port-mips/44900: R5000/Rm5200 mips ports

[Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>]

>Number:         44900
>Category:       port-mips
>Synopsis:       R5000/Rm5200 mips ports
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    port-mips-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Apr 23 12:40:00 +0000 2011
>Originator:     Izumi Tsutsui
>Release:        NetBSD 5.99.48
>Organization:
>Environment:
System: NetBSD mirage 5.99.48
but also affected systems after the second mips64 merge
Architecture: mips
Machine: cobalt, sgimips
>Description:
On R5000 and Rm52xx machines (probably also VR41xx, i.e. all MIPS3 CPUs
except R4000/R4400 with virtual cache coherency exception hardware)
kernels don't work properly.

- misc RPC programs complain "clntudp_create: RPC: Program not registered"
- NFS file read ops get corrupted randomly (returns zeroed block etc)
- FFS file write ops sometimes get corrupted
 etc.

R4400 machines don't have the problem, so I guess this is caused by
VA cache aliases, which is handled by hardware on R4000/R4400.

>How-To-Repeat:
You can see the problems on multiuser with GENERIC kernels on
R5000 sgimips or Rm52xx cobalt machines.

This doesn't happen on gxemul, but I'm doubt the emulator emulates
VA cache index ops and its aliases.

>Fix:
Unknown. Check and handle more possible VA cache aliases in pmap.c etc?

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