[vfio-users] Interrupt Handling: Regression or config change?

[Alex Williamson]

On Thu, 5 Jan 2017 19:14:29 +0100
Ede Wolf <listac at nebelschwaden.de> wrote:

> Hello,
> 
> Running arch, I am having a windows XP guest, to which I am passing 
> through a PCIe Parallel Card, that again talks to a device that 
> unfortunately is very picky about interrupts and more so the interrupt 
> setting within Windows XP for that parallel port.
> 
> For a short explanation: Windows XP offers 3 ways to operate the 
> parallel port:
> "never use an interrupt"
> "try not to use an interrupt"
> "Use any interrupt assigned to that port"
> 
> My device requires the last option, otherwise communication does simply 
> not work, albeit the device itself is detected. So it seems, that 
> whatever setting I choose within windows xp, it is now ignored and does 
> not make any difference any more.
> 
> However, it used to work perfectly fine up to Kernel 4.5. or 4.6, I do 
> not remember exactly, but does not work any more with 4.8. Skipped 4.7 
> for sure.
> 
> Booting into the 4.4-lts kernel makes things work as expected, booting 
> into 4.8.x and communication is broken again. Can be repeated at will 
> with consistently the same results and holds true now for several 
> incarnations of the 4.8 kernel the archlinux team has provided so far.
> 
> Now I am wondering: Is there any compelling configuration change that I 
> am not aware of or is this simply a bug? And if, is this related to vfio 
> or other parts of the kernel and this the wrong place?
> 
> Thanks for any help

Any chance you could narrow down where this broke a little further,
perhaps even bisecting the kernel to a specific commit?  Thanks,

Alex