tree f20f1c382cc5cb6f876043339c0b8a2ff8ba212b
parent 741d2b2f8d8f155c4960214fc40097eb143b6ef0
author Che-Liang Chiou <clchiou@google.com> 1282533644 +0800
committer Che-Liang Chiou <clchiou@google.com> 1282533644 +0800

Add fake e820 memory map entries to zeropage

BUG=chromium-os:4521
TEST=manual

This patch set adds two e820 memory map entries to kernel's zeropage to
trick kernel into booting; otherwise kernel will choke on missing e820
memory map.

The added e820 memory map entries should let kernel boot and should not
make the memory map differ from that without the added entries.

Test Procedure:
1. Boot your test machine and save dmesg output, referred to as LOG1.
2. Apply the following one-line patch and then compile and install
   kernel.
3. Apply this patch set and re-build zeropage on kernel partition.
4. Boot the test machine and save dmesg output, referred to as LOG2.

LOG1 would contain the following messages (the exactly addresses of
memory map should differ slightly).
...
[    0.000000] BIOS-provided physical RAM map:
[    0.000000] bootconsole [earlyser0] enabled
...
[    0.000000] modified physical RAM map:
[    0.000000]  modified: 0000000000000000 - 0000000000002000 (usable)
[    0.000000]  modified: 0000000000002000 - 0000000000006000 (reserved)
[    0.000000]  modified: 0000000000006000 - 000000000008f000 (usable)
[    0.000000]  modified: 000000000008f000 - 0000000000090000 (ACPI NVS)
[    0.000000]  modified: 0000000000090000 - 00000000000a0000 (usable)
[    0.000000]  modified: 0000000000100000 - 0000000000f00000 (usable)
[    0.000000]  modified: 0000000001000000 - 000000003f33f000 (usable)
[    0.000000]  modified: 000000003f33f000 - 000000003f4bf000 (reserved)
[    0.000000]  modified: 000000003f4bf000 - 000000003f5bf000 (ACPI NVS)
[    0.000000]  modified: 000000003f5bf000 - 000000003f5f7000 (ACPI data)
[    0.000000]  modified: 000000003f5f7000 - 000000003f600000 (usable)
[    0.000000]  modified: 00000000fed1c000 - 00000000fed20000 (reserved)
[    0.000000]  modified: 00000000ffc00000 - 0000000100000000 (reserved)

LOG2 would contain the following messages (the exactly addresses of
memory map should differ slightly).
...
[    0.000000] BIOS-provided physical RAM map:
[    0.000000]  BIOS-e820: 0000000000000000 - 0000000000001000 (usable)
[    0.000000]  BIOS-e820: 00000000fffff000 - 0000000100000000 (reserved)
[    0.000000] bootconsole [earlyser0] enabled
...
[    0.000000] modified physical RAM map:
[    0.000000]  modified: 0000000000000000 - 0000000000002000 (usable)
[    0.000000]  modified: 0000000000002000 - 0000000000006000 (reserved)
[    0.000000]  modified: 0000000000006000 - 000000000008f000 (usable)
[    0.000000]  modified: 000000000008f000 - 0000000000090000 (ACPI NVS)
[    0.000000]  modified: 0000000000090000 - 00000000000a0000 (usable)
[    0.000000]  modified: 0000000000100000 - 0000000000f00000 (usable)
[    0.000000]  modified: 0000000001000000 - 000000003f33f000 (usable)
[    0.000000]  modified: 000000003f33f000 - 000000003f4bf000 (reserved)
[    0.000000]  modified: 000000003f4bf000 - 000000003f5bf000 (ACPI NVS)
[    0.000000]  modified: 000000003f5bf000 - 000000003f5f7000 (ACPI data)
[    0.000000]  modified: 000000003f5f7000 - 000000003f600000 (usable)
[    0.000000]  modified: 00000000fed1c000 - 00000000fed20000 (reserved)
[    0.000000]  modified: 00000000ffc00000 - 0000000100000000 (reserved)

Test result:
1. Compare the first paragraph of excerpts from LOG1 and LOG2:
   This shows that the fake e820 memory map entries are successfully
   added.
2. Compare the second paragraphs of excerpts from LOG1 and LOG2:
   This shows that the added entries do not modify the memory map.

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 49706d0..c9075ee 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -425,7 +425,7 @@ static int __init append_e820_map(struct e820entry
*biosmap, int nr_map)
 {
        /* Only one memory region (or negative)? Ignore it */
        if (nr_map < 2)
-               return no_e820_map_return();
+               return -1;

        return __append_e820_map(biosmap, nr_map);
 }

Review URL: http://codereview.chromium.org/3176019