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frame_vector.c 6.07 KiB
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    #include <linux/kernel.h>
    #include <linux/errno.h>
    #include <linux/err.h>
    #include <linux/mm.h>
    #include <linux/slab.h>
    #include <linux/vmalloc.h>
    #include <linux/pagemap.h>
    #include <linux/sched.h>
    
    /**
     * get_vaddr_frames() - map virtual addresses to pfns
     * @start:	starting user address
     * @nr_frames:	number of pages / pfns from start to map
     * @gup_flags:	flags modifying lookup behaviour
     * @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.
     * When the function isn't able to map a single page, it returns error.
     *
     * This function takes care of grabbing mmap_sem as necessary.
     */
    int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
    		     unsigned int gup_flags, struct frame_vector *vec)
    {
    	struct mm_struct *mm = current->mm;
    	struct vm_area_struct *vma;
    	int ret = 0;
    	int err;
    	int locked;
    
    	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);
    	locked = 1;
    	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 = true;
    		vec->is_pfns = false;
    		ret = get_user_pages_locked(start, nr_frames,
    			gup_flags, (struct page **)(vec->ptrs), &locked);
    		goto out;
    	}
    
    	vec->got_ref = false;
    	vec->is_pfns = true;
    	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
    	 * get_vaddr_frames() got pages but vec was later converted to pfns.
    	 * But it shouldn't really fail to convert pfns back...
    	 */
    	if (WARN_ON(IS_ERR(pages)))
    		goto out;
    	for (i = 0; i < vec->nr_frames; i++)
    		put_page(pages[i]);
    	vec->got_ref = false;
    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. Note that we do not grab
     * page references for the page structures.
     */
    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 = false;
    	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 = true;
    }
    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;
    	/*
    	 * This is absurdly high. It's here just to avoid strange effects when
    	 * arithmetics overflows.
    	 */
    	if (WARN_ON_ONCE(nr_frames > INT_MAX / sizeof(void *) / 2))
    		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)
    {
    	/* Make sure put_vaddr_frames() got called properly... */
    	VM_BUG_ON(vec->nr_frames > 0);
    	kvfree(vec);
    }
    EXPORT_SYMBOL(frame_vector_destroy);