[PATCH v2 0/2] SWIOTLB fixes for 4.20

[PATCH v2 0/2] SWIOTLB fixes for 4.20

[Robin Murphy]

Here's a quick v2 addressing Christoph's nits and collecting the tags
given so far. I've reproduced my USB problem with a commit prior to the
dma-mapping pull, so it looks like the cache maintenance changes are off
the hook for that one (and I'll have to venture into USB/UAS territory).

No objection from me if Konrad wants to pick this up instead depending
on timing.

Robin.


Robin Murphy (2):
  dma-direct: Make DIRECT_MAPPING_ERROR viable for SWIOTLB
  swiotlb: Skip cache maintenance on map error

 include/linux/dma-direct.h | 2 +-
 kernel/dma/swiotlb.c       | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

-- 
2.19.1.dirty

[PATCH v2 1/2] dma-direct: Make DIRECT_MAPPING_ERROR viable for SWIOTLB

[Robin Murphy]

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
other commonly-used error value of all-bits-set, since the last single
byte of memory is by far the least-likely-valid DMA target.

Fixes: dff8d6c1ed58 ("swiotlb: remove the overflow buffer")
Reported-by: John Stultz <john.stultz@linaro.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---

v2: Add parentheses, tweak commit message, collect tags

 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..9e66bfe369aa 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

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

[Robin Murphy]

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@linaro.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---

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

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@linaro.org>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>

Acked-by: Stefano Stabellini <sstabellini@kernel.org>

> ---
> 
> 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
> 

Re: [PATCH v2 0/2] SWIOTLB fixes for 4.20

[Christoph Hellwig]

Thanks,

aplied to the dma-mapping for-linus tree.

I'll wait a little longer for a review from Stefano, but I really want
it in linux-next asap and hopefully off to Linus for the weekend.