Re: [Qemu-devel] [Xen-devel] [PATCH RESEND] fix MSI injection on Xen

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Jan 13, 2016 at 02:59:09PM +0000, Stefano Stabellini wrote:
> On Xen MSIs can be remapped into pirqs, which are a type of event
> channels. It's mostly for the benefit of PCI passthrough devices, to
> avoid the overhead of interacting with the emulated lapic.
> 
> However remapping interrupts and MSIs is also supported for emulated
> devices, such as the e1000 and virtio-net.
> 
> When an interrupt or an MSI is remapped into a pirq, masking and
> unmasking is done by masking and unmasking the event channel. The
> masking bit on the PCI config space or MSI-X table should be ignored,
> but it isn't at the moment.
> 
> As a consequence emulated devices which use MSI or MSI-X, such as
> virtio-net, don't work properly (the guest doesn't receive any
> notifications). The mechanism was working properly when xen_apic was

By xen_apic I presume the Linux Xen APIC code?

> introduced, but I haven't narrowed down which commit in particular is
> causing the regression.

It sounds like the issue was due to the Xen APIC code? Or am I misreading it?