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.2.02.1411251205220.2675@kaball.uk.xensource.com>
Date:	Tue, 25 Nov 2014 12:06:35 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
CC:	<david.vrabel@...rix.com>, <konrad.wilk@...cle.com>,
	<stefano.stabellini@...citrix.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 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?


> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> ---
>  arch/x86/pci/xen.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c
> index 093f5f4..1370716 100644
> --- a/arch/x86/pci/xen.c
> +++ b/arch/x86/pci/xen.c
> @@ -431,6 +431,14 @@ int __init pci_xen_init(void)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_PCI_MSI
> +void __init xen_msi_init(void)
> +{
> +	x86_msi.setup_msi_irqs = xen_hvm_setup_msi_irqs;
> +	x86_msi.teardown_msi_irq = xen_teardown_msi_irq;
> +}
> +#endif
> +
>  int __init pci_xen_hvm_init(void)
>  {
>  	if (!xen_have_vector_callback || !xen_feature(XENFEAT_hvm_pirqs))
> @@ -445,8 +453,11 @@ int __init pci_xen_hvm_init(void)
>  #endif
>  
>  #ifdef CONFIG_PCI_MSI
> -	x86_msi.setup_msi_irqs = xen_hvm_setup_msi_irqs;
> -	x86_msi.teardown_msi_irq = xen_teardown_msi_irq;
> +	/*
> +	 * We need to wait until after x2apic is initialized
> +	 * before we can set MSI IRQ ops.
> +	 */
> +	x86_platform.apic_post_init = xen_msi_init;
>  #endif
>  	return 0;
>  }
> -- 
> 1.9.3
> 
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