was converted to use Mach VM for Net2/4.4BSD. The user segment table
pointer was originally stored in the PCB. When Mach VM came along,
however, it was also stored in the pmap, and loaded into the PCB in
pmap_activate(). pmap_activate() would then note that the PCB's USTP
was now in sync with the pmap's USTP, and the low-level context switch
code would use the value from the PCB.
However, pmap_activate() would also load the hardware MMU context if
the pmap was the current pmap (or, in the case where pmaps can be shared,
such as in NetBSD, if the proc was the current proc). The low-level
context switch code would then reload the hardware _again_ using the
USTP from the PCB.
However, the optimization of not calling pmap_activate() if "stchanged"
was false ended up causing some processes to use stale USTP values from
the PCB when the low-level context switch code reloaded the hardware!
This was noticed by using a real vfork(2) (which worked for some time
before failing, surprisingly!)
Since I'm hard pressed to find any real optimization here (since the
hardware was always reloaded once, sometimes twice!), the code now always
calls pmap_activate(), which uses the correct USTP value (the one in the
pmap). The PCB's USTP is now ignored, and should eventually be g/c'd.
Another optimization can actually be performed, and I have added a comment
describing what it is, but have not yet implemented it.
Also note that most of the loadustp() functions where actually incomplete.
This has been corrected. These functions should probably be split up into
MMU-specific operations, and called indirectly, rather than doing constant
run-time decision making based on values that will never change during the
course of a boot's lifetime.
it in initializing during autoconfig. Similar to sys/arch/sun3/dev/zs.c
revision 1.47. Ought to fix hangs at first tty access reported by
Johnny Lam, <jlbg+@andrew.cmu.edu>.
causes the MI interrupt handler to barf when we get a 5380 RST interrupt
while probing. Worse, the VIA latches the interrupt, so simply having
all interrupts disabled during autoconfig doesn't resolve the problem.
[I demonstrated the latter on a IIci, which erroneously reports a
reselection attempt(!) after autoconfig is complete. The latched
interrupt results from the SCSI bus reset we do when initializing the
bus.]
Since interrupts must be enabled during autoconfig anyway (sigh), test
to see if autoconfig has completed in sbc_irq_intr(). If not, we don't
pass the interrupt up to the MI interrupt handler. Also, make sure to
clear the VIA interrupt if we're servicing an unclaimed 5380 RST
interrupt.
Thanks to Bill Studenmund for providing the key insight needed to unlock
this problem.
interrupt properly on a SuperMac Spectrum/8 Series III, and thanks
to Dan McMahill for loaning the card to Paul.
I modified Paul's patch somewhat to change grfmv_intr_generic_{1,4}
to grfmv_intr_generic_write{1,4} and added grfmv_intr_generic_or4 to
handle this card.
deal with cheap CD-ROMs and other devices that do not appear to have
any way to enable parity generation. In the future, it might be nice
to have this configurable on a per-device basis with back-to-back
parity errors automatically disabling parity for the device. That
would require some MI changes.
* Handle unaligned and odd-length transfers.
This could probably be handled better in the future.
