Christian Ehrhardt wrote:
I took the trouble to bisect (manually) exactly which change in the new
boot code triggers this problem.
The problem is with the lgdt instruction. Apparently XEN does not keep
the contents of the 48-bit gdt_48 data structure that is passed to lgdt
in the XEN machine state. Instead it appears to save the _address_ of the
48-bit descriptor somewhere. Unfortunately this data happens to reside on the
stack and is probably no longer availiable at the time of the actual
protected mode jump.
This is most likely a XEN-bug but given that there is a on line patch
to work around this problem, the linux kernel should probably do this.
My fix is to make the gdt_48 description in setup_gdt static (in
setup_idt this is already the case). This allows the kernel to boot under
XEN-hvm again.
Would indeed be a Xen bug, and a pretty serious one too. Quite frankly,
it reflects some pretty fundamental misconceptions about how x86 works.
Sometimes it is a bit disappointing if quite some debuggin work results
in a on line patch :-) Pleae consider applying.
LOL, well, that's usually a good thing.
-hpa
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