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

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Message-ID: <alpine.DEB.2.02.1411251511580.2675@kaball.uk.xensource.com>
Date:	Tue, 25 Nov 2014 15:12:14 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	<david.vrabel@...rix.com>, <konrad.wilk@...cle.com>,
	<jun.nakajima@...el.com>, <linux-kernel@...r.kernel.org>,
	<xen-devel@...ts.xen.org>
Subject: Re: [PATCH v3 1/2] xen/pci: Defer initialization of MSI ops on HVM
 guests until after x2APIC has been set up

On Tue, 25 Nov 2014, Boris Ostrovsky wrote:
> 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.

Please add that to the commit message.

Acked-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
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