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

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Date:	Fri, 23 Oct 2015 10:02:11 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Bjorn Helgaas <helgaas@...nel.org>, Joerg Roedel <joro@...tes.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH] x86/PCI: Don't alloc pcibios-irq when MSI is enabled

On 2015/10/22 0:23, Bjorn Helgaas wrote:
> On Fri, Oct 09, 2015 at 12:23:34PM +0200, Joerg Roedel wrote:
>> 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>
> 
> Applied with Thomas' reviewed-by to pci/msi for v4.4, thanks, Joerg!
Hi Bjorn,
	There's another patch already merged into mainstream kernel,
which solves this issue in another way by making use of
pci_dev->match_driver flag. Please refer to:
cbbc00be2ce3 ("iommu/amd: Prevent binding other PCI drivers to IOMMU PCI
devices")
	So I think this patch is redundant now.
Thanks,
Gerry

> 
>> ---
>>  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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