Re: [PATCH] videobuf2-dma-sg: Support io userptr operations on io memory

Marek Szyprowski
2013-11-26T11:20:44Z

Hello,

On 2013-11-06 20:48, Ricardo Ribalda Delgado wrote:
> Memory exported via remap_pfn_range cannot be remapped via
> get_user_pages.
>
> Other videobuf2 methods (like the dma-contig) supports io memory.
>
> This patch adds support for this kind of memory.
>
> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
> ---
> drivers/media/v4l2-core/videobuf2-dma-sg.c | 35 ++++++++++++++++++++++++++----
> 1 file changed, 31 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/videobuf2-dma-sg.c b/drivers/media/v4l2-core/videobuf2-dma-sg.c
> index 2f86054..44ddfe1 100644
> --- a/drivers/media/v4l2-core/videobuf2-dma-sg.c
> +++ b/drivers/media/v4l2-core/videobuf2-dma-sg.c
> @@ -40,6 +40,7 @@ struct vb2_dma_sg_buf {
> unsigned int num_pages;
> atomic_t refcount;
> struct vb2_vmarea_handler handler;
> + struct vm_area_struct *vma;
> };
>
> static void vb2_dma_sg_put(void *buf_priv);
> @@ -155,6 +156,11 @@ static void vb2_dma_sg_put(void *buf_priv)
> }
> }
>
> +static inline int vma_is_io(struct vm_area_struct *vma)
> +{
> + return !!(vma->vm_flags & (VM_IO | VM_PFNMAP));
> +}
> +
> static void *vb2_dma_sg_get_userptr(void *alloc_ctx, unsigned long vaddr,
> unsigned long size, int write)
> {
> @@ -180,7 +186,26 @@ static void *vb2_dma_sg_get_userptr(void *alloc_ctx, unsigned long vaddr,
> if (!buf->pages)
> return NULL;
>
> - num_pages_from_user = get_user_pages(current, current->mm,
> + buf->vma = find_vma(current->mm, vaddr);
> + if (!buf->vma) {
> + dprintk(1, "no vma for address %lu\n", vaddr);
> + return NULL;
> + }
> +
> + if (vma_is_io(buf->vma)) {
> + for (num_pages_from_user = 0;
> + num_pages_from_user < buf->num_pages;
> + ++num_pages_from_user, vaddr += PAGE_SIZE) {
> + unsigned long pfn;
> +
> + if (follow_pfn(buf->vma, vaddr, &pfn)) {
> + dprintk(1, "no page for address %lu\n", vaddr);
> + break;
> + }

Please add a call to vb2_get_vma(vma) to protect that io memory from
being freed, see videobuf2-dma-contig.c for the reference. It is not
100% perfect way, but right now it works for the typical memory regions
created by other multimedia devices. You will also need to call
vb2_put_vma() later on release.

> + buf->pages[num_pages_from_user] = pfn_to_page(pfn);
> + }
> + } else
> + num_pages_from_user = get_user_pages(current, current->mm,
> vaddr & PAGE_MASK,
> buf->num_pages,
> write,
> @@ -201,8 +226,9 @@ userptr_fail_alloc_table_from_pages:
> userptr_fail_get_user_pages:
> dprintk(1, "get_user_pages requested/got: %d/%d]\n",
> num_pages_from_user, buf->num_pages);
> - while (--num_pages_from_user >= 0)
> - put_page(buf->pages[num_pages_from_user]);
> + if (!vma_is_io(buf->vma))
> + while (--num_pages_from_user >= 0)
> + put_page(buf->pages[num_pages_from_user]);
> kfree(buf->pages);
> kfree(buf);
> return NULL;
> @@ -225,7 +251,8 @@ static void vb2_dma_sg_put_userptr(void *buf_priv)
> while (--i >= 0) {
> if (buf->write)
> set_page_dirty_lock(buf->pages[i]);
> - put_page(buf->pages[i]);
> + if (!vma_is_io(buf->vma))
> + put_page(buf->pages[i]);
> }
> kfree(buf->pages);
> kfree(buf);

Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland