Re: [Qemu-ppc] [Qemu-devel] [PATCH] RFC kvm irqfd: add directly mapped MSI IRQ support

[Anthony Liguori]

On Sun, Jun 23, 2013 at 4:39 PM, Benjamin Herrenschmidt
<address@hidden> wrote:
> On Sun, 2013-06-23 at 10:02 -0500, Anthony Liguori wrote:
>> It doesn't make a lot of sense to have Power do MSI decoding in
>> userspace while x86 does it in the kernel.  I assume the kernel
>> doesn't have enough information to do the translation on Power?
>
> Well, it would need the host bridge which it doesn't have and it
> would need a concept of mapping that to interrupt numbers which
> we don't want in the kernel.
>
> We can keep the kernel side a LOT simpler (completely avoiding
> the whole route bloatware) by sticking to our "simple" direct map kernel
> stuff and doing the mapping from address/data to interrupts in qemu, so
> we'll stick to that.

Yeah, but none of this is Power specific...  so we can do the same for x86, no?

I'm still trying to wrap my head around why we need MSI knowledge at
all in the kernel for x86.  I presume it's to fast-path irqfd when
doing vhost?

Regards,

Anthony Liguori

>
> Cheers,
> Ben.
>
>