[Xen-changelog] [xen-unstable] [HVM] Clarify the HVM e820 map. Also make it rather more

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kfraser@xxxxxxxxxxxxxxxxxxxxx
# Node ID ddc4bc24f07c9cf833b2099e79f5e23c49822ed9
# Parent  14dc20d98ee1478ad17abcbb24ae6dec46521178
[HVM] Clarify the HVM e820 map. Also make it rather more
conservative wrt the ACPI region. hvmloader should fix up
by freeing unused memory in the range 0xE0000-0x100000.
Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>
---
 tools/libxc/xc_hvm_build.c |   37 ++++++++++++++++++++++++++++++-------
 1 files changed, 30 insertions(+), 7 deletions(-)

diff -r 14dc20d98ee1 -r ddc4bc24f07c tools/libxc/xc_hvm_build.c
--- a/tools/libxc/xc_hvm_build.c        Thu Nov 09 14:23:24 2006 +0000
+++ b/tools/libxc/xc_hvm_build.c        Thu Nov 09 15:38:15 2006 +0000
@@ -66,23 +66,46 @@ static void build_e820map(void *e820_pag
         mem_size = HVM_BELOW_4G_RAM_END;
     }
 
+    /* 0x0-0x9F000: Ordinary RAM. */
     e820entry[nr_map].addr = 0x0;
     e820entry[nr_map].size = 0x9F000;
     e820entry[nr_map].type = E820_RAM;
     nr_map++;
 
+    /*
+     * 0x9F000-0x9F800: SMBIOS tables.
+     * 0x9FC00-0xA0000: Extended BIOS Data Area (EBDA).
+     * TODO: SMBIOS tables should be moved higher (>=0xE0000).
+     *       They are unusually low in our memory map: could cause problems?
+     */
     e820entry[nr_map].addr = 0x9F000;
     e820entry[nr_map].size = 0x1000;
     e820entry[nr_map].type = E820_RESERVED;
     nr_map++;
 
-    e820entry[nr_map].addr = 0xEA000;
-    e820entry[nr_map].size = 0x02000;
-    e820entry[nr_map].type = E820_ACPI;
-    nr_map++;
-
-    e820entry[nr_map].addr = 0xF0000;
-    e820entry[nr_map].size = 0x10000;
+    /*
+     * Following regions are standard regions of the PC memory map.
+     * They are not covered by e820 regions. OSes will not use as RAM.
+     * 0xA0000-0xC0000: VGA memory-mapped I/O. Not covered by E820.
+     * 0xC0000-0xE0000: 16-bit devices, expansion ROMs (inc. vgabios).
+     * TODO: hvmloader should free pages which turn out to be unused.
+     */
+
+    /*
+     * 0xE0000-0x0F0000: PC-specific area. We place ACPI tables here.
+     *                   We *cannot* mark as E820_ACPI, for two reasons:
+     *                    1. ACPI spec. says that E820_ACPI regions below
+     *                       16MB must clip INT15h 0x88 and 0xe801 queries.
+     *                       Our rombios doesn't do this.
+     *                    2. The OS is allowed to reclaim ACPI memory after
+     *                       parsing the tables. But our FACS is in this
+     *                       region and it must not be reclaimed (it contains
+     *                       the ACPI global lock!).
+     * 0xF0000-0x100000: System BIOS.
+     * TODO: hvmloader should free pages which turn out to be unused.
+     */
+    e820entry[nr_map].addr = 0xE0000;
+    e820entry[nr_map].size = 0x20000;
     e820entry[nr_map].type = E820_RESERVED;
     nr_map++;
 

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