linux-kernel - Re: [PATCH] x86/PCI: Fully disable devices before releasing IRQ resource

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Date:	Fri, 06 Mar 2015 09:49:04 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Alex Williamson <alex.williamson@...hat.com>, x86@...nel.org,
	rjw@...ysocki.net, mingo@...hat.com, bp@...en8.de,
	lv.zheng@...el.com, hpa@...or.com, bhelgaas@...gle.com,
	tglx@...utronix.de, yinghai@...nel.org, lenb@...nel.org
CC:	linux-pci@...r.kernel.org, tony.luck@...el.com,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/PCI: Fully disable devices before releasing IRQ resource

On 2015/3/6 5:06, Alex Williamson wrote:
> The IRQ resource for a device is established when pci_enabled_device()
> is called on a fully disabled device (ie. enable_cnt == 0).  With
> commit b4b55cda5874 ("x86/PCI: Refine the way to release PCI IRQ
> resources") this same IRQ resource is released when the driver is
> unbound from the device, regardless of the enable_cnt.  This presents
> the situation that an ill-behaved driver can now make a device
> unusable to subsequent drivers by an imbalance in their use of
> pci_enable/disable_device().  It's one thing to break your own device
> if you're one of these ill-behaved drivers, but it's a serious
> regression for secondary drivers like vfio-pci, which are innocent
> of the transgressions of the previous driver.
> 
> Resolve by pushing the device to a fully disabled state before
> releasing the IRQ resource.
> 
> Fixes: b4b55cda5874 ("x86/PCI: Refine the way to release PCI IRQ resources")
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> Cc: Jiang Liu <jiang.liu@...ux.intel.com>
> ---
>  arch/x86/pci/common.c |   13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
> index 3d2612b..4810194 100644
> --- a/arch/x86/pci/common.c
> +++ b/arch/x86/pci/common.c
> @@ -527,8 +527,19 @@ static int pci_irq_notifier(struct notifier_block *nb, unsigned long action,
>  	if (action != BUS_NOTIFY_UNBOUND_DRIVER)
>  		return NOTIFY_DONE;
>  
> -	if (pcibios_disable_irq)
> +	if (pcibios_disable_irq) {
> +		/*
> +		 * Broken drivers may allow a device to be .remove()'d while
> +		 * still enabled.  pci_enable_device() will only re-establish
> +		 * dev->irq if the devices is fully disabled.  So if we want
> +		 * to release the IRQ, we need to make sure the next driver
> +		 * can re-establish it using pci_enable_device().
> +		 */
> +		while (pci_is_enabled(dev))
> +			pci_disable_device(dev);
> +
>  		pcibios_disable_irq(dev);
> +	}
Hi Alex,
	Thanks for debugging and fixing it.
	Will it be feasible to give a debug message to remind those
driver authors to correctly disable PCI when unbinding?
Regards!
Gerry

>  
>  	return NOTIFY_OK;
>  }
> 
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