Messages in this thread | | | Date | Tue, 14 Aug 2018 09:35:01 +0100 | From | Will Deacon <> | Subject | Re: [PATCH v3 4/6] iommu/io-pgtable-arm: add support for non-strict mode |
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On Tue, Aug 14, 2018 at 04:33:41PM +0800, Leizhen (ThunderTown) wrote: > On 2018/8/6 9:32, Yang, Shunyong wrote: > > On 2018/7/26 22:37, Robin Murphy wrote: > >> Because DMA code is not the only caller of iommu_map/unmap. It's > >> perfectly legal in the IOMMU API to partially unmap a previous mapping > >> such that a block entry needs to be split. The DMA API, however, is a > >> lot more constrined, and thus by construction the iommu-dma layer will > >> never generate a block-splitting iommu_unmap() except as a result of > >> illegal DMA API usage, and we obviously do not need to optimise for that > >> (you will get a warning about mismatched unmaps under dma-debug, but > >> it's a bit too expensive to police in the general case). > >> > > > > When I was reading the code around arm_lpae_split_blk_unmap(), I was > > curious in which scenario a block will be split. Now with your comments > > "Because DMA code is not the only caller of iommu_map/unmap", it seems > > depending on the user. > > > > Would you please explain this further? I mean besides DMA, which user > > will use iommu_map/umap and how it split a block. > > I also think that arm_lpae_split_blk_unmap() scenario is not exist, maybe > we should remove it, and give a warning for this wrong usage.
Can't it happen with VFIO?
Will
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