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

["Andreas Färber" <afaerber@suse.de>]

Am 05.08.2013 15:31, schrieb Aurélien Jarno:
> On Mon, Aug 05, 2013 at 10:45:31AM +0200, Andreas Färber wrote:
>> 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 <hpoussin@reactos.org> 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?
>>
> 
> I have tried this patches, and they don't fix the problem.

Too bad. So what do you propose? Restoring #ifdef and using
empty_slot_init() have been suggested so far, any other concrete ideas?

Andreas

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