The sequence to move over to the Linux trap tables from
the firmware ones needs to be more air tight. It turns
out that to be %100 safe we do need to be able to translate
OBP mappings in our TLB miss handlers early.
In order not to eat up a lot of kernel image memory with
static page tables, just use the translations array in
the OBP TLB miss handlers. That solves the bulk of the
problem.
Furthermore, to make sure the OBP TLB miss path will work
even before the fixed MMU globals are loaded, explicitly
load %g1 to TLB_SFSR at the beginning of the i-TLB and
d-TLB miss handlers.
To ease the OBP TLB miss walking of the prom_trans[] array,
we sort it then delete all of the non-OBP entries in there
(for example, there are entries for the kernel image itself
which we're not interested in at all).
We also save about 32K of kernel image size with this change.
Not a bad side effect :-)
There are still some reasons why trampoline.S can't use the
setup_trap_table() yet. The most noteworthy are:
1) OBP boots secondary processors with non-bias'd stack for
some reason. This is easily fixed by using a small bootup
stack in the kernel image explicitly for this purpose.
2) Doing a firmware call via the normal C call prom_set_trap_table()
goes through the whole OBP enter/exit sequence that saves and
restores OBP and Linux kernel state in the MMUs. This path
unfortunately does a "flush %g6" while loading up the OBP locked
TLB entries for the firmware call.
If we setup the %g6 in the trampoline.S code properly, that
is in the PAGE_OFFSET linear mapping, but we're not on the
kernel trap table yet so those addresses won't translate properly.
One idea is to do a by-hand firmware call like we do in the
early bootup code and elsewhere here in trampoline.S But this
fails as well, as aparently the secondary processors are not
booted with OBP's special locked TLB entries loaded. These
are necessary for the firwmare to processes TLB misses correctly
up until the point where we take over the trap table.
This does need to be resolved at some point.
Signed-off-by: David S. Miller <davem@davemloft.net>
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
David S. Miller