Re: [Xen-devel] unhandled word causes Xen crash with recent Linux kernels, was: Re: [PATCH v2 05/11] xen/arm: vgic: Properly emulate the full register

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Ian,

On 25/11/15 12:26, Ian Campbell wrote:
> On Wed, 2015-11-25 at 12:15 +0000, Stefano Stabellini wrote:
>> On Wed, 25 Nov 2015, Shannon Zhao wrote:
>>> Upstream Linux kernel applies below patch which will write
>>> GICD_ICACTIVER. But since Xen doesn't support it, so it will cause Dom0
>>> initializes GIC failed.
>>>
>>> 0eece2b22849c90b730815c893425a36b9d10fd5 (irqchip/gic: Make sure all
>>> interrupts are deactivated at boot)
>>>
>>> (XEN) d0v0: vGICD: unhandled word write 0xffffffff to ICACTIVER4
>>> (XEN) traps.c:2447:d0v0 HSR=0x93860046 pc=0xffffffc0008d63f0
>>> gva=0xffffff8000004384 gpa=0x0000002f000384
>>> (XEN) DOM0: Unhandled fault: ttbr address size fault (0x96000000) at
>>> 0xffffff8000004384
>>> (XEN) DOM0: Internal error: : 96000000 [#1] PREEMPT SMP
>>> (XEN) DOM0: Modules linked in:
>>> (XEN) DOM0: CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.0-rc2+ #364
>>> (XEN) DOM0: Hardware name: (null) (DT)
>>> (XEN) DOM0: task: ffffffc000969970 ti: ffffffc00095c000 task.ti:
>>> ffffffc00095c000
>>> (XEN) DOM0: PC is at gic_dist_config+0x78/0xa0
>>> (XEN) DOM0: LR is at __gic_init_bases+0x240/0x2bc
>>>
>>> Do we have a plan to fix this?
>>
>> Thanks for the reporting the issue, I can reproduce the problem.  Given
>> that this is a very serious regression and that we cannot really "fix"
>> the Linux side because Linux is not doing anything wrong, I think we
>> have to go with a very simple change, something we can easily backport
>> to all past Xen releases.
>>
>> I suggest we turn the "unhandled word write" into a write_ignore, see
>> below:
> 
> As discussed IRL this might be tolerable as a patch intended for
> backporting purposes, but I would want to see it in a series along with one
> or more not-for-backport patches which actually makes the register work as
> it should.

I have the feeling that fixing properly GICD_I*ACTIVER will take
sometimes as we also need to take into consideration hardware interrupt
routed to a guest.

As this is preventing Linux upstream to run on the latest, can we get a
simple fix for now?

Regards,

-- 
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel