Re: [PATCH] ion: scatterlist offset not used for buffer map

[Laura Abbott]

On 04/07/2016 04:29 AM, John Einar Reitan wrote:
> ion's default user/kernel page mapping code don't honor the offset
> option for scatterlists. It uses sg_page and expect the whole page to be
> mapped, while the offset could dictate an offset within a large page.
>
> sg_phys correctly accounts for the offset, so should be used instead.

Can you be more specific about which heap and which allocation pattern
is exposing this bug?

> Signed-off-by: John Einar Reitan <john.reitan@xxxxxxxxxxxx>
> ---
>   drivers/staging/android/ion/ion_heap.c | 11 +++++------
>   1 file changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/staging/android/ion/ion_heap.c b/drivers/staging/android/ion/ion_heap.c
> index ca15a87..e83002dc 100644
> --- a/drivers/staging/android/ion/ion_heap.c
> +++ b/drivers/staging/android/ion/ion_heap.c
> @@ -47,7 +47,7 @@ void *ion_heap_map_kernel(struct ion_heap *heap,
>
>   	for_each_sg(table->sgl, sg, table->nents, i) {
>   		int npages_this_entry = PAGE_ALIGN(sg->length) / PAGE_SIZE;
> -		struct page *page = sg_page(sg);
> +		struct page *page = pfn_to_page(PFN_DOWN(sg_phys(sg)));
>   
>   		BUG_ON(i >= npages);
>   		for (j = 0; j < npages_this_entry; j++)
> @@ -79,7 +79,6 @@ int ion_heap_map_user(struct ion_heap *heap, struct ion_buffer *buffer,
>   	int ret;
>
>   	for_each_sg(table->sgl, sg, table->nents, i) {
> -		struct page *page = sg_page(sg);
>   		unsigned long remainder = vma->vm_end - addr;
>   		unsigned long len = sg->length;
>
> @@ -87,18 +86,18 @@ int ion_heap_map_user(struct ion_heap *heap, struct ion_buffer *buffer,
>   			offset -= sg->length;
>   			continue;
>   		} else if (offset) {
> -			page += offset / PAGE_SIZE;
>   			len = sg->length - offset;
> -			offset = 0;
>   		}
>   		len = min(len, remainder);
> -		ret = remap_pfn_range(vma, addr, page_to_pfn(page), len,
> -				vma->vm_page_prot);
> +		ret = remap_pfn_range(vma, addr, PFN_DOWN(sg_phys(sg) + offset),
> +				      len, vma->vm_page_prot);
>   		if (ret)
>   			return ret;
>   		addr += len;
>   		if (addr >= vma->vm_end)
>   			return 0;
> +
> +		offset = 0;
>   	}
>   	return 0;
>   }