linux-kernel - [PATCH] x86/PCI: Don't alloc pcibios-irq when MSI is enabled

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Message-Id: <1444386214-26319-1-git-send-email-joro@8bytes.org>
Date:	Fri,  9 Oct 2015 12:23:34 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	x86@...nel.org, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, Joerg Roedel <jroedel@...e.de>,
	Jiang Liu <jiang.liu@...ux.intel.com>
Subject: [PATCH] x86/PCI: Don't alloc pcibios-irq when MSI is enabled

From: Joerg Roedel <jroedel@...e.de>

The pcibios-irq and MSI both use dev->irq to store the IRQ
number. While the MSI code checks for that and frees the
pcibios-irq before overwriting dev->irq, the
pcibios_alloc_irq function does not.

Usually this is not a problem, as the pcibios-irq is
allocated before probe time of the device and the MSI irq is
allocted from the drivers probe path.

But there are PCI devices handled by the core kernel and not
by a standard pci driver, like the AMD IOMMU for example.
For the AMD IOMMU a normal pci device driver does not make
sense, because a driver can be forcibly unbound from its
device, which is not a good idea for an IOMMU.

Nevertheless the PCI core code tries to match the PCI device
implementing the AMD IOMMU against drivers, and
allocates/frees a pcibios IRQ every time it tries out a new
driver. This overwrites the dev->irq field set by
pci_enable_msi() and sets it to 0 in the end (because the
probe fails and the pcibios-irq is freed again).

On suspend/resume this breaks the kernel, because the irq
descriptor for irq 0 is NULL.

Fix this by not allocating a pcibios-irq when MSI is
already active. This also has the benefit, that a device
claimed by the core kernel can not be probed by a pci driver
later.

Cc: Jiang Liu <jiang.liu@...ux.intel.com>
Reported-by: Borislav Petkov <bp@...en8.de>
Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/pci/common.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
index dc78a4a..6254c06 100644
--- a/arch/x86/pci/common.c
+++ b/arch/x86/pci/common.c
@@ -675,6 +675,14 @@ int pcibios_add_device(struct pci_dev *dev)

 int pcibios_alloc_irq(struct pci_dev *dev)
 {
+	/*
+	 * If the PCI device was already claimed by core code and has
+	 * MSI enabled, probing of the pcibios irq will overwrite
+	 * dev->irq.  So bail out if MSI is already enabled.
+	 */
+	if (pci_dev_msi_enabled(dev))
+		return -EBUSY;
+
 	return pcibios_enable_irq(dev);
 }

-- 
1.9.1

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