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@suse.cz
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