On Aug 27, 2014 4:30 AM, "Rusty Russell" <rusty@xxxxxxxxxxxxxxx> wrote: > > Andy Lutomirski <luto@xxxxxxxxxxxxxx> writes: > > Currently, a lot of the virtio code assumes that bus (i.e. hypervisor) > > addresses are the same as physical address. This is false on Xen, so > > virtio is completely broken. I wouldn't be surprised if it also > > becomes a problem the first time that someone sticks a physical > > "virtio" device on a 32-bit bus on an ARM SOC with more than 4G RAM. > > > > Would you accept patches to convert virtio_ring and virtio_pci to use > > the DMA APIs? I think that the only real catch will be that > > virtio_ring's approach to freeing indirect blocks is currently > > incompatible with the DMA API -- it assumes that knowing the bus > > address is enough to call kfree, and I don't think that the DMA API > > provides a reverse mapping like that. > > Hi Andy, > > This has long been a source of contention. virtio assumes that > the hypervisor can decode guest-physical addresses. > > PowerPC, in particular, doesn't want to pay the cost of IOMMU > manipulations, and all arguments presented so far for using an IOMMU for > a virtio device are weak. And changing to use DMA APIs would break them > anyway. > > Of course, it's Just A Matter of Code, so it's possible to > create a Xen-specific variant which uses the DMA APIs. I'm not sure > what that would look like in the virtio standard, however. I'll reply in the other thread to keep everything in one place. > > Cheers, > Rusty. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
