[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, 5 insertions, 4 deletions

diff --git a/arch/i386/kernel/cpu/mtrr/centaur.c b/arch/i386/kernel/cpu/mtrr/centaur.c
index 33f00ac314e..cb9aa3a7a7a 100644
--- a/arch/i386/kernel/cpu/mtrr/centaur.c
+++ b/arch/i386/kernel/cpu/mtrr/centaur.c
@@ -17,7 +17,7 @@ static u8 centaur_mcr_type;	/* 0 for winchip, 1 for winchip2 */
  */
 
 static int
-centaur_get_free_region(unsigned long base, unsigned long size)
+centaur_get_free_region(unsigned long base, unsigned long size, int replace_reg)
 /*  [SUMMARY] Get a free MTRR.
     <base> The starting (base) address of the region.
     <size> The size (in bytes) of the region.
@@ -26,10 +26,11 @@ centaur_get_free_region(unsigned long base, unsigned long size)
 {
 	int i, max;
 	mtrr_type ltype;
-	unsigned long lbase;
-	unsigned int lsize;
+	unsigned long lbase, lsize;
 
 	max = num_var_ranges;
+	if (replace_reg >= 0 && replace_reg < max)
+		return replace_reg;
 	for (i = 0; i < max; ++i) {
 		if (centaur_mcr_reserved & (1 << i))
 			continue;
@@ -49,7 +50,7 @@ mtrr_centaur_report_mcr(int mcr, u32 lo, u32 hi)
 
 static void
 centaur_get_mcr(unsigned int reg, unsigned long *base,
-		unsigned int *size, mtrr_type * type)
+		unsigned long *size, mtrr_type * type)
 {
 	*base = centaur_mcr[reg].high >> PAGE_SHIFT;
 	*size = -(centaur_mcr[reg].low & 0xfffff000) >> PAGE_SHIFT;