x86: mtrr_cleanup: first 1M may be covered in var mtrrs

The first 1M is don't care when it comes to the variables MTRRs.
Cover it as WB as a heuristic approximation; this is generally what we
want to minimize the number of registers.

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c
index 9086b38fbabe..663e530e08e0 100644
--- a/arch/x86/kernel/cpu/mtrr/main.c
+++ b/arch/x86/kernel/cpu/mtrr/main.c
@@ -1293,6 +1293,15 @@ static int __init mtrr_cleanup(unsigned address_bits)
         }
         nr_range = x86_get_mtrr_mem_range(range, 0, extra_remove_base,
                                           extra_remove_size);
+        /*
+         * [0, 1M) should always be coverred by var mtrr with WB
+         * and fixed mtrrs should take effective before var mtrr for it
+         */
+        nr_range = add_range_with_merge(range, nr_range, 0,
+                                        (1ULL<<(20 - PAGE_SHIFT)) - 1);
+        /* sort the ranges */
+        sort(range, nr_range, sizeof(struct res_range), cmp_range, NULL);
+
         range_sums = sum_ranges(range, nr_range);
         printk(KERN_INFO "total RAM coverred: %ldM\n",
                range_sums >> (20 - PAGE_SHIFT));