> From: Steven Rostedt <[email protected]>
>
> 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 <[email protected]>
> Signed-off-by: Andi Kleen <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
note, it seems to me that i386 had this fix years ago already.
Ingo
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