Messages in this thread | | | Date | Wed, 6 Feb 2019 23:31:04 -0800 | From | Christoph Hellwig <> | Subject | Re: [Linaro-mm-sig] [PATCH 2/4] staging: android: ion: Restrict cache maintenance to dma mapped memory |
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The CPU may only access DMA mapped memory if ownership has been transferred back to the CPU using dma_sync_{single,sg}_to_cpu, and then before the device can access it again ownership needs to be transferred back to the device using dma_sync_{single,sg}_to_device.
> I've run some testing, and this patch does indeed fix the crash in > dma_sync_sg_for_cpu when it tried to use the 0 dma_address from the sg > list. > > Tested-by: Ørjan Eide <orjan.eide@arm.com> > > I tested this on an older kernel, v4.14, since the dma-mapping code > moved, in v4.19, to ignore the dma_address and instead use sg_phys() to > get a valid address from the page, which is always valid in the ion sg > lists. While this wouldn't crash on newer kernels, it's still good to > avoid the unnecessary work when no CMO is needed.
Can you also test is with CONFIG_DMA_API_DEBUG enabled, as that should catch all the usual mistakes in DMA API usage, including the one found?
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