x86/boot: Simplify EBDA-vs-BIOS reservation logic

[deliverable/linux.git] / arch / x86 / kernel / ebda.c

diff --git a/arch/x86/kernel/ebda.c b/arch/x86/kernel/ebda.c
index 6219eef20e2e7c8b33609bf9a895466cba5ca11c..4312f8ae71b78515885d8415ee5064034919b8d5 100644 (file)
--- a/arch/x86/kernel/ebda.c
+++ b/arch/x86/kernel/ebda.c
@@ -65,22 +65,6 @@ void __init reserve_bios_regions(void)
        if (!x86_platform.legacy.reserve_bios_regions)
                return;
 
-       /* Get the start address of the EBDA page: */
-       ebda_start = get_bios_ebda();
-
-       /*
-        * Quirk: some old Dells seem to have a 4k EBDA without
-        * reporting so in their BIOS RAM size value, so just
-        * consider the memory above 640K to be off limits
-        * (bugzilla 2990).
-        *
-        * We detect this case by filtering for nonsensical EBDA
-        * addresses below 128K, where we can assume that they
-        * are bogus and bump it up to a fixed 640K value:
-        */
-       if (ebda_start < BIOS_START_MIN)
-               ebda_start = BIOS_START_MAX;
-
        /*
         * BIOS RAM size is encoded in kilobytes, convert it
         * to bytes to get a first guess at where the BIOS
@@ -91,18 +75,22 @@ void __init reserve_bios_regions(void)
 
        /*
         * If bios_start is less than 128K, assume it is bogus
-        * and bump it up to 640K:
+        * and bump it up to 640K.  Similarly, if bios_start is above 640K,
+        * don't trust it.
         */
-       if (bios_start < BIOS_START_MIN)
+       if (bios_start < BIOS_START_MIN || bios_start > BIOS_START_MAX)
                bios_start = BIOS_START_MAX;
 
+       /* Get the start address of the EBDA page: */
+       ebda_start = get_bios_ebda();
+
        /*
-        * Use the lower of the bios_start and ebda_start
-        * as the starting point, but don't allow it to
-        * go beyond 640K:
+        * If the EBDA start address is sane and is below the BIOS region,
+        * then also reserve everything from the EBDA start address up to
+        * the BIOS region.
         */
-       bios_start = min(bios_start, ebda_start);
-       bios_start = min(bios_start, BIOS_START_MAX);
+       if (ebda_start >= BIOS_START_MIN && ebda_start < bios_start)
+               bios_start = ebda_start;
 
        /* Reserve all memory between bios_start and the 1MB mark: */
        memblock_reserve(bios_start, 0x100000 - bios_start);