From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: hch@lst.de, m.szyprowski@samsung.com, john.stultz@linaro.org,
iommu@lists.linux-foundation.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] swiotlb: Make DIRECT_MAPPING_ERROR viable
Date: Tue, 20 Nov 2018 09:49:18 -0500 [thread overview]
Message-ID: <20181120144918.GH10917@char.us.oracle.com> (raw)
In-Reply-To: <e90da5fbab881c502ac3412fb05c44b26c99f73a.1542722463.git.robin.murphy@arm.com>
On Tue, Nov 20, 2018 at 02:09:52PM +0000, Robin Murphy wrote:
> With the overflow buffer removed, we no longer have a unique address
> which is guaranteed not to be a valid DMA target to use as an error
> token. The DIRECT_MAPPING_ERROR value of 0 tries to at least represent
> an unlikely DMA target, but unfortunately there are already SWIOTLB
> users with DMA-able memory at physical address 0 which now gets falsely
> treated as a mapping failure and leads to all manner of misbehaviour.
>
> The best we can do to mitigate that is flip DIRECT_MAPPING_ERROR to the
> commonly-used all-bits-set value, since the last single byte of memory
> is by far the least-likely-valid DMA target.
Are all the callers checking for DIRECT_MAPPING_ERROR or is it more of
a comparison (as in if (!ret)) ?
>
> Fixes: dff8d6c1ed58 ("swiotlb: remove the overflow buffer")]
> Reported-by: John Stultz <john.stultz@linaro.org>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
> include/linux/dma-direct.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
> index bd73e7a91410..9de9c7ab39d6 100644
> --- a/include/linux/dma-direct.h
> +++ b/include/linux/dma-direct.h
> @@ -5,7 +5,7 @@
> #include <linux/dma-mapping.h>
> #include <linux/mem_encrypt.h>
>
> -#define DIRECT_MAPPING_ERROR 0
> +#define DIRECT_MAPPING_ERROR ~(dma_addr_t)0
>
> #ifdef CONFIG_ARCH_HAS_PHYS_TO_DMA
> #include <asm/dma-direct.h>
> --
> 2.19.1.dirty
>
next prev parent reply other threads:[~2018-11-20 14:49 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-20 14:09 [PATCH 0/2] SWIOTLB fixes for 4.20 Robin Murphy
2018-11-20 14:09 ` [PATCH 1/2] swiotlb: Make DIRECT_MAPPING_ERROR viable Robin Murphy
2018-11-20 14:49 ` Konrad Rzeszutek Wilk [this message]
2018-11-20 15:01 ` Robin Murphy
2018-11-20 16:34 ` Konrad Rzeszutek Wilk
2018-11-20 16:07 ` Christoph Hellwig
2018-11-20 14:09 ` [PATCH 2/2] swiotlb: Skip cache maintenance on map error Robin Murphy
2018-11-20 14:49 ` Konrad Rzeszutek Wilk
2018-11-20 16:07 ` Christoph Hellwig
2018-11-20 16:08 ` [PATCH 0/2] SWIOTLB fixes for 4.20 Christoph Hellwig
2018-11-20 16:34 ` Konrad Rzeszutek Wilk
2018-11-21 13:03 ` Christoph Hellwig
2018-11-21 15:11 ` Konrad Rzeszutek Wilk
2018-11-27 19:07 ` Stefano Stabellini
2018-11-27 20:39 ` Stefano Stabellini
2018-11-20 19:24 ` John Stultz
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