When an MTRR entry is inclusive to a requested range, i.e.
the start and end of the request are not within the MTRR
entry range but the range contains the MTRR entry entirely,
__mtrr_type_lookup() ignores such a case because both
start_state and end_state are set to zero.
This bug can cause the following issues:
1) reserve_memtype() tracks an effective memory type in case
a request type is WB (ex. /dev/mem blindly uses WB). Missing
to track with its effective type causes a subsequent request
to map the same range with the effective type to fail.
2) pud_set_huge() and pmd_set_huge() check if a requested range
has any overlap with MTRRs. Missing to detect an overlap may
cause a performance penalty or undefined behavior.
This patch fixes the bug by adding a new flag, 'inclusive',
to detect the inclusive case. This case is then handled in
the same way as end_state:1 since the first region is the same.
With this fix, __mtrr_type_lookup() handles the inclusive case
properly.
Signed-off-by: Toshi Kani <toshi.kani@xxxxxx>
---
arch/x86/kernel/cpu/mtrr/generic.c | 28 ++++++++++++++++++----------
1 file changed, 18 insertions(+), 10 deletions(-)
diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
index 5b23967..e202d26 100644
--- a/arch/x86/kernel/cpu/mtrr/generic.c
+++ b/arch/x86/kernel/cpu/mtrr/generic.c
@@ -154,7 +154,7 @@ static u8 __mtrr_type_lookup(u64 start, u64 end, u64 *partial_end, int *repeat)
prev_match = 0xFF;
for (i = 0; i < num_var_ranges; ++i) {
- unsigned short start_state, end_state;
+ unsigned short start_state, end_state, inclusive;
if (!(mtrr_state.var_ranges[i].mask_lo & (1 << 11)))
continue;
@@ -166,19 +166,27 @@ static u8 __mtrr_type_lookup(u64 start, u64 end, u64 *partial_end, int *repeat)
start_state = ((start & mask) == (base & mask));
end_state = ((end & mask) == (base & mask));
+ inclusive = ((start < base) && (end > base));
- if (start_state != end_state) {
+ if ((start_state != end_state) || inclusive) {
/*
* We have start:end spanning across an MTRR.
- * We split the region into
- * either
- * (start:mtrr_end) (mtrr_end:end)
- * or
- * (start:mtrr_start) (mtrr_start:end)
+ * We split the region into either
+ *
+ * - start_state:1
+ * (start:mtrr_end)(mtrr_end:end)
+ * - end_state:1
+ * (start:mtrr_start)(mtrr_start:end)
+ * - inclusive:1
+ * (start:mtrr_start)(mtrr_start:mtrr_end)(mtrr_end:end)
+ *
* depending on kind of overlap.
- * Return the type for first region and a pointer to
- * the start of second region so that caller will
- * lookup again on the second region.
+ *
+ * Return the type of the first region and a pointer
+ * to the start of next region so that caller will be
+ * advised to lookup again after having adjusted start
+ * and end.
+ *
* Note: This way we handle multiple overlaps as well.
*/
if (start_state)
--
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