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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Date:	Tue, 25 Nov 2014 10:11:39 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	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 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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