On 03/26/2012 01:30 PM, Michael S. Tsirkin wrote: > > > > > > > > > > > > + run->exit_reason = KVM_EXIT_MMIO; > > > > > + run->mmio.phys_addr = gpa; > > > > > + memcpy(run->mmio.data, &a0, 2); > > > > > + run->mmio.len = 2; > > > > > + run->mmio.is_write = 1; > > > > > + r = 0; > > > > > + } > > > > > + goto noret; > > > > > > > > What if the address is in RAM? > > > > Note the guest can't tell if a piece of memory is direct mapped or > > > > implemented as mmio. > > > > > > True but doing hypercalls for memory which can be > > > mapped directly is bad for performance - it's > > > the reverse of what we are trying to do here. > > > > It's bad, but the guest can't tell. > > > > Suppose someone implements virtio in hardware and we pass it through to > > a guest. It should continue working, no? > > Why would we want hypercalls then? > > As I see it, virtio device would have a capability > that tells the guest to use hypercalls for access. > An actual PCI device won't expose this capability, > as would a device on a host which lacks the hypercall. Ok, makes sense. > > > The intent is to use this for virtio where we can explicitly let the > > > guest know whether using a hypercall is safe. > > > > > > Acceptable? What do you suggest? > > > > It's iffy. > > Question is, do we want a bunch of dead code sitting there > just in case? And what are the chances it'll work correctly > when we need it to? If we make it device specific, I guess not. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
