Re: [PATCH v2] dma-mapping: use vmalloc_to_page for vmalloc addresses

From: Stefano Stabellini
Date: Tue Jul 13 2021 - 21:23:59 EST


On Tue, 22 Jun 2021, Roman Skakun wrote:
> This commit is dedicated to fix incorrect conversion from
> cpu_addr to page address in cases when we get virtual
> address which allocated in the vmalloc range.
> As the result, virt_to_page() cannot convert this address
> properly and return incorrect page address.
>
> Need to detect such cases and obtains the page address using
> vmalloc_to_page() instead.
>
> Signed-off-by: Roman Skakun <roman_skakun@xxxxxxxx>
> Reviewed-by: Andrii Anisov <andrii_anisov@xxxxxxxx>
> ---
> Hey!
> Thanks for suggestions, Christoph!
> I updated the patch according to your advice.
> But, I'm so surprised because nobody catches this problem
> in the common code before. It looks a bit strange as for me.
>
>
> kernel/dma/ops_helpers.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/dma/ops_helpers.c b/kernel/dma/ops_helpers.c
> index 910ae69cae77..782728d8a393 100644
> --- a/kernel/dma/ops_helpers.c
> +++ b/kernel/dma/ops_helpers.c
> @@ -5,6 +5,14 @@
> */
> #include <linux/dma-map-ops.h>
>
> +static struct page *cpu_addr_to_page(void *cpu_addr)
> +{
> + if (is_vmalloc_addr(cpu_addr))
> + return vmalloc_to_page(cpu_addr);
> + else
> + return virt_to_page(cpu_addr);
> +}

We have the same thing in xen_swiotlb_free_coherent. Can we find a way
to call cpu_addr_to_page() from xen_swiotlb_free_coherent? Maybe we can
make cpu_addr_to_page non-static? No problem if it is too much trouble.


> /*
> * Create scatter-list for the already allocated DMA buffer.
> */
> @@ -12,7 +20,7 @@ int dma_common_get_sgtable(struct device *dev, struct sg_table *sgt,
> void *cpu_addr, dma_addr_t dma_addr, size_t size,
> unsigned long attrs)
> {
> - struct page *page = virt_to_page(cpu_addr);
> + struct page *page = cpu_addr_to_page(cpu_addr);
> int ret;
>
> ret = sg_alloc_table(sgt, 1, GFP_KERNEL);
> @@ -43,7 +51,7 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
> return -ENXIO;
>
> return remap_pfn_range(vma, vma->vm_start,
> - page_to_pfn(virt_to_page(cpu_addr)) + vma->vm_pgoff,
> + page_to_pfn(cpu_addr_to_page(cpu_addr)) + vma->vm_pgoff,
> user_count << PAGE_SHIFT, vma->vm_page_prot);
> #else
> return -ENXIO;
> --
> 2.25.1
>