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Re: [Qemu-devel] [Qemu-ppc] [PATCH] RFC kvm irqfd: add directly mapped M

From: Gleb Natapov
Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH] RFC kvm irqfd: add directly mapped MSI IRQ support
Date: Mon, 24 Jun 2013 15:39:43 +0300

On Mon, Jun 24, 2013 at 07:24:03AM -0500, Anthony Liguori wrote:
> Alex Williamson <address@hidden> writes:
> > On Sun, 2013-06-23 at 16:58 -0500, Anthony Liguori wrote:
> >> 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?
> >
> > Or device assignment.  Any paths where we want to inject an MSI
> > interrupt without going through userspace.  Thanks,
> With VFIO, we use irqfd, if we program the irqfd as the underlying IRQ
> that MSI would route to, isn't that sufficient?
Not sure I understand what you mean by IRQ here, there is no "IRQ pin"
on x86 CPU with APIC architecture (there is ExtINT but it is not
relevant here). If by IRQ you mean "information needed to inject
interrupt through APIC" then this is how things work now.

> That's more or less what Ben is proposing for Power...
> Regards,
> Anthony Liguori
> >
> > Alex


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