Re: [Xen-users] Got permission denied error when calling xenbus_printf function in the frontend driver

[Jintack Lim <jintack@xxxxxxxxxxxxxxx>]

On Sat, Aug 8, 2015 at 12:57 AM, Jintack Lim <jintack@xxxxxxxxxxxxxxx> wrote:
> On Tue, Aug 4, 2015 at 7:15 AM, Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:
>> On Tue, 2015-08-04 at 07:07 -0400, Jintack Lim wrote:
>>> After I added a few lines to give read/write permission of some keys to
>>> domU,
>>> then "permission denied" error was gone, and the driver worked fine.
>>
>> Great!
>
> Thanks!
>
> I got one more question.
> I wonder if the backend/frontend driver on PV are supposed to work
> well on HVM as well.
>
> My backend/frontend driver worked well on ARM64 PV domains.
> However, when I ran the same driver on x86 PV driver domain and HVM
> guest domain(PVHVM),
> I got a kernel panic in the backend driver as soon as I fired the
> probe function in the backend.
> More specifically, it's when the backend driver tries to send a
> notification through
> evtchn_from_irq() function.

I found that the first time backend driver got irq,
the irq number was 0.
Calling info_for_irq() function in evtchn_from_irq() with irq 0 returns NULL,
and that was the cause of null pointer deference kernel panic.

I circumvented it by not calling notify_remote_via_irq when irq is 0,
and the backend/frontend driver worked well.

I wonder if this is x86 specific behavior,
or a simple mistake on my end :)

>
> Jintack


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