Messages in this thread | | | Subject | Re: [PATCH v1 4/9] iommu/vt-d: Add bounce buffer API for domain map/unmap | From | Robin Murphy <> | Date | Tue, 19 Mar 2019 11:21:35 +0000 |
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On 19/03/2019 07:59, Lu Baolu wrote: > Hi Christoph, > > On 3/14/19 12:10 AM, Christoph Hellwig wrote: >> On Wed, Mar 13, 2019 at 10:31:52AM +0800, Lu Baolu wrote: >>> Hi again, >>> >>> On 3/13/19 10:04 AM, Lu Baolu wrote: >>>> Hi, >>>> >>>> On 3/13/19 12:38 AM, Christoph Hellwig wrote: >>>>> On Tue, Mar 12, 2019 at 02:00:00PM +0800, Lu Baolu wrote: >>>>>> This adds the APIs for bounce buffer specified domain >>>>>> map() and unmap(). The start and end partial pages will >>>>>> be mapped with bounce buffered pages instead. This will >>>>>> enhance the security of DMA buffer by isolating the DMA >>>>>> attacks from malicious devices. >>>>> >>>>> Please reuse the swiotlb code instead of reinventing it. >>>>> >>> >>> Just looked into the code again. At least we could reuse below >>> functions: >>> >>> swiotlb_tbl_map_single() >>> swiotlb_tbl_unmap_single() >>> swiotlb_tbl_sync_single() >>> >>> Anything else? >> >> Yes, that is probably about the level you want to reuse, given that the >> next higher layer already has hooks into the direct mapping code. >> > > I am trying to change my code to reuse swiotlb. But I found that swiotlb > might not be suitable for my case. > > Below is what I got with swiotlb_map(): > > phy_addr size tlb_addr > -------------------------------- > 0x167eec330 0x8 0x85dc6000 > 0x167eef5c0 0x40 0x85dc6800 > 0x167eec330 0x8 0x85dc7000 > 0x167eef5c0 0x40 0x85dc7800 > > But what I expected to get is: > > phy_addr size tlb_addr > -------------------------------- > 0x167eec330 0x8 0xAAAAA330 > 0x167eef5c0 0x40 0xBBBBB5c0 > 0x167eec330 0x8 0xCCCCC330 > 0x167eef5c0 0x40 0xDDDDD5c0 > > , where 0xXXXXXX000 is the physical address of a bounced page. > > Basically, I want a bounce page to replace a leaf page in the vt-d page > table, which maps a buffer with size less than a PAGE_SIZE.
I'd imagine the thing to do would be to factor out the slot allocation in swiotlb_tbl_map_single() so that an IOMMU page pool/allocator can be hooked in as an alternative.
However we implement it, though, this should absolutely be a common IOMMU thing that all relevant DMA backends can opt into, and not specific to VT-d. I mean, it's already more or less the same concept as the PowerPC secure VM thing.
Robin.
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