>From the DMA point of view this looks good:
Reviewed-by: Christoph Hellwig <h...@lst.de>
I still think that doing that SetPageReserved + remap_pfn_range
dance for the normal memory allocations is a bad idea. Just use
vm_insert_page on the page, in which case it doesn't need to be
marked as Reserved.
On Tue, Jun 25, 2019 at 12:26:59PM +0100, Ian Abbott wrote:
> Comedi's acquisition buffer allocation code can allocate the buffer from
> normal kernel memory or from DMA coherent memory depending on the
> `dma_async_dir` value in the comedi subdevice. (A value of `DMA_NONE`
> causes the buffer to be allocated from normal kernel memory. Other
> values cause the buffer to be allocated from DMA coherent memory.) The
> buffer currently consists of a bunch of page-sized blocks that are
> vmap'ed into a contiguous range of virtual addresses. The pages are also
> mmap'able into user address space. For DMA'able buffers, these
> page-sized blocks are allocated by `dma_alloc_coherent()`.
>
> For DMA-able buffers, the DMA API is currently abused in various ways,
> the most serious abuse being the calling of `virt_to_page()` on the
> blocks allocated by `dma_alloc_coherent()` and passing those pages to
> `vmap()` (for mapping to the kernels vmalloc address space) and via
> `page_to_pfn()` to `remap_pfn_range()` (for mmap'ing to user space). it
> also uses the `__GFP_COMP` flag when allocating the blocks, and marks
> the allocated pages as reserved (which is unnecessary for DMA coherent
> allocations).
>
> The code can be changed to get rid of the vmap'ed address altogether if
> necessary, since there are only a few places in the comedi code that use
> the vmap'ed address directly and we also keep a list of the kernel
> addresses for the individual pages prior to the vmap operation. This
> would add some run-time overhead to buffer accesses. The real killer is
> the mmap operation.
>
> For mmap, the address range specified in the VMA needs to be mmap'ed to
> the individually allocated page-sized blocks. That is not a problem
> when the pages are allocated from normal kernel memory as the individual
> pages can be remapped by `remap_pfn_range()`, but it is a problem when
> the page-sized blocks are allocated by `dma_alloc_coherent()` because
> the DMA API currently has no support for splitting a VMA across multiple
> blocks of DMA coherent memory (or rather, no support for mapping part of
> a VMA range to a single block of DMA coherent memory).
>
> In order to comply with the DMA API and allow the buffer to be mmap'ed,
> the buffer needs to be allocated as a single block by a single call to
> `dma_alloc_coherent()`, freed by a single call to `dma_free_coherent()`,
> and mmap'ed to user space by a single call to `dma_mmap_coherent()`.
> This patch changes the buffer allocation, freeing, and mmap'ing code to
> do that, with the unfortunate consequence that buffer allocation is more
> likely to fail. It also no longer uses the `__GFP_COMP` flag when
> allocating DMA coherent memory, no longer marks the
> allocated pages of DMA coherent memory as reserved, and no longer vmap's
> the DMA coherent memory pages (since they are contiguous anyway).
>
> Cc: Christoph Hellwig <h...@lst.de>
> Signed-off-by: Ian Abbott <abbo...@mev.co.uk>
> ---
> drivers/staging/comedi/comedi_buf.c | 150 ++++++++++++++++++---------
> drivers/staging/comedi/comedi_fops.c | 39 ++++---
> 2 files changed, 125 insertions(+), 64 deletions(-)
>
> diff --git a/drivers/staging/comedi/comedi_buf.c
> b/drivers/staging/comedi/comedi_buf.c
> index d2c8cc72a99d..3ef3ddabf139 100644
> --- a/drivers/staging/comedi/comedi_buf.c
> +++ b/drivers/staging/comedi/comedi_buf.c
> @@ -27,18 +27,19 @@ static void comedi_buf_map_kref_release(struct kref *kref)
> unsigned int i;
>
> if (bm->page_list) {
> - for (i = 0; i < bm->n_pages; i++) {
> - buf = &bm->page_list[i];
> - clear_bit(PG_reserved,
> - &(virt_to_page(buf->virt_addr)->flags));
> - if (bm->dma_dir != DMA_NONE) {
> -#ifdef CONFIG_HAS_DMA
> - dma_free_coherent(bm->dma_hw_dev,
> - PAGE_SIZE,
> - buf->virt_addr,
> - buf->dma_addr);
> -#endif
> - } else {
> + if (bm->dma_dir != DMA_NONE) {
> + /*
> + * DMA buffer was allocated as a single block.
> + * Address is in page_list[0].
> + */
> + buf = &bm->page_list[0];
> + dma_free_coherent(bm->dma_hw_dev,
> + PAGE_SIZE * bm->n_pages,
> + buf->virt_addr, buf->dma_addr);
> + } else {
> + for (i = 0; i < bm->n_pages; i++) {
> + buf = &bm->page_list[i];
> + ClearPageReserved(virt_to_page(buf->virt_addr));
> free_page((unsigned long)buf->virt_addr);
> }
> }
> @@ -57,7 +58,8 @@ static void __comedi_buf_free(struct comedi_device *dev,
> unsigned long flags;
>
> if (async->prealloc_buf) {
> - vunmap(async->prealloc_buf);
> + if (s->async_dma_dir == DMA_NONE)
> + vunmap(async->prealloc_buf);
> async->prealloc_buf = NULL;
> async->prealloc_bufsz = 0;
> }
> @@ -69,6 +71,72 @@ static void __comedi_buf_free(struct comedi_device *dev,
> comedi_buf_map_put(bm);
> }
>
> +static struct comedi_buf_map *
> +comedi_buf_map_alloc(struct comedi_device *dev, enum dma_data_direction
> dma_dir,
> + unsigned int n_pages)
> +{
> + struct comedi_buf_map *bm;
> + struct comedi_buf_page *buf;
> + unsigned int i;
> +
> + bm = kzalloc(sizeof(*bm), GFP_KERNEL);
> + if (!bm)
> + return NULL;
> +
> + kref_init(&bm->refcount);
> + bm->dma_dir = dma_dir;
> + if (bm->dma_dir != DMA_NONE) {
> + /* Need ref to hardware device to free buffer later. */
> + bm->dma_hw_dev = get_device(dev->hw_dev);
> + }
> +
> + bm->page_list = vzalloc(sizeof(*buf) * n_pages);
> + if (!bm->page_list)
> + goto err;
> +
> + if (bm->dma_dir != DMA_NONE) {
> + void *virt_addr;
> + dma_addr_t dma_addr;
> +
> + /*
> + * Currently, the DMA buffer needs to be allocated as a
> + * single block so that it can be mmap()'ed.
> + */
> + virt_addr = dma_alloc_coherent(bm->dma_hw_dev,
> + PAGE_SIZE * n_pages, &dma_addr,
> + GFP_KERNEL);
> + if (!virt_addr)
> + goto err;
> +
> + for (i = 0; i < n_pages; i++) {
> + buf = &bm->page_list[i];
> + buf->virt_addr = virt_addr + (i << PAGE_SHIFT);
> + buf->dma_addr = dma_addr + (i << PAGE_SHIFT);
> + }
> +
> + bm->n_pages = i;
> + } else {
> + for (i = 0; i < n_pages; i++) {
> + buf = &bm->page_list[i];
> + buf->virt_addr = (void *)get_zeroed_page(GFP_KERNEL);
> + if (!buf->virt_addr)
> + break;
> +
> + SetPageReserved(virt_to_page(buf->virt_addr));
> + }
> +
> + bm->n_pages = i;
> + if (i < n_pages)
> + goto err;
> + }
> +
> + return bm;
> +
> +err:
> + comedi_buf_map_put(bm);
> + return NULL;
> +}
> +
> static void __comedi_buf_alloc(struct comedi_device *dev,
> struct comedi_subdevice *s,
> unsigned int n_pages)
> @@ -86,57 +154,37 @@ static void __comedi_buf_alloc(struct comedi_device *dev,
> return;
> }
>
> - bm = kzalloc(sizeof(*async->buf_map), GFP_KERNEL);
> + bm = comedi_buf_map_alloc(dev, s->async_dma_dir, n_pages);
> if (!bm)
> return;
>
> - kref_init(&bm->refcount);
> spin_lock_irqsave(&s->spin_lock, flags);
> async->buf_map = bm;
> spin_unlock_irqrestore(&s->spin_lock, flags);
> - bm->dma_dir = s->async_dma_dir;
> - if (bm->dma_dir != DMA_NONE)
> - /* Need ref to hardware device to free buffer later. */
> - bm->dma_hw_dev = get_device(dev->hw_dev);
>
> - bm->page_list = vzalloc(sizeof(*buf) * n_pages);
> - if (bm->page_list)
> + if (bm->dma_dir != DMA_NONE) {
> + /*
> + * DMA buffer was allocated as a single block.
> + * Address is in page_list[0].
> + */
> + buf = &bm->page_list[0];
> + async->prealloc_buf = buf->virt_addr;
> + } else {
> pages = vmalloc(sizeof(struct page *) * n_pages);
> + if (!pages)
> + return;
>
> - if (!pages)
> - return;
> -
> - for (i = 0; i < n_pages; i++) {
> - buf = &bm->page_list[i];
> - if (bm->dma_dir != DMA_NONE)
> -#ifdef CONFIG_HAS_DMA
> - buf->virt_addr = dma_alloc_coherent(bm->dma_hw_dev,
> - PAGE_SIZE,
> - &buf->dma_addr,
> - GFP_KERNEL |
> - __GFP_COMP);
> -#else
> - break;
> -#endif
> - else
> - buf->virt_addr = (void *)get_zeroed_page(GFP_KERNEL);
> - if (!buf->virt_addr)
> - break;
> -
> - set_bit(PG_reserved, &(virt_to_page(buf->virt_addr)->flags));
> -
> - pages[i] = virt_to_page(buf->virt_addr);
> - }
> - spin_lock_irqsave(&s->spin_lock, flags);
> - bm->n_pages = i;
> - spin_unlock_irqrestore(&s->spin_lock, flags);
> + for (i = 0; i < n_pages; i++) {
> + buf = &bm->page_list[i];
> + pages[i] = virt_to_page(buf->virt_addr);
> + }
>
> - /* vmap the prealloc_buf if all the pages were allocated */
> - if (i == n_pages)
> + /* vmap the pages to prealloc_buf */
> async->prealloc_buf = vmap(pages, n_pages, VM_MAP,
> COMEDI_PAGE_PROTECTION);
>
> - vfree(pages);
> + vfree(pages);
> + }
> }
>
> void comedi_buf_map_get(struct comedi_buf_map *bm)
> diff --git a/drivers/staging/comedi/comedi_fops.c
> b/drivers/staging/comedi/comedi_fops.c
> index f6d1287c7b83..08d1bbbebf2d 100644
> --- a/drivers/staging/comedi/comedi_fops.c
> +++ b/drivers/staging/comedi/comedi_fops.c
> @@ -2301,11 +2301,12 @@ static int comedi_mmap(struct file *file, struct
> vm_area_struct *vma)
> struct comedi_subdevice *s;
> struct comedi_async *async;
> struct comedi_buf_map *bm = NULL;
> + struct comedi_buf_page *buf;
> unsigned long start = vma->vm_start;
> unsigned long size;
> int n_pages;
> int i;
> - int retval;
> + int retval = 0;
>
> /*
> * 'trylock' avoids circular dependency with current->mm->mmap_sem
> @@ -2361,24 +2362,36 @@ static int comedi_mmap(struct file *file, struct
> vm_area_struct *vma)
> retval = -EINVAL;
> goto done;
> }
> - for (i = 0; i < n_pages; ++i) {
> - struct comedi_buf_page *buf = &bm->page_list[i];
> + if (bm->dma_dir != DMA_NONE) {
> + /*
> + * DMA buffer was allocated as a single block.
> + * Address is in page_list[0].
> + */
> + buf = &bm->page_list[0];
> + retval = dma_mmap_coherent(bm->dma_hw_dev, vma, buf->virt_addr,
> + buf->dma_addr, n_pages * PAGE_SIZE);
> + } else {
> + for (i = 0; i < n_pages; ++i) {
> + unsigned long pfn;
> +
> + buf = &bm->page_list[i];
> + pfn = page_to_pfn(virt_to_page(buf->virt_addr));
> + retval = remap_pfn_range(vma, start, pfn, PAGE_SIZE,
> + PAGE_SHARED);
> + if (retval)
> + break;
>
> - if (remap_pfn_range(vma, start,
> - page_to_pfn(virt_to_page(buf->virt_addr)),
> - PAGE_SIZE, PAGE_SHARED)) {
> - retval = -EAGAIN;
> - goto done;
> + start += PAGE_SIZE;
> }
> - start += PAGE_SIZE;
> }
>
> - vma->vm_ops = &comedi_vm_ops;
> - vma->vm_private_data = bm;
> + if (retval == 0) {
> + vma->vm_ops = &comedi_vm_ops;
> + vma->vm_private_data = bm;
>
> - vma->vm_ops->open(vma);
> + vma->vm_ops->open(vma);
> + }
>
> - retval = 0;
> done:
> up_read(&dev->attach_lock);
> comedi_buf_map_put(bm); /* put reference to buf map - okay if NULL */
> --
> 2.20.1
---end quoted text---
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