linux-kernel - Re: [Patch v4 21/23] x86/PCI: Refine the way to release PCI IRQ resources

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Date:	Wed, 04 Mar 2015 16:48:43 -0700
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Borislav Petkov <bp@...en8.de>, Lv Zheng <lv.zheng@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Len Brown <lenb@...nel.org>, Tony Luck <tony.luck@...el.com>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-acpi@...r.kernel.org
Subject: Re: [Patch v4 21/23] x86/PCI: Refine the way to release PCI IRQ
 resources

On Wed, 2015-03-04 at 09:06 -0700, Alex Williamson wrote:
> Hi,
> 
> I'm getting a regression from this patch when using VFIO for device
> assignment to a QEMU VM.  I have a device initially bound to the nouveau
> driver, which is unbound from that driver and bound to vfio-pci for use
> by userspace.  vfio-pci calls pci_enable_device, but when userspace
> attempts to setup the legacy INTx interrupt, pci_dev->irq is zero and
> vfio-pci errors with -ENODEV.
> 
> Where is pci_dev->irq supposed to be getting re-initialized in this
> case?  Am I missing an important initialization step in vfio-pci?  I
> certainly don't think I should be calling request_irq(pci_dev->irq, ...
> when pci_dev->irq is zero.  Thanks,

It looks like the imbalance is in pci_dev->enable_cnt.  Any call to
pci_disable_device() will clear pci_dev->irq, but pci_enable_device()
does effectively nothing unless it's called with enable_cnt == zero.  So
I'm at the mercy of the previous driver behaving relatively sanely in
order to re-enable legacy interrupts for a device :-\  Maybe the unbound
notifier needs to do some sanitizing of the device?  Thanks,

Alex

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