1 files changed, 77 insertions, 7 deletions

diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
index 14f4f0c0329a..9f27228ceffd 100644
--- a/arch/x86/kernel/cpu/mtrr/generic.c
+++ b/arch/x86/kernel/cpu/mtrr/generic.c
@@ -64,6 +64,18 @@ static inline void k8_check_syscfg_dram_mod_en(void)
         }
 }
 
+/* Get the size of contiguous MTRR range */
+static u64 get_mtrr_size(u64 mask)
+{
+        u64 size;
+
+        mask >>= PAGE_SHIFT;
+        mask |= size_or_mask;
+        size = -mask;
+        size <<= PAGE_SHIFT;
+        return size;
+}
+
 /*
  * Check and return the effective type for MTRR-MTRR type overlap.
  * Returns 1 if the effective type is UNCACHEABLE, else returns 0
@@ -92,17 +104,19 @@ static int check_type_overlap(u8 *prev, u8 *curr)
 }
 
 /*
- * Returns the effective MTRR type for the region
- * Error returns:
- * - 0xFE - when the range is "not entirely covered" by _any_ var range MTRR
- * - 0xFF - when MTRR is not enabled
+ * Error/Semi-error returns:
+ * 0xFF - when MTRR is not enabled
+ * *repeat == 1 implies [start:end] spanned across MTRR range and type returned
+ *              corresponds only to [start:*partial_end].
+ *              Caller has to lookup again for [*partial_end:end].
  */
-u8 mtrr_type_lookup(u64 start, u64 end)
+static u8 __mtrr_type_lookup(u64 start, u64 end, u64 *partial_end, int *repeat)
 {
         int i;
         u64 base, mask;
         u8 prev_match, curr_match;
 
+        *repeat = 0;
         if (!mtrr_state_set)
                 return 0xFF;
 
@@ -153,8 +167,34 @@ u8 mtrr_type_lookup(u64 start, u64 end)
 
                 start_state = ((start & mask) == (base & mask));
                 end_state = ((end & mask) == (base & mask));
-                if (start_state != end_state)
-                        return 0xFE;
+
+                if (start_state != end_state) {
+                        /*
+                         * 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)
+                         * 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.
+                         * Note: This way we handle multiple overlaps as well.
+                         */
+                        if (start_state)
+                                *partial_end = base + get_mtrr_size(mask);
+                        else
+                                *partial_end = base;
+
+                        if (unlikely(*partial_end <= start)) {
+                                WARN_ON(1);
+                                *partial_end = start + PAGE_SIZE;
+                        }
+
+                        end = *partial_end - 1; /* end is inclusive */
+                        *repeat = 1;
+                }
 
                 if ((start & mask) != (base & mask))
                         continue;
@@ -180,6 +220,36 @@ u8 mtrr_type_lookup(u64 start, u64 end)
         return mtrr_state.def_type;
 }
 
+/*
+ * Returns the effective MTRR type for the region
+ * Error return:
+ * 0xFF - when MTRR is not enabled
+ */
+u8 mtrr_type_lookup(u64 start, u64 end)
+{
+        u8 type, prev_type;
+        int repeat;
+        u64 partial_end;
+
+        type = __mtrr_type_lookup(start, end, &partial_end, &repeat);
+
+        /*
+         * Common path is with repeat = 0.
+         * However, we can have cases where [start:end] spans across some
+         * MTRR range. Do repeated lookups for that case here.
+         */
+        while (repeat) {
+                prev_type = type;
+                start = partial_end;
+                type = __mtrr_type_lookup(start, end, &partial_end, &repeat);
+
+                if (check_type_overlap(&prev_type, &type))
+                        return type;
+        }
+
+        return type;
+}
+
 /* Get the MSR pair relating to a var range */
 static void
 get_mtrr_var_range(unsigned int index, struct mtrr_var_range *vr)