[MIPS] Fix aliasing bug in copy_to_user_page / copy_from_user_page

The current implementation uses a sequence of a cacheflush and a copy.
This is racy in case of a multithreaded debuggee and renders GDB
virtually unusable.

Aside this fixes a performance hog rendering access to /proc/cmdline very
slow and resulting in a enough cache stalls for the 34K AP/SP programming
model to make the bare metal code on the non-Linux VPE miss RT deadlines.

The main part of this patch was originally written by Ralf Baechle;
Atushi Nemoto did the the debugging.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/mips/mm/pgtable-64.c b/arch/mips/mm/pgtable-64.c
index 44b5e97fff65..8d600d307d5d 100644
--- a/arch/mips/mm/pgtable-64.c
+++ b/arch/mips/mm/pgtable-64.c
@@ -8,6 +8,7 @@
  */
 #include <linux/init.h>
 #include <linux/mm.h>
+#include <asm/fixmap.h>
 #include <asm/pgtable.h>
 
 void pgd_init(unsigned long page)
@@ -52,7 +53,17 @@ void pmd_init(unsigned long addr, unsigned long pagetable)
 
 void __init pagetable_init(void)
 {
+        unsigned long vaddr;
+        pgd_t *pgd_base;
+
         /* Initialize the entire pgd.  */
         pgd_init((unsigned long)swapper_pg_dir);
         pmd_init((unsigned long)invalid_pmd_table, (unsigned long)invalid_pte_table);
+
+        pgd_base = swapper_pg_dir;
+        /*
+         * Fixed mappings:
+         */
+        vaddr = __fix_to_virt(__end_of_fixed_addresses - 1) & PMD_MASK;
+        fixrange_init(vaddr, 0, pgd_base);
 }