On Wed, Mar 23, 2022 at 08:54:08PM +0000, Robin Murphy wrote:
I'll admit I still never quite grasped the reason for also adding the override to swiotlb_sync_single_for_device() in aa6f8dcbab47, but I think by that point we were increasingly tired and confused and starting to second-guess ourselves (well, I was, at least). I don't think it's wrong per se, but as I said I do think it can bite anyone who's been doing dma_sync_*() wrong but getting away with it until now. If ddbd89deb7d3 alone turns out to work OK then I'd be inclined to try a partial revert of just that one hunk.
Agreed. Let's try that first.
Oleksandr, can you try the patch below:
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index 6db1c475ec827..6c350555e5a1c 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -701,13 +701,10 @@ void swiotlb_tbl_unmap_single(struct device *dev, phys_addr_t tlb_addr, void swiotlb_sync_single_for_device(struct device *dev, phys_addr_t tlb_addr, size_t size, enum dma_data_direction dir) { - /* - * Unconditional bounce is necessary to avoid corruption on - * sync_*_for_cpu or dma_ummap_* when the device didn't overwrite - * the whole lengt of the bounce buffer. - */ - swiotlb_bounce(dev, tlb_addr, size, DMA_TO_DEVICE); - BUG_ON(!valid_dma_direction(dir)); + if (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL) + swiotlb_bounce(dev, tlb_addr, size, DMA_TO_DEVICE); + else + BUG_ON(dir != DMA_FROM_DEVICE); }
void swiotlb_sync_single_for_cpu(struct device *dev, phys_addr_t tlb_addr,