Oh, I know, I've make a mistake, dmapool doesn't need to change. Huacai ------------------ Original ------------------ From: "Christoph Hellwig"<hch@xxxxxxxxxxxxx>; Date: Mon, Sep 18, 2017 11:51 PM To: "Robin Murphy"<robin.murphy@xxxxxxx>; Cc: "Huacai Chen"<chenhc@xxxxxxxxxx>; "Andrew Morton"<akpm@xxxxxxxxxxxxxxxxxxxx>; "Fuxin Zhang"<zhangfx@xxxxxxxxxx>; "linux-mm"<linux-mm@xxxxxxxxx>; "linux-kernel"<linux-kernel@xxxxxxxxxxxxxxx>; "stable"<stable@xxxxxxxxxxxxxxx>; Subject: Re: [V5, 2/3] mm: dmapool: Align to ARCH_DMA_MINALIGN innon-coherent DMA mode On Mon, Sep 18, 2017 at 10:44:54AM +0100, Robin Murphy wrote: > On 18/09/17 05:22, Huacai Chen wrote: > > In non-coherent DMA mode, kernel uses cache flushing operations to > > maintain I/O coherency, so the dmapool objects should be aligned to > > ARCH_DMA_MINALIGN. Otherwise, it will cause data corruption, at least > > on MIPS: > > > > Step 1, dma_map_single > > Step 2, cache_invalidate (no writeback) > > Step 3, dma_from_device > > Step 4, dma_unmap_single > > This is a massive red warning flag for the whole series, because DMA > pools don't work like that. At best, this will do nothing, and at worst > it is papering over egregious bugs elsewhere. Streaming mappings of > coherent allocations means completely broken code. Oh, I hadn't even seen that part. Yes, dma coherent (and pool) allocations must never be used for streaming mappings. I wish we'd have some debug infrastructure to warn on such uses.��.n������g��� �a��� �&ޖ)���)��h���&������梷���� �Ǟ�m������)������^�����������v���O��zf������
