On 02/28/2013 07:24 AM, Michael S. Tsirkin wrote:
>
> 3. hypervisor assigned IO address
> qemu can reserve IO addresses and assign to virtio devices.
> 2 bytes per device (for notification and ISR access) will be
> enough. So we can reserve 4K and this gets us 2000 devices.
> From KVM perspective, nothing changes.
> We'll want some capability in the device to let guest know
> this is what it should do, and pass the io address.
> One way to reserve the addresses is by using the bridge.
> Pros: no need for host kernel support
> Pros: regular PIO so fast
> Cons: does not help assigned devices, breaks nested virt
>
> Simply counting pros/cons, option 3 seems best. It's also the
> easiest to implement.
>
The problem here is the 4K I/O window for IO device BARs in bridges.
Why not simply add a (possibly proprietary) capability to the PCI bridge
to allow a much narrower window? That fits much more nicely into the
device resource assignment on the guest side, and could even be
implemented on a real hardware device -- we can offer it to the PCI-SIG
for standardization, even.
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
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