Re: [Xen-devel] [PATCH v3 1/2] xen/pci: Defer initialization of MSI ops on HVM guests until after x2APIC has been set up

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 11/25/2014 07:06 AM, Stefano Stabellini wrote:
> On Mon, 24 Nov 2014, Boris Ostrovsky wrote:
> > If the hardware supports APIC virtualization we may decide not to use pirqs
> > and instead use APIC/x2APIC directly, meaning that we don't want to set
> > x86_msi.setup_msi_irqs and x86_msi.teardown_msi_irq to Xen-specific routines.
> > However, x2APIC is not set up by the time pci_xen_hvm_init() is called so we
> > need to postpone setting these ops until later, when we know which APIC mode
> > is used.
> >
> > (Note that currently x2APIC is never initialized on HVM guests. This may
> > change in the future)
> I take that this is safe because no MSIs can be received at this point
> (apic_post_init), right?

Yes. At the time apic_post_init() is called PCI has not been probed yet.

-boris



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