linux-kernel - Re: 3.19-rc4: Xen pci-passthrough regression, bisected to commit cffe0a2b5a34c95a4dadc9ec7132690a5b0f6687 "x86, irq: Keep balance of IOAPIC pin reference count"

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Date:	Wed, 14 Jan 2015 14:58:33 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Sander Eikelenboom <linux@...elenboom.it>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>
Subject: Re: 3.19-rc4: Xen pci-passthrough regression, bisected to commit
 cffe0a2b5a34c95a4dadc9ec7132690a5b0f6687 "x86, irq: Keep balance of IOAPIC
 pin reference count"

On 14/01/15 14:15, Sander Eikelenboom wrote:
> Hi Gerry / David / Konrad,
> 
> Some more testing uncovered another issue under Xen, this time with PCI-passthrough.

What device?  In particular what interrupts is it using?

> I have bisected it to the following commit: 
> cffe0a2b5a34c95a4dadc9ec7132690a5b0f6687 "x86, irq: Keep balance of IOAPIC pin reference count"
> 
> It causes these symptoms:
> 
> - On Intel
>   - Running on Xen with pci devices seized on host boot with xen-pciback.hide= parameter
>   - Running a HVM guest with PCI passthrough of two devices (NIC + wireless NIC)
>   - While the driver loads fine, the device isn't working properly, looking in /proc/interrupts in the guest
>     shows that it doesn't receive any interrupts.
>   - Reverting this particular commit (in the dom0 kernel only) makes the device receive interrupts and work properly again.
> 
> - On AMD (more subtle symptom) 
>   - Running on Xen with pci devices seized on host boot with xen-pciback.hide= parameter
>   - Running a HVM guest with PCI passthrough of one devices (videograbber)
>   - While the driver loads fine and the device looks like it's working, the videostream isn't stable and it skips or repeats frames.
>   - Reverting this particular commit (in the dom0 kernel only) makes the device work properly again with a stable videostream.
> 
> --
> Sander
> 

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