Re: [PATCH v2 2/2] swiotlb: Skip cache maintenance on map error

[Stefano Stabellini]

On Wed, 21 Nov 2018, Robin Murphy wrote:
> If swiotlb_bounce_page() failed, calling arch_sync_dma_for_device() may
> lead to such delights as performing cache maintenance on whatever
> address phys_to_virt(SWIOTLB_MAP_ERROR) looks like, which is typically
> outside the kernel memory map and goes about as well as expected.
> 
> Don't do that.
> 
> Fixes: a4a4330db46a ("swiotlb: add support for non-coherent DMA")
> Tested-by: John Stultz <john.stultz@xxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>

Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

> ---
> 
> v2: Collect tags
> 
>  kernel/dma/swiotlb.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 5731daa09a32..045930e32c0e 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -679,7 +679,8 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
>  	}
>  
>  	if (!dev_is_dma_coherent(dev) &&
> -	    (attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
> +	    (attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0 &&
> +	    dev_addr != DIRECT_MAPPING_ERROR)
>  		arch_sync_dma_for_device(dev, phys, size, dir);
>  
>  	return dev_addr;
> -- 
> 2.19.1.dirty
>