On Wed, Feb 23, 2022 at 09:34:43AM -0700, Alex Williamson wrote: > On Tue, 22 Feb 2022 20:52:51 -0400 > Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > > > On Mon, Feb 21, 2022 at 11:40:42AM +0000, Shameer Kolothum wrote: > > > > > + /* > > > + * ACC VF dev BAR2 region consists of both functional register space > > > + * and migration control register space. For migration to work, we > > > + * need access to both. Hence, we map the entire BAR2 region here. > > > + * But from a security point of view, we restrict access to the > > > + * migration control space from Guest(Please see mmap/ioctl/read/write > > > + * override functions). > > > + * > > > + * Also the HiSilicon ACC VF devices supported by this driver on > > > + * HiSilicon hardware platforms are integrated end point devices > > > + * and has no capability to perform PCIe P2P. > > > > If that is the case why not implement the RUNNING_P2P as well as a > > NOP? > > > > Alex expressed concerned about proliferation of non-P2P devices as it > > complicates qemu to support mixes > > I read the above as more of a statement about isolation, ie. grouping. > Given that all DMA from the device is translated by the IOMMU, how is > it possible that a device can entirely lack p2p support, or even know > that the target address post-translation is to a peer device rather > than system memory. If this is the case, it sounds like a restriction > of the SMMU not supporting translations that reflect back to the I/O > bus rather than a feature of the device itself. Thanks, This is an interesting point.. Arguably if P2P addresses are invalid in an IOPTE then pci_p2pdma_distance() should fail and we shouldn't have installed them into the iommu in the first place. Jason
