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Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions


From: Paul Brook
Subject: Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions
Date: Wed, 10 Jun 2009 15:07:34 +0100
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> > > Note that platform must set a flag to declare MSI supported.
> > > For PC this will be set by APIC.
> >
> > This sounds wrong. The device shouldn't know or care whether the system
> > has a MSI capable interrupt controller. That's for the guest OS to figure
> > out.
>
> You are right of course. In theory there's nothing that breaks if I
> set this flag to on, on all platforms. OTOH if qemu emulates some
> controller incorrectly, guest might misdetect MSI support in the
> controller, and things will break horribly.
>
> It seems safer to have a flag that can be enabled by people
> that know about a specific platform.

No. The solution is to fix whatever is broken.

If we really need to avoid MSI-X capable devices then that should be done 
explicity per-device. i.e. you have a different virtio-net device that does 
not use MSI-X.

Paul




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