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Re: [Xen-devel] [Xen-users] XEN/arm XENFB support

On Tue, 2013-12-17 at 08:20 +0100, peter wrote:

Please can you avoid top posting on the -devel list.

I've put -users and Lars to bcc since I think we are now well into
-devel territory.

> Thank you for the info/patch Ian.
> With some modifications to Qemu, I managed to cross compile
> qemu-system-arm with XEN support.
> Based on version: 1c514a7734b7f98625a0d18d5e8ee7581f26e50c (Merge remote
> branch 'perard/cpu-hotplug-port-v2' into xen-staging-master-7).
> And got my Qemu backend working.
> I can see that INPUT_XEN_KBDDEV_FRONTEND is working
> (d9) 6input: Xen Virtual Keyboard as /devices/virtual/input/input0
> (d9) 6input: Xen Virtual Pointer as /devices/virtual/input/input1
> And that XEN bus is prompting for VFB
> (d9) 6xenbus_probe_frontend: Device with no driver: device/vfb/0
> But it seems that the xen-fbfront only supports PV and not PVH. (Linux
> kernel 3.12-RC5)
> Because the init code is returning on:
>       if (!xen_pv_domain())
>               return -ENODEV;
> When I comment this code out.
> I do get these errors:
> [ 1698.899496] Failed to unmap pfn:5c081 rc:-2
> (XEN) dom10 IPA 0x0000000000000000
> (XEN) P2M @ 021b8300 mfn:0x4dc18
> (XEN) 1ST[0x0] = 0x000000004da276ff
> (XEN) 2ND[0x0] = 0x000000006b6856ff
> (XEN) 3RD[0x0] = 0x0000000000000000
> [ 1698.933034] Failed to map pfn to mfn rc:0:-22 pfn:5c349 mfn:0
> (XEN) dom10 IPA 0x000000002777c000
> (XEN) P2M @ 021b8300 mfn:0x4dc18
> (XEN) 1ST[0x0] = 0x000000004da276ff
> (XEN) 2ND[0x13b] = 0x0000000000000000
> [ 1698.951353] Failed to map pfn to mfn rc:0:-22 pfn:5c348 mfn:b6b2777c
> Yes lots of them, and my VFB is not working tough.
> So I've searched on the internet if someone got VFB on PVH working.
> But I couldn't find anything about, so is there someone who got VFB
> working on PVH (x86) ?

I've not heard of anyone, the focus of x86-PVH has been on getting the
basic functionality going.

In general PV drivers should just work but in some corner cases they
need adjustments for the "autotranslate" (i.e. hardware assisted paging)
case which is one of the key areas where both ARM, PVH-x86 and HVM-x86
differ from traditional PV-x86 guests.

So it might be that the vfb driver requires some such adjustment, or it
might be that the foreign mapping stuff is not working for you -- which
would be the same issue as you are having with domain building in the
other thread.

Given that I think we should try and get to the bottom of the foreign
mapping stuff first.

Eventually it might be worth investigating
 since the fb driver didn't really ought to be using foreign mappings anyway -- 
it should use grant references. However those patches only cover the frontend 
case and the author was using something other than qemu as the backend, so 
there is at least some actual development work required here.


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