Coalesced MMIO

[Sasha Levin <levinsasha928@gmail.com>]

Hello,

I've tried using KVM_REGISTER_COALESCED_MMIO to register a coalesced
MMIO zone.

ioctl(KVM_CHECK_EXTENSION) for KVM_CAP_COALESCED_MMIO works properly
(and returns 2).

ioctl(KVM_REGISTER_COALESCED_MMIO) with the zone also works fine (and
returns 0).

What I see is that we still get KVM_EXIT_MMIO into that zone, and the
ring never gets used (first==last==0 at all times).

I've went ahead and added some debug output to QEMU, I've noticed that
while qemu registers a coalesced MMIO zone for it's VGA driver,
kvm_flush_coalesced_mmio_buffer() never has any data to flush in the
ring either.

Is it a known issue? Or am I simply not doing something right?

Thanks!

-- 

Sasha.