On Thu, Mar 21, 2013 at 07:45:57AM -0700, H. Peter Anvin wrote: > On 03/21/2013 07:43 AM, Michael S. Tsirkin wrote: > >> > >> The reason to support this is that a guest written to only handle one or > >> the other doesn't prevent the hypervisor from offering the other to > >> guests. We probably want to specify that if the guest doesn't care, it > >> should use the first one offered by the host. > >> > > > > What are the configurations where having many ways is helpful? > > Any examples? > > > > In BIOS (e.g. SeaBIOS), using MMIO is very difficult, so your boot ROM > probably wants to use I/O space even if MMIO is available. Is this a real concern? Modern cards seem to supply PXE ROMs even though they have no IO BARs. > If you are preferring I/O space because it is faster (vmexit), then you > still want to allow MMIO if the resource is not available. > > -hpa Problem is, BIOS and OS normally assume failure to allocate any resources means card won't function and disable it. So it does not seem to be worth it to have such a device specific failover ability. > -- > H. Peter Anvin, Intel Open Source Technology Center > I work for Intel. I don't speak on their behalf. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
