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

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Date:	Fri, 9 Oct 2015 11:26:08 +0100 (IST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Joerg Roedel <joro@...tes.org>
cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	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>,
	Jiang Liu <jiang.liu@...ux.intel.com>
Subject: Re: [PATCH] x86/PCI: Don't alloc pcibios-irq when MSI is enabled

On Fri, 9 Oct 2015, 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>

Reviewed-by: Thomas Gleixner <tglx@...utronix.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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