linux-kernel - Re: [PATCH] PCI/MSI: Fix MSI IRQ domains for SR-IOV

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Message-ID: <20150920125848.37d04b21@arm.com>
Date:	Sun, 20 Sep 2015 12:58:48 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	<linux-pci@...r.kernel.org>, <bhelgaas@...gle.com>,
	<tglx@...utronix.de>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI/MSI: Fix MSI IRQ domains for SR-IOV

On Fri, 18 Sep 2015 15:08:54 -0600
Alex Williamson <alex.williamson@...hat.com> wrote:

Hi Alex,

> SR-IOV creates a virtual bus where bus->self is NULL.  This results
> in a segfault as VFs are added and we scan for an MSI domain without
> taking that into account.  Detect this and scan up to the parent bus
> until we find a real bridge.

Irk. Sorry about the breakage.

> Fixes: 44aa0c657e3e ("PCI/MSI: Add hooks to populate the msi_domain field")
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> ---
>  drivers/pci/probe.c |   17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 0b2be17..b42419e 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -676,15 +676,20 @@ static struct irq_domain *pci_host_bridge_msi_domain(struct pci_bus *bus)
>  static void pci_set_bus_msi_domain(struct pci_bus *bus)
>  {
>  	struct irq_domain *d;
> +	struct pci_bus *b;
>  
>  	/*
> -	 * Either bus is the root, and we must obtain it from the
> -	 * firmware, or we inherit it from the bridge device.
> +	 * The bus can be a root bus, a subordinate bus, or a virtual bus
> +	 * created by an SR-IOV device.  Walk up to the first bridge device
> +	 * found or derive the domain from the host bridge.
>  	 */
> -	if (pci_is_root_bus(bus))
> -		d = pci_host_bridge_msi_domain(bus);
> -	else
> -		d = dev_get_msi_domain(&bus->self->dev);
> +	for (b = bus, d = NULL; !d && !pci_is_root_bus(b); b = b->parent) {
> +		if (b->self)
> +			d = dev_get_msi_domain(&b->self->dev);
> +	}
> +
> +	if (!d)
> +		d = pci_host_bridge_msi_domain(b);
>  
>  	dev_set_msi_domain(&bus->dev, d);
>  }
> 

Out of curiosity, is this a common behaviour? I've tested the original
code with an Intel i350 Ethernet interface (IGB+IGBVF), and used it
with virtual functions on my arm64-based Seattle, without any issue. Do
we have divergent implementations of the same functionality in the
kernel? Otherwise:

Acked-by: Marc Zyngier <marc.zyngier@....com>

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny.
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