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 <yhlu.kernel@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
index 509bd3d..43102e0 100644 (file)
--- a/arch/x86/kernel/cpu/mtrr/generic.c
+++ b/arch/x86/kernel/cpu/mtrr/generic.c
@@ -379,6 +379,7 @@ static void generic_get_mtrr(unsigned int reg, unsigned long *base,
                             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) {
@@ -392,8 +393,18 @@ static void generic_get_mtrr(unsigned int reg, unsigned long *base,
        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. */