Messages in this thread | | | Subject | Re: [RFC PATCH] arm64: mm: Add invalidate back in arch_sync_dma_for_device when FROM_DEVICE | From | Nanyong Sun <> | Date | Sun, 20 Nov 2022 10:58:40 +0800 |
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On 2022/11/17 18:23, Robin Murphy wrote:
> On 2022-11-17 08:24, Ard Biesheuvel wrote: >> On Thu, 17 Nov 2022 at 07:33, Nanyong Sun <sunnanyong@huawei.com> wrote: >>> >>> The commit c50f11c6196f ("arm64: mm: Don't invalidate FROM_DEVICE >>> buffers at start of DMA transfer") replaces invalidate with clean >>> when DMA_FROM_DEVICE, this changes the behavior of functions like >>> dma_map_single() and dma_sync_single_for_device(*, *, *, >>> DMA_FROM_DEVICE), >>> then it may make some drivers works unwell because the implementation >>> of these DMA APIs lose the original cache invalidation. >>> >>> Situation 1: >> ... >>> Situation 2: >>> After backporting the above commit, we find a network card driver go >>> wrong with cache inconsistency when doing DMA transfer: CPU got the >>> stale data in cache when reading DMA data received from device. >> >> I suppose this means those drivers may lack dma_sync_single_for_cpu() >> calls after the inbound transfers complete, and are instead relying on >> the cache invalidation performed before the transfer to make the DMA'd >> data visible to the CPU. > > It also commonly goes wrong the other way round when the drivers are > correct but DT/ACPI failed to indicate a coherent device as such. If > writes from the device actually snoop, they hit the still-present > cache line, which then gets invalidated by unmap/sync_for_cpu and the > new data is lost. > > Robin. > > . Is it acceptable? Does the coherent device MUST run with coherent identifier? At least they can run with no wrong before.
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