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Re: [Xen-devel] pci-passthrough loses msi-x interrupts ability after domain destroy

On Wed, Sep 20, 2017 at 03:50:35PM -0400, Jérôme Oufella wrote:
> Hi Xen-devel, 
> I'm using PCI pass-through to map a PCIe (intel i210) controller into 
> a HVM domain. The system uses xen-pciback to hide the appropriate PCI 
> device from Dom0. 
> When creating the HVM domain after an hypervisor cold boot, the HVM 
> domain can access and use the PCIe controller without problem. 
> However, if the HVM domain is destroyed then restarted, it won't be 
> able to use the pass-through PCI device anymore. The PCI device is 
> seen and can be mapped, however, the interrupts will not be passed to 
> the HVM domain anymore (this is visible under a Linux guest as 
> /proc/interrupts counters remain 0). The behavior on a Windows10 guest 
> is the same. 
> A few interesting hints I noticed: 
> - On Dom0, 'lspci -vv' on that PCIe device between the "working" and 
> the "muted interrupts" states, I noted a difference between the 
> MSI-X caps: 
> - Capabilities: [70] MSI-X: Enable- Count=5 Masked- <-- IRQs will work if 
> domain started 
> + Capabilities: [70] MSI-X: Enable- Count=5 Masked+ <-- IRQs won't work if 
> domain started
>                                             ^^^^^^^

IMHO it seems that either your device is not able to perform a reset
successfully, or Linux is not correctly performing such reset. I don't
think there's a lot that can be done from the Xen side.

Thanks, Roger.

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