x86: work around MTRR mask setting

Joshua Hoblitt reported that only 3 GB of his 16 GB of RAM is
usable. Booting with mtrr_show showed us the BIOS-initialized
MTRR settings - which are all wrong.

So the root cause is that the BIOS has not set the mask correctly:

> [ 0.429971] MSR00000200: 00000000d0000000
> [ 0.433305] MSR00000201: 0000000ff0000800
> should be ==> [ 0.433305] MSR00000201: 0000003ff0000800
>
> [ 0.436638] MSR00000202: 00000000e0000000
> [ 0.439971] MSR00000203: 0000000fe0000800
> should be ==> [ 0.439971] MSR00000203: 0000003fe0000800
>
> [ 0.443304] MSR00000204: 0000000000000006
> [ 0.446637] MSR00000205: 0000000c00000800
> should be ==> [ 0.446637] MSR00000205: 0000003c00000800
>
> [ 0.449970] MSR00000206: 0000000400000006
> [ 0.453303] MSR00000207: 0000000fe0000800
> should be ==> [ 0.453303] MSR00000207: 0000003fe0000800
>
> [ 0.456636] MSR00000208: 0000000420000006
> [ 0.459970] MSR00000209: 0000000ff0000800
> should be ==> [ 0.459970] MSR00000209: 0000003ff0000800

So detect this borkage and add the prefix 111.

Signed-off-by: Yinghai Lu <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/kernel/cpu/mtrr/generic.c

···
 			     unsigned long *size, mtrr_type *type)
 {
 	unsigned int mask_lo, mask_hi, base_lo, base_hi;
+	unsigned int tmp, hi;
 
 	rdmsr(MTRRphysMask_MSR(reg), mask_lo, mask_hi);
 	if ((mask_lo & 0x800) == 0) {
···
 	rdmsr(MTRRphysBase_MSR(reg), base_lo, base_hi);
 
 	/* Work out the shifted address mask. */
-	mask_lo = size_or_mask | mask_hi << (32 - PAGE_SHIFT)
-	    | mask_lo >> PAGE_SHIFT;
+	tmp = mask_hi << (32 - PAGE_SHIFT) | mask_lo >> PAGE_SHIFT;
+	mask_lo = size_or_mask | tmp;
+	/* Expand tmp with high bits to all 1s*/
+	hi = fls(tmp);
+	if (hi > 0) {
+		tmp |= ~((1<<(hi - 1)) - 1);
+
+		if (tmp != mask_lo) {
+			WARN_ON("mtrr: your BIOS has set up an incorrect mask, fixing it up.\n");
+			mask_lo = tmp;
+		}
+	}
 
 	/* This works correctly if size is a power of two, i.e. a
 	   contiguous range. */