SWIOTLB fixes for 4.20
Robin Murphy
reviewerv2 cover SWIOTLB fixes for 4.20
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(-)
Signature · 1 line
2.19.1.dirty
Robin Murphy
reviewerPATCH v2 1/2 dma-direct: Make DIRECT_MAPPING_ERROR viable for SWIOTLB
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.
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v2: Add parentheses, tweak commit message, collect tags
include/linux/dma-direct.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
include/linux/dma-direct.h +1 -1
@@ -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>
Signature · 1 line
2.19.1.dirty
Robin Murphy
reviewerPATCH v2 2/2 swiotlb: Skip cache maintenance on map error
In reply to Robin MurphyIf 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.
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v2: Collect tags
kernel/dma/swiotlb.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
kernel/dma/swiotlb.c +2 -1
@@ -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;
Signature · 1 line
2.19.1.dirty
Re: [PATCH v2 2/2] swiotlb: Skip cache maintenance on map error
Quoted 11 lines · Robin Murphy
If
swiotlb_bounce_page()failed, callingarch_sync_dma_for_device()may lead to such delights as performing cache maintenance on whatever addressphys_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 <[email protected]>Reviewed-by Christoph Hellwig <[email protected]>Signed-off-by Robin Murphy <[email protected]>
Quoted 24 lines
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v2: Collect tags
kernel/dma/swiotlb.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)kernel/dma/swiotlb.c +2
-1@@ -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;Signature · 1 line
2.19.1.dirty
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.