3 files changed, 133 insertions, 10 deletions

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 8a8afbdeb34e..600c9de237a0 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -604,6 +604,7 @@ void __init e820_mark_nosave_regions(unsigned long limit_pfn)
 struct early_res {
         u64 start, end;
         char name[16];
+        char overlap_ok;
 };
 static struct early_res early_res[MAX_EARLY_RES] __initdata = {
         { 0, PAGE_SIZE, "BIOS data page" },     /* BIOS data page */
@@ -640,7 +641,93 @@ static int __init find_overlapped_early(u64 start, u64 end)
         return i;
 }
 
-void __init reserve_early(u64 start, u64 end, char *name)
+/*
+ * Drop the i-th range from the early reservation map,
+ * by copying any higher ranges down one over it, and
+ * clearing what had been the last slot.
+ */
+static void __init drop_range(int i)
+{
+        int j;
+
+        for (j = i + 1; j < MAX_EARLY_RES && early_res[j].end; j++)
+                ;
+
+        memmove(&early_res[i], &early_res[i + 1],
+               (j - 1 - i) * sizeof(struct early_res));
+
+        early_res[j - 1].end = 0;
+}
+
+/*
+ * Split any existing ranges that:
+ *  1) are marked 'overlap_ok', and
+ *  2) overlap with the stated range [start, end)
+ * into whatever portion (if any) of the existing range is entirely
+ * below or entirely above the stated range.  Drop the portion
+ * of the existing range that overlaps with the stated range,
+ * which will allow the caller of this routine to then add that
+ * stated range without conflicting with any existing range.
+ */
+static void __init drop_overlaps_that_are_ok(u64 start, u64 end)
+{
+        int i;
+        struct early_res *r;
+        u64 lower_start, lower_end;
+        u64 upper_start, upper_end;
+        char name[16];
+
+        for (i = 0; i < MAX_EARLY_RES && early_res[i].end; i++) {
+                r = &early_res[i];
+
+                /* Continue past non-overlapping ranges */
+                if (end <= r->start || start >= r->end)
+                        continue;
+
+                /*
+                 * Leave non-ok overlaps as is; let caller
+                 * panic "Overlapping early reservations"
+                 * when it hits this overlap.
+                 */
+                if (!r->overlap_ok)
+                        return;
+
+                /*
+                 * We have an ok overlap.  We will drop it from the early
+                 * reservation map, and add back in any non-overlapping
+                 * portions (lower or upper) as separate, overlap_ok,
+                 * non-overlapping ranges.
+                 */
+
+                /* 1. Note any non-overlapping (lower or upper) ranges. */
+                strncpy(name, r->name, sizeof(name) - 1);
+
+                lower_start = lower_end = 0;
+                upper_start = upper_end = 0;
+                if (r->start < start) {
+                        lower_start = r->start;
+                        lower_end = start;
+                }
+                if (r->end > end) {
+                        upper_start = end;
+                        upper_end = r->end;
+                }
+
+                /* 2. Drop the original ok overlapping range */
+                drop_range(i);
+
+                i--;            /* resume for-loop on copied down entry */
+
+                /* 3. Add back in any non-overlapping ranges. */
+                if (lower_end)
+                        reserve_early_overlap_ok(lower_start, lower_end, name);
+                if (upper_end)
+                        reserve_early_overlap_ok(upper_start, upper_end, name);
+        }
+}
+
+static void __init __reserve_early(u64 start, u64 end, char *name,
+                                                int overlap_ok)
 {
         int i;
         struct early_res *r;
@@ -656,14 +743,55 @@ void __init reserve_early(u64 start, u64 end, char *name)
                       r->end - 1, r->name);
         r->start = start;
         r->end = end;
+        r->overlap_ok = overlap_ok;
         if (name)
                 strncpy(r->name, name, sizeof(r->name) - 1);
 }
 
+/*
+ * A few early reservtations come here.
+ *
+ * The 'overlap_ok' in the name of this routine does -not- mean it
+ * is ok for these reservations to overlap an earlier reservation.
+ * Rather it means that it is ok for subsequent reservations to
+ * overlap this one.
+ *
+ * Use this entry point to reserve early ranges when you are doing
+ * so out of "Paranoia", reserving perhaps more memory than you need,
+ * just in case, and don't mind a subsequent overlapping reservation
+ * that is known to be needed.
+ *
+ * The drop_overlaps_that_are_ok() call here isn't really needed.
+ * It would be needed if we had two colliding 'overlap_ok'
+ * reservations, so that the second such would not panic on the
+ * overlap with the first.  We don't have any such as of this
+ * writing, but might as well tolerate such if it happens in
+ * the future.
+ */
+void __init reserve_early_overlap_ok(u64 start, u64 end, char *name)
+{
+        drop_overlaps_that_are_ok(start, end);
+        __reserve_early(start, end, name, 1);
+}
+
+/*
+ * Most early reservations come here.
+ *
+ * We first have drop_overlaps_that_are_ok() drop any pre-existing
+ * 'overlap_ok' ranges, so that we can then reserve this memory
+ * range without risk of panic'ing on an overlapping overlap_ok
+ * early reservation.
+ */
+void __init reserve_early(u64 start, u64 end, char *name)
+{
+        drop_overlaps_that_are_ok(start, end);
+        __reserve_early(start, end, name, 0);
+}
+
 void __init free_early(u64 start, u64 end)
 {
         struct early_res *r;
-        int i, j;
+        int i;
 
         i = find_overlapped_early(start, end);
         r = &early_res[i];
@@ -671,13 +799,7 @@ void __init free_early(u64 start, u64 end)
                 panic("free_early on not reserved area: %llx-%llx!",
                          start, end - 1);
 
-        for (j = i + 1; j < MAX_EARLY_RES && early_res[j].end; j++)
-                ;
-
-        memmove(&early_res[i], &early_res[i + 1],
-               (j - 1 - i) * sizeof(struct early_res));
-
-        early_res[j - 1].end = 0;
+        drop_range(i);
 }
 
 void __init early_res_to_bootmem(u64 start, u64 end)
diff --git a/arch/x86/kernel/head.c b/arch/x86/kernel/head.c
index a727c0b9819c..a6816be01cd6 100644
--- a/arch/x86/kernel/head.c
+++ b/arch/x86/kernel/head.c
@@ -51,7 +51,7 @@ void __init reserve_ebda_region(void)
                 lowmem = 0x9f000;
 
         /* reserve all memory between lowmem and the 1MB mark */
-        reserve_early(lowmem, 0x100000, "BIOS reserved");
+        reserve_early_overlap_ok(lowmem, 0x100000, "BIOS reserved");
 }
 
 void __init reserve_setup_data(void)
diff --git a/include/asm-x86/e820.h b/include/asm-x86/e820.h
index 7c32df07bae4..13fa5a076aa2 100644
--- a/include/asm-x86/e820.h
+++ b/include/asm-x86/e820.h
@@ -88,6 +88,7 @@ extern unsigned long end_user_pfn;
 extern u64 find_e820_area(u64 start, u64 end, u64 size, u64 align);
 extern u64 find_e820_area_size(u64 start, u64 *sizep, u64 align);
 extern void reserve_early(u64 start, u64 end, char *name);
+extern void reserve_early_overlap_ok(u64 start, u64 end, char *name);
 extern void free_early(u64 start, u64 end);
 extern void early_res_to_bootmem(u64 start, u64 end);
 extern u64 early_reserve_e820(u64 startt, u64 sizet, u64 align);