Re: [Qemu-devel] [Qemu devel v9 PATCH 2/5] msf2: Microsemi Smartfusion2 System Register block

[Peter Maydell]

On 18 September 2017 at 14:58, Philippe Mathieu-Daudé <address@hidden> wrote:
> Hi Peter,
>
> On 09/18/2017 10:36 AM, Peter Maydell wrote:
>>
>> On 18 September 2017 at 14:27, sundeep subbaraya <address@hidden>
>> wrote:
>>>>>
>>>>> Hi Sundeep, Peter,
>>>>>
>>>>>
>>>>> On 09/15/2017 01:59 PM, Subbaraya Sundeep wrote:
>>>>>>
>>>>>>
>>>>>> +static void msf2_sysreg_write(void *opaque, hwaddr offset,
>>>>>> +                          uint64_t val, unsigned size)
>>>>>> +{
>>>>>> +    MSF2SysregState *s = opaque;
>>>>>> +    uint32_t newval = val;
>>>>>> +
>>>>>> +    offset >>= 2;
>>>>>> +
>>>>>> +    switch (offset) {
>>>>>> +    case MSSDDR_PLL_STATUS:
>>>>>> +        trace_msf2_sysreg_write_pll_status();
>>>>>> +        break;
>>>>>> +
>>>>>> +    case ESRAM_CR:
>>>>>> +    case DDR_CR:
>>>>>> +    case ENVM_REMAP_BASE_CR:
>>>>>> +        if (newval != s->regs[offset]) {
>>>>>> +            qemu_log_mask(LOG_UNIMP,
>>>>>> +                       TYPE_MSF2_SYSREG": remapping not
>>>>>> supported\n");
>>>>>
>>>>>
>>>>>
>>>>> I'd rather exit here than continue with inconsistent cpu, Peter what do
>>>>> you recommend?
>>>
>>>
>>>
>>> Could you please suggest.
>>
>>
>> We shouldn't exit QEMU for something the guest can provoke. If
>> the functionality isn't implemented then just LOG_UNIMP it.
>
>
> This was commented here:
> http://lists.nongnu.org/archive/html/qemu-devel/2017-05/msg02971.html
>
> Guest remapping code is like non-return function. Hardware error here can
> not happen, so there is no more guest code after a remap request.
> Continuing running QEMU will lead to chaos, that's why I recommend aborting
> instead of just LOG_UNIMP it.

There's lots of stuff that can cause the guest to go badly
and confusingly wrong if unimplemented. If we print a
useful message with LOG_UNIMP then there's an easy clue
for what's gone wrong. The guest shouldn't be able to
provoke QEMU to exit.

thanks
-- PMM