95 lines
3.5 KiB
Diff
95 lines
3.5 KiB
Diff
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# HG changeset patch
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# User Paolo Bonzini <pbonzini@redhat.com>
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# Date 1358505311 -3600
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# Node ID 3b59a6c3e9b0fb5009bdfff97c8493bb9f0bec54
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# Parent 025f202f3022c30d1ec3b6ffcb72861c43a32cf7
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x86: find a better location for the real-mode trampoline
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On some machines, the location at 0x40e does not point to the beginning
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of the EBDA. Rather, it points to the beginning of the BIOS-reserved
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area of the EBDA, while the option ROMs place their data below that
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segment.
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For this reason, 0x413 is actually a better source than 0x40e to get
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the location of the real-mode trampoline. Xen was already using it
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as a second source, and this patch keeps that working. However, just
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in case, let's also fetch the information from the multiboot structure,
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where the boot loader should have placed it. This way we don't
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necessarily trust one of the BIOS or the multiboot loader more than
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the other.
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Retain the previous code, thus using the multiboot value only if it's
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sane but lower than the BDA computed one. Also use the full 32-bit
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mem_lower value and prefer MBI_MEMLIMITS over open coding it (requiring
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a slight adjustment to multiboot.h to make its constants actually
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usable in assembly code, which previously they were only meant to be).
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Signed-off-by: Jan Beulich <jbeulich@suse.com>
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Acked-by: Keir Fraser <keir@xen.org>
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Committed-by: Jan Beulich <jbeulich@suse.com>
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--- a/xen/arch/x86/boot/head.S
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+++ b/xen/arch/x86/boot/head.S
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@@ -88,6 +88,20 @@ __start:
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movzwl 0x413,%eax /* use base memory size on failure */
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shl $10-4,%eax
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1:
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+ /*
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+ * Compare the value in the BDA with the information from the
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+ * multiboot structure (if available) and use the smallest.
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+ */
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+ testb $MBI_MEMLIMITS,(%ebx)
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+ jz 2f /* not available? BDA value will be fine */
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+ mov 4(%ebx),%edx
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+ cmp $0x100,%edx /* is the multiboot value too small? */
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+ jb 2f /* if so, do not use it */
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+ shl $10-4,%edx
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+ cmp %eax,%edx /* compare with BDA value */
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+ cmovb %edx,%eax /* and use the smaller */
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+
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+2: /* Reserve 64kb for the trampoline */
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sub $0x1000,%eax
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/* From arch/x86/smpboot.c: start_eip had better be page-aligned! */
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--- a/xen/include/xen/multiboot.h
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+++ b/xen/include/xen/multiboot.h
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@@ -18,6 +18,7 @@
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#ifndef __MULTIBOOT_H__
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#define __MULTIBOOT_H__
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+#include "const.h"
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/*
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* Multiboot header structure.
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@@ -31,17 +32,17 @@
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/* The magic number passed by a Multiboot-compliant boot loader. */
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#define MULTIBOOT_BOOTLOADER_MAGIC 0x2BADB002
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-#define MBI_MEMLIMITS (1u<< 0)
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-#define MBI_BOOTDEV (1u<< 1)
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-#define MBI_CMDLINE (1u<< 2)
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-#define MBI_MODULES (1u<< 3)
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-#define MBI_AOUT_SYMS (1u<< 4)
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-#define MBI_ELF_SYMS (1u<< 5)
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-#define MBI_MEMMAP (1u<< 6)
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-#define MBI_DRIVES (1u<< 7)
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-#define MBI_BIOSCONFIG (1u<< 8)
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-#define MBI_LOADERNAME (1u<< 9)
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-#define MBI_APM (1u<<10)
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+#define MBI_MEMLIMITS (_AC(1,u) << 0)
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+#define MBI_BOOTDEV (_AC(1,u) << 1)
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+#define MBI_CMDLINE (_AC(1,u) << 2)
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+#define MBI_MODULES (_AC(1,u) << 3)
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+#define MBI_AOUT_SYMS (_AC(1,u) << 4)
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+#define MBI_ELF_SYMS (_AC(1,u) << 5)
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+#define MBI_MEMMAP (_AC(1,u) << 6)
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+#define MBI_DRIVES (_AC(1,u) << 7)
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+#define MBI_BIOSCONFIG (_AC(1,u) << 8)
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+#define MBI_LOADERNAME (_AC(1,u) << 9)
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+#define MBI_APM (_AC(1,u) << 10)
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#ifndef __ASSEMBLY__
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