linux-kernel - Re: [PATCH 4.19 105/306] swiotlb: do not panic on mapping failures

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Date:   Thu, 28 Nov 2019 22:20:08 +0100
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Robin Murphy <robin.murphy@....com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 105/306] swiotlb: do not panic on mapping failures

On Wed 2019-11-27 21:29:15, Greg Kroah-Hartman wrote:
> From: Christoph Hellwig <hch@....de>
> 
> [ Upstream commit 8088546832aa2c0d8f99dd56edf6384f8a9b63b3 ]
> 
> All properly written drivers now have error handling in the
> dma_map_single / dma_map_page callers.  As swiotlb_tbl_map_single already
> prints a useful warning when running out of swiotlb pool space we can
> also remove swiotlb_full entirely as it serves no purpose now.

Umm. I trust you that is true in mainline, but is it also true for
-stable kernels?

Does this fix anything for -stable users?

Best regards,
							Pavel

> +++ b/kernel/dma/swiotlb.c
> @@ -761,34 +761,6 @@ static bool swiotlb_free_buffer(struct device *dev, size_t size,
>  	return true;
>  }
>  
> -static void
> -swiotlb_full(struct device *dev, size_t size, enum dma_data_direction dir,
> -	     int do_panic)
> -{
> -	if (swiotlb_force == SWIOTLB_NO_FORCE)
> -		return;
> -
> -	/*
> -	 * Ran out of IOMMU space for this operation. This is very bad.
> -	 * Unfortunately the drivers cannot handle this operation properly.
> -	 * unless they check for dma_mapping_error (most don't)
> -	 * When the mapping is small enough return a static buffer to limit
> -	 * the damage, or panic when the transfer is too big.
> -	 */
> -	dev_err_ratelimited(dev, "DMA: Out of SW-IOMMU space for %zu bytes\n",
> -			    size);
> -
> -	if (size <= io_tlb_overflow || !do_panic)
> -		return;
> -
> -	if (dir == DMA_BIDIRECTIONAL)
> -		panic("DMA: Random memory could be DMA accessed\n");
> -	if (dir == DMA_FROM_DEVICE)
> -		panic("DMA: Random memory could be DMA written\n");
> -	if (dir == DMA_TO_DEVICE)
> -		panic("DMA: Random memory could be DMA read\n");
> -}
> -
>  /*
>   * Map a single buffer of the indicated size for DMA in streaming mode.  The
>   * physical address to use is returned.
> @@ -817,10 +789,8 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
>  
>  	/* Oh well, have to allocate and map a bounce buffer. */
>  	map = map_single(dev, phys, size, dir, attrs);
> -	if (map == SWIOTLB_MAP_ERROR) {
> -		swiotlb_full(dev, size, dir, 1);
> +	if (map == SWIOTLB_MAP_ERROR)
>  		return __phys_to_dma(dev, io_tlb_overflow_buffer);
> -	}
>  
>  	dev_addr = __phys_to_dma(dev, map);
>  
> @@ -954,7 +924,6 @@ swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl, int nelems,
>  			if (map == SWIOTLB_MAP_ERROR) {
>  				/* Don't panic here, we expect map_sg users
>  				   to do proper error handling. */
> -				swiotlb_full(hwdev, sg->length, dir, 0);
>  				attrs |= DMA_ATTR_SKIP_CPU_SYNC;
>  				swiotlb_unmap_sg_attrs(hwdev, sgl, i, dir,
>  						       attrs);

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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