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authorSteven Rostedt <rostedt@goodmis.org>2006-11-14 10:57:46 -0500
committerAndi Kleen <andi@basil.nowhere.org>2006-11-14 10:57:46 -0500
commit51d67a488b53a5cc8401460480c124eaec71e2d4 (patch)
tree0b46aaced195f18da6be13416f668717527147cb /arch/x86_64
parent14679eb3c50897889ba62f9a37e3bcd8a205b5e7 (diff)
[PATCH] x86-64: shorten the x86_64 boot setup GDT to what the comment says
Stephen Tweedie, Herbert Xu, and myself have been struggling with a very nasty bug in Xen. But it also pointed out a small bug in the x86_64 kernel boot setup. The GDT limit being setup by the initial bzImage code when entering into protected mode is way too big. The comment by the code states that the size of the GDT is 2048, but the actual size being set up is much bigger (32768). This happens simply because of one extra '0'. Instead of setting up a 0x800 size, 0x8000 is set up. On bare metal this is fine because the CPU wont load any segments unless they are explicitly used. But unfortunately, this breaks Xen on vmx FV, since it (for now) blindly loads all the segments into the VMCS if they are less than the gdt limit. Since the real mode segments are around 0x3000, we are getting junk into the VMCS and that later causes an exception. Stephen Tweedie has written up a patch to fix the Xen side and will be submitting that to those folks. But that doesn't excuse the GDT limit being a magnitude too big. AK: changed to compute true gdt size in assembler, fixed comment Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Andi Kleen <ak@suse.de>
Diffstat (limited to 'arch/x86_64')
-rw-r--r--arch/x86_64/boot/setup.S5
1 files changed, 2 insertions, 3 deletions
diff --git a/arch/x86_64/boot/setup.S b/arch/x86_64/boot/setup.S
index c3bfd223ab49..770940cc0108 100644
--- a/arch/x86_64/boot/setup.S
+++ b/arch/x86_64/boot/setup.S
@@ -836,13 +836,12 @@ gdt:
836 .word 0x9200 # data read/write 836 .word 0x9200 # data read/write
837 .word 0x00CF # granularity = 4096, 386 837 .word 0x00CF # granularity = 4096, 386
838 # (+5th nibble of limit) 838 # (+5th nibble of limit)
839gdt_end:
839idt_48: 840idt_48:
840 .word 0 # idt limit = 0 841 .word 0 # idt limit = 0
841 .word 0, 0 # idt base = 0L 842 .word 0, 0 # idt base = 0L
842gdt_48: 843gdt_48:
843 .word 0x8000 # gdt limit=2048, 844 .word gdt_end-gdt-1 # gdt limit
844 # 256 GDT entries
845
846 .word 0, 0 # gdt base (filled in later) 845 .word 0, 0 # gdt base (filled in later)
847 846
848# Include video setup & detection code 847# Include video setup & detection code