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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> |
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