Re: [Qemu-devel] [PATCH V2 1/2] ARM: PL061: Clear PL061 device state after reset

[Wei Huang <wei@redhat.com>]

On 02/16/2016 08:39 AM, Peter Maydell wrote:
> On 16 February 2016 at 14:35, Peter Maydell <peter.maydell@linaro.org> wrote:
>> On 1 February 2016 at 20:49, Wei Huang <wei@redhat.com> wrote:
>>> Current QEMU doesn't clear PL061 state after reset. This causes a
>>> weird issue with guest reboot via GPIO. Here is the device state
>>> description with two reboot requests:
> 
>>
>> These reset values are all OK...
>>
>>> +
>>> +static void pl061_state_reset(DeviceState *dev)
>>> +{
>>> +    PL061State *s = PL061(dev);
>>> +
>>> +    pl061_reset(s);
>>>  }
>>
>> ...but you don't need to have this wrapper function.
>> You can just do the reset in a function called pl061_reset()
>> with the function signature we need for dc->reset.
>> The only place that currently calls the existing pl061_reset()
>> is the device's init function, and you can delete that call
>> because the Device framework automatically calls the dc->reset
>> function after device initialization.
> 
> I know this patch doesn't (by itself) fix the issues with guest
> reboot, but I think it is worth having anyway because not resetting
> the PL061 state is a genuine bug. Can you do a v3 and resend, please?
> 
> PS: please could you include a cover letter email next time round,
> since this is a multi patch series?

Done, please review.

> 
> Side note: half our "PL061" behaviour is actually specific
> to the TI variant in the Luminary, and for our plain old PL061
> we ought to restrict access to the registers that are Stellaris
> only. But that's a different bug and not a very major one.

Thanks for your suggestion. I was trying to fix it. The plan was to add
a new field rsvd_addr in "struct PL061State". Then in pl061_read() and
pl061_write(), we can check offset against [rsvd_addr, 0xfcc] (ignored
if inside).

While I was working on it, I realized that this is a benign issue. It is
true that PL061 device can access Luminary registers in the reserved
memory area. However QEMU doesn't use these Luminary registers anywhere
else other than pl061_read() and pl061_write(). It basically passes the
read/write requests through. I don't see a malicious driver can damage
device state. Thoughts?

Thanks,
-Wei

> 
> thanks
> -- PMM
>