[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, 3 deletions

diff --git a/include/asm-mips/fixmap.h b/include/asm-mips/fixmap.h
index 6959bdb59310..02c8a13fc894 100644
--- a/include/asm-mips/fixmap.h
+++ b/include/asm-mips/fixmap.h
@@ -45,8 +45,16 @@
  * fix-mapped?
  */
 enum fixed_addresses {
+#define FIX_N_COLOURS 8
+        FIX_CMAP_BEGIN,
+#ifdef CONFIG_MIPS_MT_SMTC
+        FIX_CMAP_END = FIX_CMAP_BEGIN + (FIX_N_COLOURS * NR_CPUS),
+#else
+        FIX_CMAP_END = FIX_CMAP_BEGIN + FIX_N_COLOURS,
+#endif
 #ifdef CONFIG_HIGHMEM
-        FIX_KMAP_BEGIN, /* reserved pte's for temporary kernel mappings */
+        /* reserved pte's for temporary kernel mappings */
+        FIX_KMAP_BEGIN = FIX_CMAP_END + 1,
         FIX_KMAP_END = FIX_KMAP_BEGIN+(KM_TYPE_NR*NR_CPUS)-1,
 #endif
         __end_of_fixed_addresses
@@ -70,9 +78,9 @@ extern void __set_fixmap (enum fixed_addresses idx,
  * at the top of mem..
  */
 #if defined(CONFIG_CPU_TX39XX) || defined(CONFIG_CPU_TX49XX)
-#define FIXADDR_TOP     (0xff000000UL - 0x2000)
+#define FIXADDR_TOP     ((unsigned long)(long)(int)(0xff000000 - 0x20000))
 #else
-#define FIXADDR_TOP     (0xffffe000UL)
+#define FIXADDR_TOP     ((unsigned long)(long)(int)0xfffe0000)
 #endif
 #define FIXADDR_SIZE    (__end_of_fixed_addresses << PAGE_SHIFT)
 #define FIXADDR_START   (FIXADDR_TOP - FIXADDR_SIZE)