[PATCH] i386: fix MTRR code

Until not so long ago, there were system log messages pointing to
inconsistent MTRR setup of the video frame buffer caused by the way vesafb
and X worked. While vesafb was fixed meanwhile, I believe fixing it there
only hides a shortcoming in the MTRR code itself, in that that code is not
symmetric with respect to the ordering of attempts to set up two (or more)
regions where one contains the other. In the current shape, it permits
only setting up sub-regions of pre-exisiting ones. The patch below makes
this symmetric.

While working on that I noticed a few more inconsistencies in that code,
namely
- use of 'unsigned int' for sizes in many, but not all places (the patch
  is converting this to use 'unsigned long' everywhere, which specifically
  might be necessary for x86-64 once a processor supporting more than 44
  physical address bits would become available)
- the code to correct inconsistent settings during secondary processor
  startup tried (if necessary) to correct, among other things, the value
  in IA32_MTRR_DEF_TYPE, however the newly computed value would never get
  used (i.e. stored in the respective MSR)
- the generic range validation code checked that the end of the
  to-be-added range would be above 1MB; the value checked should have been
  the start of the range
- when contained regions are detected, previously this was allowed only
  when the old region was uncacheable; this can be symmetric (i.e. the new
  region can also be uncacheable) and even further as per Intel's
  documentation write-trough and write-back for either region is also
  compatible with the respective opposite in the other

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 17 insertions, 11 deletions

diff --git a/arch/i386/kernel/cpu/mtrr/if.c b/arch/i386/kernel/cpu/mtrr/if.c
index 5ac051bb9d5..9753bc6a1f3 100644
--- a/arch/i386/kernel/cpu/mtrr/if.c
+++ b/arch/i386/kernel/cpu/mtrr/if.c
@@ -17,7 +17,7 @@ extern unsigned int *usage_table;
 
 #define FILE_FCOUNT(f) (((struct seq_file *)((f)->private_data))->private)
 
-static char *mtrr_strings[MTRR_NUM_TYPES] =
+static const char *const mtrr_strings[MTRR_NUM_TYPES] =
 {
     "uncachable",               /* 0 */
     "write-combining",          /* 1 */
@@ -28,7 +28,7 @@ static char *mtrr_strings[MTRR_NUM_TYPES] =
     "write-back",               /* 6 */
 };
 
-char *mtrr_attrib_to_str(int x)
+const char *mtrr_attrib_to_str(int x)
 {
         return (x <= 6) ? mtrr_strings[x] : "?";
 }
@@ -155,6 +155,7 @@ mtrr_ioctl(struct file *file, unsigned int cmd, unsigned long __arg)
 {
         int err = 0;
         mtrr_type type;
+        unsigned long size;
         struct mtrr_sentry sentry;
         struct mtrr_gentry gentry;
         void __user *arg = (void __user *) __arg;
@@ -235,15 +236,15 @@ mtrr_ioctl(struct file *file, unsigned int cmd, unsigned long __arg)
         case MTRRIOC_GET_ENTRY:
                 if (gentry.regnum >= num_var_ranges)
                         return -EINVAL;
-                mtrr_if->get(gentry.regnum, &gentry.base, &gentry.size, &type);
+                mtrr_if->get(gentry.regnum, &gentry.base, &size, &type);
 
                 /* Hide entries that go above 4GB */
-                if (gentry.base + gentry.size > 0x100000
-                    || gentry.size == 0x100000)
+                if (gentry.base + size - 1 >= (1UL << (8 * sizeof(gentry.size) - PAGE_SHIFT))
+                    || size >= (1UL << (8 * sizeof(gentry.size) - PAGE_SHIFT)))
                         gentry.base = gentry.size = gentry.type = 0;
                 else {
                         gentry.base <<= PAGE_SHIFT;
-                        gentry.size <<= PAGE_SHIFT;
+                        gentry.size = size << PAGE_SHIFT;
                         gentry.type = type;
                 }
 
@@ -273,8 +274,14 @@ mtrr_ioctl(struct file *file, unsigned int cmd, unsigned long __arg)
         case MTRRIOC_GET_PAGE_ENTRY:
                 if (gentry.regnum >= num_var_ranges)
                         return -EINVAL;
-                mtrr_if->get(gentry.regnum, &gentry.base, &gentry.size, &type);
-                gentry.type = type;
+                mtrr_if->get(gentry.regnum, &gentry.base, &size, &type);
+                /* Hide entries that would overflow */
+                if (size != (__typeof__(gentry.size))size)
+                        gentry.base = gentry.size = gentry.type = 0;
+                else {
+                        gentry.size = size;
+                        gentry.type = type;
+                }
                 break;
         }
 
@@ -353,8 +360,7 @@ static int mtrr_seq_show(struct seq_file *seq, void *offset)
         char factor;
         int i, max, len;
         mtrr_type type;
-        unsigned long base;
-        unsigned int size;
+        unsigned long base, size;
 
         len = 0;
         max = num_var_ranges;
@@ -373,7 +379,7 @@ static int mtrr_seq_show(struct seq_file *seq, void *offset)
                         }
                         /* RED-PEN: base can be > 32bit */ 
                         len += seq_printf(seq, 
-                                   "reg%02i: base=0x%05lx000 (%4liMB), size=%4i%cB: %s, count=%d\n",
+                                   "reg%02i: base=0x%05lx000 (%4luMB), size=%4lu%cB: %s, count=%d\n",
                              i, base, base >> (20 - PAGE_SHIFT), size, factor,
                              mtrr_attrib_to_str(type), usage_table[i]);
                 }