frame_vector
> signed and limit the maximum possible size of it. It's still not putting
> any practical limit on the size of the frame_vector.
I don't see a reason why counters in frame_vector should be signed... Can
you share your reason? I've added a check into frame_vector_create() to
limit number of frames to INT_MAX / sizeof(void *) / 2 to avoid arithmetics
overflow. Thanks for review!
Honza
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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