On Wed, Jun 05, 2013 at 07:41:17PM -0500, Anthony Liguori wrote: > "H. Peter Anvin" <hpa@xxxxxxxxx> writes: > > > On 06/05/2013 03:08 PM, Anthony Liguori wrote: > >>> > >>> Definitely an option. However, we want to be able to boot from native > >>> devices, too, so having an I/O BAR (which would not be used by the OS > >>> driver) should still at the very least be an option. > >> > >> What makes it so difficult to work with an MMIO bar for PCI-e? > >> > >> With legacy PCI, tracking allocation of MMIO vs. PIO is pretty straight > >> forward. Is there something special about PCI-e here? > >> > > > > It's not tracking allocation. It is that accessing memory above 1 MiB > > is incredibly painful in the BIOS environment, which basically means > > MMIO is inaccessible. > > Oh, you mean in real mode. > > SeaBIOS runs the virtio code in 32-bit mode with a flat memory layout. > There are loads of ASSERT32FLAT()s in the code to make sure of this. > Well, not exactly. Initialization is done in 32bit, but disk reads/writes are done in 16bit mode since it should work from int13 interrupt handler. The only way I know to access MMIO bars from 16 bit is to use SMM which we do not have in KVM. -- Gleb. -- 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
