[Xen-bugs] [Bug 1054] New: Current linux-2.6 git snapshots do not boot under HVM (possible bug in lgdt emulation)

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http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1054

           Summary: Current linux-2.6 git snapshots do not boot under HVM
                    (possible bug in lgdt emulation)
           Product: Xen
           Version: 3.0.3
          Platform: Unspecified
        OS/Version: Linux
            Status: NEW
          Severity: critical
          Priority: P2
         Component: HVM
        AssignedTo: xen-bugs@xxxxxxxxxxxxxxxxxxx
        ReportedBy: lk@xxxxxxx


Hi,

I tried to boot current linux2.6-git snapshots under HVM. These contain a
complete rewrite of the 16-bit startup code which does not work nicely with
XEN. I was able to work around this by patching linux kernel code but this is
probably a bug in XEN.

As far as I can tell the problem is with the emulation of lgdt in real mode.
The new setup code currently stores the 48-bit data structure that is passed to
lgdt on the stack where it is no longer availiable at the time the CS register
is loaded and the actual switch to protected mode happens.

As opposed to the actual descriptor table this should not be a problem because
that information should be loaded into the CPU at the time the lgdt instruction
is executed.

I made this data structure static and the boot went smoothly.

For full logs and more information please refer to the corresponding thread on
the linux kernel mailing list, especially those message:

Original report: http://marc.info/?l=linux-kernel&m=118848403809462&w=2
XEN-Logs and config: http://marc.info/?l=linux-kernel&m=118884447330490&w=2
Linux kernel patch: http://marc.info/?l=linux-kernel&m=118884447330490&w=2

   regards  Christian


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