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Re: [Xen-devel] Re: [vt-d][xen4-rc6] Hangs on startup

To: "Nadolski, Ed" <Ed.Nadolski@xxxxxxx>
Subject: Re: [Xen-devel] Re: [vt-d][xen4-rc6] Hangs on startup
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Mon, 22 Mar 2010 18:05:43 -0400
Cc: Łukasz Oleś <lukaszoles@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On Mon, Mar 22, 2010 at 04:11:34PM -0600, Nadolski, Ed wrote:
> > -----Original Message-----
> > From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx]
> > Sent: Monday, March 22, 2010 2:54 PM
> > To: Nadolski, Ed
> > Cc: Łukasz Oleś; xen-devel@xxxxxxxxxxxxxxxxxxx
> > Subject: Re: [Xen-devel] Re: [vt-d][xen4-rc6] Hangs on startup
> > 
> > On Mon, Mar 22, 2010 at 03:06:48PM -0600, Nadolski, Ed wrote:
> > >
> > >
> > > > -----Original Message-----
> > >
> > > > PCI back is to be used _only_ with PV guests - you on the other
> > > > hand are running an HVM guest.
> > > >
> > > > Per the earlier statement, I would recommend you use the 'pciback'
> > > > instead of 'pci-stub' or just not compile pciback in and see what
> > > > happens. Keep in mind: PCI back module is only needed when you want
> > to
> > > > do PV PCI passthrough, which is not what you are doing.
> > >
> > > I'm confused - does that mean pci-stub must be used for device
> > assignment to an HVM guest?  The VTdHowTo isn't clear on that.
> > 
> > Not per say.
> > 
> > xen-pciback can be used for both PV and HVM.
> OK then what is the difference between pciback and xen-pciback?  I thought 
> they were just a re-name, but there must be more than that if one supports 
> HVM and the other doesn't.

That is is. Just a rename.
> > pci-stub can only be used for HVM guests.
> OK, but then why would I ever want to use pci-stub, if xen-pciback already 
> does both?

Uhh.. you probably wouldn't. But the pci-stub code has been in existence
in the Linux kernel for some time..
> > But there seems to be a bug somewhere that when the PCI device is
> > assigned to pci-stub, pciback tries to seize it and can't find it and
> > somehow is stuck in a spin-lock.  That shouldn't be happening.
> > 
> > Right now I am trying to figure out if we remove from Lukasza system
> > pciback and only use pci-stub whether he still gets those MFN lookup
> > errors with his QLogic card. Those are, I believe, a seperate issue
> > from the pciback spinlock failure.
> Yes, those sound like two different things.
> I too am seeing problems with a Qlogic card in an HVM.  It looks like my 
> card's BIOS makes an INT1A call (FIND PCI DEVICE function) that fails when 
> the HVM is booting, and the code hangs forever.

I would think this would work as the Bochs BIOS is actually being used
with real hardware. Is it possible that some data-structure that Bochs
BIOS has for the PCI enumeration is not up-to-date with the hvmloader
sets up? 

What about the BDF numbers? Any chance of trying to make them 1-to-1 (so
what you see in Dom0 is what you would see in DomU)?

Maybe there is an option in QEMU to do that?

What about passing in the PCI device _after_ the OS has booted. You can
do that by using 'pci-attach' (or something) flags. That will mean no
BIOS initialization, but the qla2xxx driver might be OK with that.

> But AFAICT it looks like Lukasz's latest trace hasn't gotten to the point 
> where it tries to load the PCI option ROM from the card.  I would be 
> interested to see if his card sees that error or not, once the MFN is 
> resolved.

> Has anyone used these Qlogic cards successfully under VT-d in a Xen HVM?  I 
> don't know of any reason why they should not work.  I'm assuming (hoping) 
> that they are virtualization-friendly enough to work under VT-d.

I think you and Lukasz are the first ones.

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