Messages in this thread | | | Subject | Re: [PATCH v3 2/5] dma-iommu: fix arch_sync_dma for map | From | Robin Murphy <> | Date | Thu, 12 Aug 2021 11:38:02 +0100 |
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On 2021-08-12 10:21, David Stevens wrote: > On Thu, Aug 12, 2021 at 3:47 AM Robin Murphy <robin.murphy@arm.com> wrote: >> >> On 2021-08-11 03:42, David Stevens wrote: >>> From: David Stevens <stevensd@chromium.org> >>> >>> When calling arch_sync_dma, we need to pass it the memory that's >>> actually being used for dma. When using swiotlb bounce buffers, this is >>> the bounce buffer. Move arch_sync_dma into the __iommu_dma_map_swiotlb >>> helper, so it can use the bounce buffer address if necessary. This also >>> means it is no longer necessary to call iommu_dma_sync_sg_for_device in >>> iommu_dma_map_sg for untrusted devices. >>> >>> Fixes: 82612d66d51d ("iommu: Allow the dma-iommu api to use bounce buffers") >>> Signed-off-by: David Stevens <stevensd@chromium.org> >>> --- >>> drivers/iommu/dma-iommu.c | 16 +++++++--------- >>> 1 file changed, 7 insertions(+), 9 deletions(-) >>> >>> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c >>> index 54e103b989d9..4f0cc4a0a61f 100644 >>> --- a/drivers/iommu/dma-iommu.c >>> +++ b/drivers/iommu/dma-iommu.c >>> @@ -576,6 +576,9 @@ static dma_addr_t __iommu_dma_map_swiotlb(struct device *dev, phys_addr_t phys, >>> memset(padding_start, 0, padding_size); >>> } >>> >>> + if (!coherent && !(attrs & DMA_ATTR_SKIP_CPU_SYNC)) >> >> Make that an "else if" - otherwise you're just reintroducing the same >> thing that the third hunk is trying to clean up. > > swiotlb_tbl_map_single only copies into the swiotlb buffer, it doesn't > do any architectural syncing. So this block is necessary in the > swiotlb case as well, for iommu_dma_map_page to work properly.
Urgh, apologies again - I had a mental short-circuit and was convinced that the SWIOTLB call already did its own cache maintenance. I really should have learned by now not to review fiddly patches like these while tired... > The third chunk is a separate optimization, so I'll split it out into > its own patch.
It's still a logical part of this change - cleaning up the potentially wrong sync while you make sure the right one happens. Even more so if you make the fix the better way by having iommu_dma_map_sg_swiotlb() call iommu_dma_map_page().
Robin.
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