Re: [Xen-devel] PCI passthrough will cause unknown device appearance in device manager of Windows OS via xenstore keys

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Apr 10, 2017 at 01:46:20PM +0100, Andrew Cooper wrote:
> On 10/04/17 12:24, lidonglin wrote:
> >
> > Hi all:
> >
> >                 I have one question about PCI passthrough. I found
> > that if I created a VM with host pci device(cfg file as below), there
> > were some xenstore keys exsiting in /local/domain/0 and
> > /local/domain/DomID/. Besides I found one unknown device in device
> > manager of Windows OS with Class ID FF80 from vendor ID 5853. My
> > questions  are as below:
> >
> >  
> >
> > 1.       Why do we create frontend and backend key pairs in xenstore?
> >  I think  Passthrough is not PV,  was it possible that we just used
> > these keys to record something?
> >
> > 2.        After review the code, I think backend keys are used to
> > record state of hostdev, some codes will query something using these
> > keys. But for frontend keys, can we delete them?
> >
> > 3.       if frontend keys exist in xenstore, then unknown device will
> > appear in device manager. Can we fix this?  For  an obsessive,  he
> > can’t stand for this.
> >
> 
> This is a libxl bug which has been reported before, but nothing happened.
> 
> libxl must not start a PV pci-back when doing HVM PCI passthrough using
> qemu, because absolutely nothing good can come of having two different
> ways of poking at PCI state.
> 
> The patch, unchanged from before, is
> https://github.com/xenserver/xen-4.7.pg/blob/master/master/0001-libxl-Don-t-insert-PCI-device-into-xenstore-for-HVM-.patch
> 

ISTR Konrad made some comments about it. CC Konrad.

> ~Andrew

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