Re: [Xen-devel] [PATCH qemu-xen-traditional] xen/pt: allow QEMU to request MSI unmasking at bind time

[Ian Jackson <ian.jackson@xxxxxxxxxx>]

> >Ian, any objections?

Sorry for dropping this.  It's been a while!

> >> > When a MSI interrupt is bound to a guest using
> >> > xc_domain_update_msi_irq (XEN_DOMCTL_bind_pt_irq) the interrupt
> >> > is left masked by default.
> >> >
> >> > This causes problems with guests that first configure
> >> > interrupts and clean the per-entry MSIX table mask bit and
> >> > afterwards enable MSIX globally. In such scenario the Xen
> >> > internal msixtbl handlers would not detect the unmasking of
> >> > MSIX entries because vectors are not yet registered since MSIX
> >> > is not enabled, and vectors would be left masked.
> >> >
> >> > Introduce a new flag in the gflags field to signal Xen whether
> >> > a MSI interrupt should be unmasked after being bound.
> >> >
> >> > This also requires to track the mask register for MSI
> >> > interrupts, so QEMU can also notify to Xen whether the MSI
> >> > interrupt should be bound masked or unmasked

I searched my email archives but I haven't been able to find a copy of
the actual patch.  Was it ever sent to me ?

Also, qemu-trad is quite deeply frozen.  I'd like an explanation of
the practical impact of this bug, and the use cases where the fix is
needed, to justify the change.  Sorry to be awkward.

Regards,
Ian.

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