Re: [Qemu-devel] [PATCH] MSI / MSIX injection for Xen HVM

[Jan Kiszka]

On 2012-04-03 18:44, Wei Liu wrote:
> On Thu, 2012-03-01 at 15:56 +0000, Paolo Bonzini wrote:
>> Il 01/03/2012 15:50, Stefano Stabellini ha scritto:
>>>>>>> That is a good point actually: we already have lapic emulation in Xen,
>>>>>>> it makes sense to have apic-msi in Xen too.
>>>>>>> We would still need the changes to msi_notify and msix_notify though.
>>>>>
>>>>> Why?  The stores would just go to the Xen interrupt controller MMIO area
>>>>> which then does the xc_hvm_inject_msi.
>>>  
>>> Because msi(x)_notify is called by QEMU's emulated devices: it is not
>>> possible from QEMU to cause an emulation trap in Xen on behalf of the
>>> guest.
>>
> 
> I'm not a QEMU expert, so following question may be dumb. However I do
> care about a cleaner implementation. So please be patient with me. :-)
> 
>> msi{x,}_notify doesn't have to go to Xen MMIO emulation, so in Wei's
>> patch you don't need anymore the msi{,x}_notify parts, only apic_send_msi.
>>
> 
> I don't quite understand "you don't need anymore the msi{,x}_notify
> parts". Virtio PCI invokes msi_notify directly. If I don't hook up
> msi{,x}_notify, how can I deal with devices like Virtio PCI?

See how KVM will solve this in [1].

Jan

[1] http://permalink.gmane.org/gmane.comp.emulators.kvm.devel/89121

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