Re: [PATCH] KVM: Allow host IRQ sharing for assigned PCI 2.3 devices

[Jan Kiszka <jan.kiszka@web.de>]

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On 2012-01-10 21:44, Michael S. Tsirkin wrote:
> On Tue, Jan 10, 2012 at 08:40:59PM +0100, Jan Kiszka wrote:
>> On 2012-01-10 20:04, Michael S. Tsirkin wrote:
>>>>>  But IMO this
>>>>> shows it is a more generic interface.
>>>>
>>>> I'm worried about adding something new that will soon become obsolete
>>>> again. That's wasted effort IMHO unless we say today that there will be
>>>> no in-kernel MSI-X support.
>>>>
>>>> Jan
>>>
>>> Yes. But as we are adding a new interface maybe it's better to add a
>>> more generic one? I don't insist as I don't have a specific proposal,
>>> just something to consider.
>>
>> I could imagine defining an extensible IRQ masking interface, e.g. with
>> flags that select the type, but only implementing it for INTx for now.
>>
>> Jan
>>
> 
> I guess if we pass in the IRQ# the type can be inferred and does not
> need to be passed in.

What kind of number, a GSI? We do not yet track what is behind a GSI, do we?

Hmm, I think this requires more careful thoughts. What should be the
semantic of "mask" for the addressed device behind the IRQ? For assigned
legacy IRQ it's clear: mask at config space level. For assigned MSI-X it
should be masking at vector level. What about assigned MSI? What about
irqfds? How to deal with future IRQ sources?

No, I think it is better to directly associate the masking feature
directly with the source instead of doing this via some handle,
potentially addressing the whole world. If there is a need for
KVM_IRQFD_MASK, then let's introduce it. As a separate API.

Jan


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