Re: [PATCH 1/7] KVM: api: add kvm_irq_routing_extended_msi

[Paolo Bonzini <pbonzini@redhat.com>]

On 06/07/2015 13:23, Andre Przywara wrote:
> Hi Paolo,
> 
> thanks for looking at this!
> 
> On 06/07/15 12:07, Paolo Bonzini wrote:
>>
>>
>> On 06/07/2015 12:37, Christoffer Dall wrote:
>>> I don't view it as 'the kernel requires this' but as 'the kernel will
>>> not complain with arbitrary error code if you set the devid flag'
>>> capability, and it's up to userspace (as usual) to provide the correct
>>> arguments for things to work, and up to the kernel to ensure we don't
>>> crash the system etc.
>>>
>>> Thus, if you want to advertise it as a capability, I would rather call
>>> it KVM_CAP_MSI_DEVID.
>>
>> I agree.  Does userspace know that ITS guests always require devid?
> 
> Well, as we are about to implement this: yes. But the issue is that MSI
> injection and GSI routing code is generic PCI code in userland (at least
> in kvmtool, guess in QEMU, too), so I don't want to pull in any kind of
> ARM specific code in there. The idea is to always provide the device ID
> from the PCI code (for PCI devices it's just the B/D/F triplet), but
> only send it to the kernel if needed. Querying a KVM capability is
> perfectly fine for this IMO.

Yes, I agree.

Paolo