[PATCH] i386: fix buggy MTRR address checks

Fix checks that failed to realize that values are 4-kB-unit-sized (note the
format strings in this same diff context which *do* realize the unit size,
via appended "000"!).  Also fix an incorrect below-1MB area check (as
gathered from Jan Beulich's unapplied patch at
http://www.ussg.iu.edu/hypermail/linux/kernel/0411.1/1378.html ) Update
mtrr_add_page() docu to make 4-kB-sized calculation more obvious.

Given several further items mentioned in Jan's patch mail, all in all MTRR
code seems surprisingly buggy, for a surprisingly long period of time (many
years).  Further work/investigation would be useful.

TBD Note that my patch is pretty much UNTESTED, since I can only verify that it
TBD successfully boots my machine, but I cannot test against actual buggy
TBD hardware which would require these (formerly broken) checks.  Long -mm
TBD simmering would make sense, especially since these now-working checks might
TBD turn out to have adverse effects on unaffected hardware.

Signed-off-by: Andreas Mohr <andi@lisas.de>
Signed-off-by: Andi Kleen <ak@suse.de>
Acked-by: Jan Beulich <jbeulich@novell.com>
Cc: Andi Kleen <ak@muc.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>

2 files changed, 4 insertions, 4 deletions

diff --git a/arch/i386/kernel/cpu/mtrr/generic.c b/arch/i386/kernel/cpu/mtrr/generic.c
index 0b61eed8bbd8..ee8dc6753953 100644
--- a/arch/i386/kernel/cpu/mtrr/generic.c
+++ b/arch/i386/kernel/cpu/mtrr/generic.c
@@ -366,7 +366,7 @@ int generic_validate_add_page(unsigned long base, unsigned long size, unsigned i
                         printk(KERN_WARNING "mtrr: base(0x%lx000) is not 4 MiB aligned\n", base);
                         return -EINVAL;
                 }
-                if (!(base + size < 0x70000000 || base > 0x7003FFFF) &&
+                if (!(base + size < 0x70000 || base > 0x7003F) &&
                     (type == MTRR_TYPE_WRCOMB
                      || type == MTRR_TYPE_WRBACK)) {
                         printk(KERN_WARNING "mtrr: writable mtrr between 0x70000000 and 0x7003FFFF may hang the CPU.\n");
@@ -374,7 +374,7 @@ int generic_validate_add_page(unsigned long base, unsigned long size, unsigned i
                 }
         }
 
-        if (base + size < 0x100) {
+        if (base < 0x100) {
                 printk(KERN_WARNING "mtrr: cannot set region below 1 MiB (0x%lx000,0x%lx000)\n",
                        base, size);
                 return -EINVAL;
diff --git a/arch/i386/kernel/cpu/mtrr/main.c b/arch/i386/kernel/cpu/mtrr/main.c
index fff90bda4733..2b8b0b361ccb 100644
--- a/arch/i386/kernel/cpu/mtrr/main.c
+++ b/arch/i386/kernel/cpu/mtrr/main.c
@@ -263,8 +263,8 @@ static void set_mtrr(unsigned int reg, unsigned long base,
 
 /**
  *      mtrr_add_page - Add a memory type region
- *      @base: Physical base address of region in pages (4 KB)
- *      @size: Physical size of region in pages (4 KB)
+ *      @base: Physical base address of region in pages (in units of 4 kB!)
+ *      @size: Physical size of region in pages (4 kB)
  *      @type: Type of MTRR desired
  *      @increment: If this is true do usage counting on the region
  *