On Wed, May 10, 2023 at 04:55:25PM +0800, Ruihan Li wrote:
> When hcd->localmem_pool is non-null, it is used to allocate DMA memory.
> In this case, the dma address will be properly returned (in dma_handle),
> and dma_mmap_coherent should be used to map this memory into the user
> space. However, the current implementation uses pfn_remap_range, which
> is supposed to map normal pages (instead of DMA pages).
>
> Instead of repeating the logic in the memory allocation function, this
> patch introduces a more robust solution. To address the previous issue,
> this patch checks the type of allocated memory by testing whether
> dma_handle is properly set. If dma_handle is properly returned, it means
> some DMA pages are allocated and dma_mmap_coherent should be used to map
> them. Otherwise, normal pages are allocated and pfn_remap_range should
> be called. This ensures that the correct mmap functions are used
> consistently, independently with logic details that determine which type
> of memory gets allocated.
>
> Fixes: a0e710a7def4 ("USB: usbfs: fix mmap dma mismatch")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Ruihan Li <lrh2000@xxxxxxxxxx>
> ---
> drivers/usb/core/devio.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
> index b4cf9e860..5067030b7 100644
> --- a/drivers/usb/core/devio.c
> +++ b/drivers/usb/core/devio.c
> @@ -235,7 +235,7 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
> size_t size = vma->vm_end - vma->vm_start;
> void *mem;
> unsigned long flags;
> - dma_addr_t dma_handle;
> + dma_addr_t dma_handle = DMA_MAPPING_ERROR;
> int ret;
>
> ret = usbfs_increase_memory_usage(size + sizeof(struct usb_memory));
> @@ -265,7 +265,13 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
> usbm->vma_use_count = 1;
> INIT_LIST_HEAD(&usbm->memlist);
>
> - if (hcd->localmem_pool || !hcd_uses_dma(hcd)) {
> + /* In DMA-unavailable cases, hcd_buffer_alloc_pages allocates
> + * normal pages and assigns DMA_MAPPING_ERROR to dma_handle. Check
> + * whether we are in such cases, and then use remap_pfn_range (or
> + * dma_mmap_coherent) to map normal (or DMA) pages into the user
> + * space, respectively.
> + */
Another stylistic issue. For multi-line comments, the format we use is:
/*
* Blah, blah, blah
* Blah, blah, blah
*/
Alan Stern
