Re: [PATCH 1/9] mm: Provide new get_vaddr_pfns() helper

[Jan Kara <jack@suse.cz>]

On Mon 17-03-14 20:49:28, Jan Kara wrote:
> Provide new function get_vaddr_pfns().  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
> should 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.
  MM guys, could you have a look at this patch? Linux Media people like the
abstraction of buffer handling and would like to merge the patch set (see
http://thread.gmane.org/gmane.linux.drivers.video-input-infrastructure/89268).
But for that they need ack from mm people that the interface is ok with
them. So far the only comment I got regarding the interface was from Dave
Hansen that I could also handle VM_MIXEDMAP mappings - I could if people
really want that but so far there are no users for that. Thanks!

								Honza
> 
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  include/linux/mm.h |  46 +++++++++++++++
>  mm/memory.c        | 165 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 211 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index da8ad480bea7..b3bd29cc40dd 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -18,6 +18,8 @@
>  #include <linux/pfn.h>
>  #include <linux/bit_spinlock.h>
>  #include <linux/shrinker.h>
> +#include <linux/slab.h>
> +#include <linux/vmalloc.h>
>  
>  struct mempolicy;
>  struct anon_vma;
> @@ -1180,6 +1182,50 @@ get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
>  	return ret;
>  }
>  
> +/* Container for pinned pfns / pages */
> +struct pinned_pfns {
> +	unsigned int nr_allocated_pfns;	/* Number of pfns we have space for */
> +	unsigned int nr_pfns;		/* Number of pfns stored in pfns array */
> +	unsigned int got_ref:1;		/* Did we pin pfns by getting page ref? */
> +	unsigned int is_pages:1;	/* 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 pinned_pfns *pfns_vector_create(int nr_pfns);
> +static inline void pfns_vector_destroy(struct pinned_pfns *pfns)
> +{
> +	if (!is_vmalloc_addr(pfns))
> +		kfree(pfns);
> +	else
> +		vfree(pfns);
> +}
> +int get_vaddr_pfns(unsigned long start, int nr_pfns, int write, int force,
> +		   struct pinned_pfns *pfns);
> +void put_vaddr_pfns(struct pinned_pfns *pfns);
> +int pfns_vector_to_pages(struct pinned_pfns *pfns);
> +
> +static inline int pfns_vector_count(struct pinned_pfns *pfns)
> +{
> +	return pfns->nr_pfns;
> +}
> +
> +static inline struct page **pfns_vector_pages(struct pinned_pfns *pfns)
> +{
> +	if (!pfns->is_pages)
> +		return NULL;
> +	return (struct page **)(pfns->ptrs);
> +}
> +
> +static inline unsigned long *pfns_vector_pfns(struct pinned_pfns *pfns)
> +{
> +	if (pfns->is_pages)
> +		return NULL;
> +	return (unsigned long *)(pfns->ptrs);
> +}
> +
> +
>  struct kvec;
>  int get_kernel_pages(const struct kvec *iov, int nr_pages, int write,
>  			struct page **pages);
> diff --git a/mm/memory.c b/mm/memory.c
> index 22dfa617bddb..87bebcfb8911 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2024,6 +2024,171 @@ long get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
>  EXPORT_SYMBOL(get_user_pages);
>  
>  /**
> + * get_vaddr_pfns() - map virtual addresses to pfns
> + * @start:	starting user address
> + * @nr_pfns:	number of 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.
> + * @pfns:	structure which receives pfns of the pages mapped.
> + *		It should have space for at least nr_pfns pfns. 
> + *
> + * This function maps virtual addresses from @start and fills @pfns structure
> + * with page frame numbers of corresponding pages. 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. Caller should make sure pfns aren't reused for anything else
> + * while he is using them.
> + *
> + * This function takes care of grabbing mmap_sem as necessary.
> + */
> +int get_vaddr_pfns(unsigned long start, int nr_pfns, int write, int force,
> +		   struct pinned_pfns *pfns)
> +{
> +	struct mm_struct *mm = current->mm;
> +	struct vm_area_struct *vma;
> +	int ret = 0;
> +	int err;
> +
> +	if (nr_pfns <= 0)
> +		return 0;
> +
> +	if (nr_pfns > pfns->nr_allocated_pfns)
> +		nr_pfns = pfns->nr_allocated_pfns;
> +
> +	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))) {
> +		pfns->got_ref = 1;
> +		pfns->is_pages = 1;
> +		ret = get_user_pages(current, mm, start, nr_pfns, write, force,
> +				     pfns_vector_pages(pfns), NULL);
> +		goto out;
> +	}
> +
> +	pfns->got_ref = 0;
> +	pfns->is_pages = 0;
> +	do {
> +		unsigned long *nums = pfns_vector_pfns(pfns);
> +
> +		while (ret < nr_pfns && 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_pfns || start < vma->vm_end)
> +			break;
> +		vma = find_vma_intersection(mm, start, start + 1);
> +	} while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
> +out:
> +	up_read(&mm->mmap_sem);
> +	if (!ret)
> +		ret = -EFAULT;
> +	if (ret > 0)
> +		pfns->nr_pfns = ret;
> +	return ret;
> +}
> +EXPORT_SYMBOL(get_vaddr_pfns);
> +
> +/**
> + * put_vaddr_pfns() - drop references to pages if get_vaddr_pfns() acquired them
> + * @pfns:     structure with pfns we pinned
> + *
> + * Drop references to pages if get_vaddr_pfns() acquired them. We also
> + * invalidate the array of pfns so that it is prepared for the next call into
> + * get_vaddr_pfns().
> + */
> +void put_vaddr_pfns(struct pinned_pfns *pfns)
> +{
> +	int i;
> +
> +	if (!pfns->got_ref)
> +		goto out;
> +	if (pfns->is_pages) {
> +		struct page **pages = pfns_vector_pages(pfns);
> +
> +		for (i = 0; i < pfns->nr_pfns; i++)
> +			put_page(pages[i]);
> +	} else {
> +		unsigned long *nums = pfns_vector_pfns(pfns);
> +
> +		for (i = 0; i < pfns->nr_pfns; i++)
> +			put_page(pfn_to_page(nums[i]));
> +	}
> +	pfns->got_ref = 0;
> +out:
> +	pfns->nr_pfns = 0;
> +}
> +EXPORT_SYMBOL(put_vaddr_pfns);
> +
> +/**
> + * pfns_vector_to_pages - convert vector of pfns to vector of page pointers
> + * @pfns:	structure with pinned pfns
> + *
> + * Convert @pfns to not contain array of pfns but array of page pointers.
> + * If the conversion is successful, return 0. Otherwise return an error.
> + */
> +int pfns_vector_to_pages(struct pinned_pfns *pfns)
> +{
> +	int i;
> +	unsigned long *nums;
> +	struct page **pages;
> +
> +	if (pfns->is_pages)
> +		return 0;
> +	nums = pfns_vector_pfns(pfns);
> +	for (i = 0; i < pfns->nr_pfns; i++)
> +		if (!pfn_valid(nums[i]))
> +			return -EINVAL;
> +	pages = (struct page **)nums;
> +	for (i = 0; i < pfns->nr_pfns; i++)
> +		pages[i] = pfn_to_page(nums[i]);
> +	pfns->is_pages = 1;
> +	return 0;
> +}
> +EXPORT_SYMBOL(pfns_vector_to_pages);
> +
> +/**
> + * pfns_vector_create() - allocate & initialize structure for pinned pfns
> + * @nr_pfns:	number of pfns slots we should reserve
> + *
> + * Allocate and initialize struct pinned_pfns to be able to hold @nr_pfns
> + * pfns.
> + */
> +struct pinned_pfns *pfns_vector_create(int nr_pfns)
> +{
> +	struct pinned_pfns *pfns;
> +	int size = sizeof(struct pinned_pfns) + sizeof(unsigned long) * nr_pfns;
> +
> +	if (WARN_ON_ONCE(nr_pfns <= 0))
> +		return NULL;
> +	if (size <= PAGE_SIZE)
> +		pfns = kmalloc(size, GFP_KERNEL);
> +	else
> +		pfns = vmalloc(size);
> +	if (!pfns)
> +		return NULL;
> +	pfns->nr_allocated_pfns = nr_pfns;
> +	pfns->nr_pfns = 0;
> +	return 0;
> +}
> +EXPORT_SYMBOL(pfns_vector_create);
> +
> +/**
>   * get_dump_page() - pin user page in memory while writing it to core dump
>   * @addr: user address
>   *
> -- 
> 1.8.1.4
> 
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

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