On Fri, Oct 6, 2017 at 3:45 PM, David Woodhouse <dwmw2@xxxxxxxxxxxxx> wrote: > On Fri, 2017-10-06 at 15:35 -0700, Dan Williams wrote: >> Add a helper to determine if the dma mappings set up for a given device >> are backed by an iommu. In particular, this lets code paths know that a >> dma_unmap operation will revoke access to memory if the device can not >> otherwise be quiesced. The need for this knowledge is driven by a need >> to make RDMA transfers to DAX mappings safe. If the DAX file's block map >> changes we need to be to reliably stop accesses to blocks that have been >> freed or re-assigned to a new file. > > "a dma_unmap operation revoke access to memory"... but it's OK that the > next *map* will give the same DMA address to someone else, right? I'm assuming the next map will be to other physical addresses and a different requester device since the memory is still registered exclusively.
