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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

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
>