[POWERPC] Fix 32-bit mm operations when not using BATs

On hash table based 32 bits powerpc's, the hash management code runs with
a big spinlock. It's thus important that it never causes itself a hash
fault. That code is generally safe (it does memory accesses in real mode
among other things) with the exception of the actual access to the code
itself. That is, the kernel text needs to be accessible without taking
a hash miss exceptions.

This is currently guaranteed by having a BAT register mapping part of the
linear mapping permanently, which includes the kernel text. But this is
not true if using the "nobats" kernel command line option (which can be
useful for debugging) and will not be true when using DEBUG_PAGEALLOC
implemented in a subsequent patch.

This patch fixes this by pre-faulting in the hash table pages that hit
the kernel text, and making sure we never evict such a page under hash
pressure.

Signed-off-by: Benjamin Herrenchmidt <benh@kernel.crashing.org>

 arch/powerpc/mm/hash_low_32.S |   22 ++++++++++++++++++++--
 arch/powerpc/mm/mem.c         |    3 ---
 arch/powerpc/mm/mmu_decl.h    |    4 ++++
 arch/powerpc/mm/pgtable_32.c  |   11 +++++++----
 4 files changed, 31 insertions(+), 9 deletions(-)
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 0 insertions, 3 deletions

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 52f397c108a..c4bcd754642 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -58,9 +58,6 @@ int init_bootmem_done;
 int mem_init_done;
 unsigned long memory_limit;
 
-extern void hash_preload(struct mm_struct *mm, unsigned long ea,
-			 unsigned long access, unsigned long trap);
-
 int page_is_ram(unsigned long pfn)
 {
 	unsigned long paddr = (pfn << PAGE_SHIFT);