The trick is that we do the kernel linear mapping TLB miss starting
with an instruction sequence like this:
ba,pt %xcc, kvmap_load
xor %g2, %g4, %g5
succeeded by an instruction sequence which performs a full page table
walk starting at swapper_pg_dir.
We first take over the trap table from the firmware. Then, using this
constant PTE generation for the linear mapping area above, we build
the kernel page tables for the linear mapping.
After this is setup, we patch that branch above into a "nop", which
will cause TLB misses to fall through to the full page table walk.
With this, the page unmapping for CONFIG_DEBUG_PAGEALLOC is trivial.
Signed-off-by: David S. Miller <davem@davemloft.net>
This was kind of ugly, and actually buggy. The bug was that
we didn't handle a machine with memory starting > 4GB. If
the 'prompmd' was allocated in physical memory > 4GB we'd
croak because the obp_iaddr_patch and obp_daddr_patch things
only supported a 32-bit physical address.
So fix this by just loading the appropriate values from two
variables in the kernel image, which is locked into the TLB
and thus accesses to them can't cause a recursive TLB miss.
Signed-off-by: David S. Miller <davem@davemloft.net>
David S. Miller