On 07/02/2013 08:07:53 PM, Alexander Graf wrote: > > On 03.07.2013, at 01:25, Yoder Stuart-B08248 wrote: > > > 8. Open Issues > > > > -how to handle cases where VFIO is requested to handle > > a device where the valid, mappable range for a region > > is less than a page size. See example above where an > > advertised region in the DMA node is 4 bytes. If exposed > > to a guest VM, the guest has to be able to map a full page > > of I/O space which opens a potential security issue. > > The way we solved this for legacy PCI device assignment was by going > through QEMU for emulation and falling back to legacy read/write > IIRC. We could probably do the same here. IIRC there was a way for a > normal Linux mmap'ed device region to trap individual accesses too, > so we could just use that one too. > > The slow path emulation would then happen magically in QEMU, since > MMIO writes will get reinjected into the normal QEMU MMIO handling > path which will just issue a read/write on the mmap'ed region if it's > not declared as emulated. I agree that's what should happen by default, but there should be a way for root to tell vfio that a device is allowed to overmap, in order to get the performance benefit of direct access in cases where root knows (or explicitly doesn't care) that it is safe. -Scott _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm
