Re: [Qemu-devel] [PATCH for-1.6] target-mips: do not raise exceptions when accessing invalid memory

[Andreas Färber]

Am 05.08.2013 00:04, schrieb Aurélien Jarno:
> On Mon, Jul 29, 2013 at 10:35:31PM +0200, Stefan Weil wrote:
>> Am 27.07.2013 22:58, schrieb Stefan Weil:
>>> Am 27.07.2013 22:43, schrieb Andreas Färber:
>>>> Am 27.07.2013 21:37, schrieb Stefan Weil:
>>>>> Am 27.07.2013 19:43, schrieb Peter Maydell:
>>>>>> On 27 July 2013 17:18, Hervé Poussineau <address@hidden> wrote:
>>>>>>> Another solution would be to add a big dummy memory regions on all MIPS 
>>>>>>> boards
>>>>>>> to catch memory accesses and not raise an exception. However, this 
>>>>>>> means that
>>>>>>> each MIPS board will have its own unassigned memory handler, different 
>>>>>>> from the
>>>>>>> global QEMU one.
>>>>>> Better would be to at least provide fake RAZ/WI implementations of
>>>>>> devices for the boards, rather than making the dummy region cover
>>>>>> the whole of the address space. Not 1.6 material, though.
>>
>>
>> For MIPS Malta, Linux boot can be fixed by handling read access for two
>> addresses:
>>
>> 0x1fbf8008
>> 0x1bc80110
>>
>> The corresponding definitions in the Linux kernel code seem to be these
>> lines:
>>
>> #define GCMP_BASE_ADDR                  0x1fbf8000
>> #define GCMP_ADDRSPACE_SZ               (256 * 1024)
>> #define GCMP_GCB_GCMPB_OFS              0x0008          /* Global GCMP
>> Base */
>>
>> #define MSC01_BIU_REG_BASE              0x1bc80000
>> #define MSC01_BIU_ADDRSPACE_SZ          (256 * 1024)
>> #define MSC01_SC_CFG_OFS                0x0110
>>
>> => mips_malta.c needs a handler for reads of
>> (GCMP_BASE_ADDR + GCMP_GCB_GCMPB_OFS) and
>> (MSC01_BIU_REG_BASE + MSC01_SC_CFG_OFS).
> 
> I don't think it would be correct to emulate them as this are not
> present on the real Malta board, at least for the model emulated by
> QEMU. Theses addresses correspond to the SMP controller, and is
> therefore only present when an SMP daughter card is installed.
> 
> The Linux kernel probes theses addresses, and look if they return
> something consistent. If not the corresponding devices are latter
> ignored.
> 
> The real hardware probably returns all 1 or all 0 for addresses not
> decoded to a device. This is what QEMU should model, and it should
> not trigger a DBE or IBE exception.
[snip]

Have you tested Jan's patches limiting the new unassigned read value -1
to PIO?

Andreas

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