[Qemu-devel] NMI handling

[Artyom Tarasenko]

2010/5/25 Blue Swirl <address@hidden>:
>>> About bugs, IIRC NetBSD 3.x crash could be related to IOMMU.
>>
>> What does indicate it? It happens where the disk sizes are normally
>> reported, so it could be a scsi/dma/irq/fpu issue as well.
>
> IIRC the DVMA address was 0xfc004000, but the mapped entries were for
> 0xfc000000 to 0xfc003fff.

Hmm. It happens in all NetBSD versions from 1.6 to 3.1 inclusive.
Which is probably a sign that the problem resides in qemu and not in
NetBSD.

It looks like we have multiple problems here: they start with
0xfc004000 access (which can theoretically be expected on the real
hardware too) as you pointed out, but what happens afterwards is
strange too:

- In the current qemu implementation we have a screaming NMI which
NetBSD can not clear. This happens cause NMI in qemu is literally
non-maskable, while on the real hardware it can be masked with the
'mask all' flag. I'll send a patch for it.

- with the masking patch, the NMI is not screaming but still is
percepted as spurious. This may be ok if NetBSD (1.6-3.1) doesn't have
a moduleerr_handler set. I don't see it set, although there is a
moduleerr_handler variable is defined. Would be nice if someone with
NetBSD kernel knowledge would comment on this.

- the current implementation of NMI pending clearing in qemu may be
incomplete: if the source is not cleared, the pending NMI bit can be
set right after the user wrote to the clear pending register. If I
read the page 39 of the Sun4m System Architecture correctly, the
points (2) and (6) suggest that once pending NMI is cleared in a CPU,
the CPU doesn't see the NMI till the next one comes. Whereas it makes
sense, specially in SMP configurations, I don't see how is it
level-sensitive in this case. If 'another broadcast' means a new
external event, the NMI behavior seems mixed: turned on by edge, and
off by level. But the documentation says 'level-sensitive' everywhere.
Ideas?

-- 
Regards,
Artyom Tarasenko

solaris/sparc under qemu blog: http://tyom.blogspot.com/