Messages in this thread | | | Date | Thu, 17 Nov 2022 10:23:13 +0000 | Subject | Re: [RFC PATCH] arm64: mm: Add invalidate back in arch_sync_dma_for_device when FROM_DEVICE | From | Robin Murphy <> |
| |
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.
| |