linux-kernel - Re: [PATCH 2/2] swiotlb: Skip cache maintenance on map error

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Message-ID: <20181120144943.GI10917@char.us.oracle.com>
Date:   Tue, 20 Nov 2018 09:49:43 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Robin Murphy <robin.murphy@....com>, sstabellini@...nel.org
Cc:     hch@....de, m.szyprowski@...sung.com, john.stultz@...aro.org,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] swiotlb: Skip cache maintenance on map error

On Tue, Nov 20, 2018 at 02:09:53PM +0000, 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.

+Stefano
> 
> Fixes: a4a4330db46a ("swiotlb: add support for non-coherent DMA")
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
>  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
>