Re: [Xen-devel] [BUG] Xen vm kernel crash in get_free_entries.

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

Saturday, October 19, 2013, 1:03:17 PM, you wrote:

> On Sat, 2013-10-19 at 14:51 +0400, Astarta wrote:
>> On 10/19/2013 03:14 AM, Sander Eikelenboom wrote:

>> > makes a HVM guest (qemu-xen-traditional) with xen_platform_pci=0 boot 
>> > again using xl, haven't tested it with xend.
>> >
>> Great catch!
>> I also confirm that 3.11.5 kernel boots just fine after reverting of 
>> 'correctly initialize grant table version 1' patch.

> This could just be down to that patch adding some BUG_ONs to catch bad
> things going on, e.g. the one in gnttab_expand which I think is being
> hit here.

> I have a feeling that it is still wrong (but just more benign) to be
> hitting that call chain in a configuration where there is no platform
> device driver running. IOW reverting that patch removes the obvious
> symptom (blowing up) but not the root cause, i.e. the patch is doing its
> job.

That was my suspicion too, but at least it seems like some starting point
of further debugging.
(and indication of the kernels affected since this commit went to stable as 
well)

Since i was still seeing the "Booting PV enabled guest on Xen HVM" is was 
wondering
what is supposed to happen when there are some combinations ....

xen HVM xen_platform_pci=0 + guest kernel without PV guest support and without 
xen pv drivers (net + block)

xen HVM xen_platform_pci=0 + guest kernel with PV guest support but without xen 
pv drivers (net + block)

xen HVM xen_platform_pci=0 + guest kernel with PV guest support and with xen pv 
drivers (net + block)
-- This is the configuration that hits the bug described here.

xen HVM xen_platform_pci=1 + guest kernel without PV guest support and without 
xen pv drivers (net + block)

xen HVM xen_platform_pci=1 + guest kernel with PV guest support and without xen 
pv drivers (net + block)

xen HVM xen_platform_pci=1 + guest kernel with PV guest support and with xen pv 
drivers (net + block)


Booting a guest kernel with PV support as HVM but without using PV doesn't seem 
possible with a .cfg option ?
(yes it's a hypothetical option (performance wise), as is running with a guest 
kernel which supports PV drivers,
 but not using them with xen_platform_pci=0 .. but it is useful for debugging )

--
Sander

> Ian.




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