[PATCH 2/9] mm: Provide new get_vaddr_frames() helper
Vlastimil Babka
vbabka at suse.cz
Wed May 6 03:45:51 PDT 2015
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 at suse.cz>
Acked-by: Vlastimil Babka <vbabka at 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?
> + * @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?
> + *
> + * 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.
> +
> + 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;
> + 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
remove "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));
> + 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.
> + */
> +int frame_vector_to_pages(struct frame_vector *vec)
> +{
> + int i;
> + unsigned long *nums;
> + struct page **pages;
> +
> + if (!vec->is_pfns)
> + return 0;
> + nums = frame_vector_pfns(vec);
> + for (i = 0; i < vec->nr_frames; i++)
> + if (!pfn_valid(nums[i]))
> + return -EINVAL;
> + pages = (struct page **)nums;
> + for (i = 0; i < vec->nr_frames; i++)
> + pages[i] = pfn_to_page(nums[i]);
> + vec->is_pfns = 0;
> + return 0;
> +}
> +EXPORT_SYMBOL(frame_vector_to_pages);
> +
> +/**
> + * frame_vector_to_pfns - convert frame vector to contain pfns
> + * @vec: frame vector to convert
> + *
> + * Convert @vec to contain array of pfns.
> + */
> +void frame_vector_to_pfns(struct frame_vector *vec)
> +{
> + int i;
> + unsigned long *nums;
> + struct page **pages;
> +
> + if (vec->is_pfns)
> + return;
> + pages = (struct page **)(vec->ptrs);
> + nums = (unsigned long *)pages;
> + for (i = 0; i < vec->nr_frames; i++)
> + nums[i] = page_to_pfn(pages[i]);
> + vec->is_pfns = 1;
> +}
> +EXPORT_SYMBOL(frame_vector_to_pfns);
> +
> +/**
> + * frame_vector_create() - allocate & initialize structure for pinned pfns
> + * @nr_frames: number of pfns slots we should reserve
> + *
> + * Allocate and initialize struct pinned_pfns to be able to hold @nr_pfns
> + * pfns.
> + */
> +struct frame_vector *frame_vector_create(unsigned int nr_frames)
> +{
> + struct frame_vector *vec;
> + int size = sizeof(struct frame_vector) + sizeof(void *) * nr_frames;
> +
> + if (WARN_ON_ONCE(nr_frames == 0))
> + return NULL;
> + /*
> + * Avoid higher order allocations, use vmalloc instead. It should
> + * be rare anyway.
> + */
> + if (size <= PAGE_SIZE)
> + vec = kmalloc(size, GFP_KERNEL);
> + else
> + vec = vmalloc(size);
> + if (!vec)
> + return NULL;
> + vec->nr_allocated = nr_frames;
> + vec->nr_frames = 0;
> + return vec;
> +}
> +EXPORT_SYMBOL(frame_vector_create);
> +
> +/**
> + * 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?
> + if (!is_vmalloc_addr(vec))
> + kfree(vec);
> + else
> + vfree(vec);
> +}
> +EXPORT_SYMBOL(frame_vector_destroy);
> +
> /**
> * get_dump_page() - pin user page in memory while writing it to core dump
> * @addr: user address
>
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