On 05/18/2011 02:27 PM, Jan Kiszka wrote:
On 2011-05-18 21:10, Anthony Liguori wrote:
On 05/18/2011 10:30 AM, Jan Kiszka wrote:
You really don't need to register 90% of the time. In the case of a PC
with i440fx, it's really quite simple:
if an I/O is to the APIC page,
it's handled by the APIC
That's not that simple. We need to tell apart:
- if a cpu issued the request, and which one => forward to APIC
Right, but what I'm saying is that this logic lives in
kvm-all.c:kvm_run():case EXIT_MMIO.
Obviously for TCG, it's a bit more complicated but this should be
handled way before there's any kind of general dispatch.
- if the range was addressed by a device (PCI or other system bus
devices) => forward to MSI or other MMIO handlers
The same is true for MSI. Other MMIO handlers can be handled as
appropriate. For instance, once an I/O is sent to the PCI bus, you can
walk each PCI device's BAR list to figure out which device owns the I/O
event.
For ISA, it's a little trickier since ISA doesn't do positive decoding.
You need each ISA device to declare what I/O addresses it handles.
elif the I/O is in ROM regions:
if PAM RE or WE
redirect to RAM appropriately
else:
send to ROMs
elif the I/O is in the PCI windows:
send to the PCI bus
else:
send to the PIIX3
For x86, you could easily completely skip the explicit registration and
just have a direct dispatch to the i440fx and implement something
slightly more fancy than the above.
And I think this is true for most other types of boards too.
This all melts down that we need to stop accepting memory region
mappings from everywhere at core level, but properly dispatch them up
the device tree. A device should register against its bus which can then
forward or handle the mapping directly. And that handling requires a
central tool box to avoid reinventing wheels.
That's a worthwhile change, though a much bigger one than I was
originally hoping to get away with.
Agreed and as long as we've got the right long term vision in mind, we
don't have to do everything up front.
Regards,
Anthony Liguori
Jan
