On Wed 06-05-15 12:45:51, Vlastimil Babka wrote:
On 05/06/2015 09:28 AM, 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
Acked-by: Vlastimil Babka vbabka@suse.cz
With some nitpicks below...
include/linux/mm.h | 44 +++++++++++ mm/gup.c | 214 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 258 insertions(+)
diff --git a/include/linux/mm.h b/include/linux/mm.h index 0755b9fd03a7..dcd1f02a78e9 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -20,6 +20,7 @@ #include <linux/shrinker.h> #include <linux/resource.h> #include <linux/page_ext.h> +#include <linux/err.h>
struct mempolicy; struct anon_vma; @@ -1197,6 +1198,49 @@ long get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm, int write, int force, struct page **pages); int get_user_pages_fast(unsigned long start, int nr_pages, int write, struct page **pages);
+/* Container for pinned pfns / pages */ +struct frame_vector {
- unsigned int nr_allocated; /* Number of frames we have space for */
- unsigned int nr_frames; /* Number of frames stored in ptrs array */
- bool got_ref; /* Did we pin pages by getting page ref? */
- bool is_pfns; /* Does array contain pages or pfns? */
- void *ptrs[0]; /* Array of pinned pfns / pages. Use
* pfns_vector_pages() or pfns_vector_pfns()* for access */+};
+struct frame_vector *frame_vector_create(unsigned int nr_frames); +void frame_vector_destroy(struct frame_vector *vec); +int get_vaddr_frames(unsigned long start, unsigned int nr_pfns,
bool write, bool force, struct frame_vector *vec);+void put_vaddr_frames(struct frame_vector *vec); +int frame_vector_to_pages(struct frame_vector *vec); +void frame_vector_to_pfns(struct frame_vector *vec);
+static inline unsigned int frame_vector_count(struct frame_vector *vec) +{
- return vec->nr_frames;
+}
+static inline struct page **frame_vector_pages(struct frame_vector *vec) +{
- if (vec->is_pfns) {
int err = frame_vector_to_pages(vec);if (err)return ERR_PTR(err);- }
- return (struct page **)(vec->ptrs);
+}
+static inline unsigned long *frame_vector_pfns(struct frame_vector *vec) +{
- if (!vec->is_pfns)
frame_vector_to_pfns(vec);- return (unsigned long *)(vec->ptrs);
+}
struct kvec; int get_kernel_pages(const struct kvec *iov, int nr_pages, int write, struct page **pages); diff --git a/mm/gup.c b/mm/gup.c index 6297f6bccfb1..8db5c40e65c4 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -8,6 +8,7 @@ #include <linux/rmap.h> #include <linux/swap.h> #include <linux/swapops.h> +#include <linux/vmalloc.h>
#include <linux/sched.h> #include <linux/rwsem.h> @@ -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."You do not want this" and yet some of the drivers in later patches do. That looks weird. Explain better?
That was copied from get_user_pages() comment but that got changed in the mean time. I've referenced that instead of copying it.
- @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.
The function can also return e.g. -EFAULT, shouldn't that be documented too?
I've added a comment that the function can return error.
- 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;
It looks strange that locked is set to 1 before taking the actual mmap_sem. Also future-proofing.
OK.
+/**
- frame_vector_destroy() - free memory allocated to carry frame vector
- @vec: Frame vector to free
- Free structure allocated by frame_vector_create() to carry frames.
- */
+void frame_vector_destroy(struct frame_vector *vec) +{
Add some VM_BUG_ON()'s for nr_frames and got_ref perhaps?
Good idea. Added: VM_BUG_ON(vec->nr_frames > 0); Asserting got_ref when nr_frames is 0 is pointless... Thanks for review!
Honza