tree ba1a4ca2bbc6d6ada1cae51239cec1cb952699df
parent 861f20cafb82431379ddde0aed3488fdfabfef80
author Barret Rhoden <brho@cs.berkeley.edu> 1513962384 -0500
committer Barret Rhoden <brho@cs.berkeley.edu> 1513962384 -0500

vmm: Handle mov with zero-extend

I noticed that if you dropped the apic=debug command line argument to the
guest, then they would crash.

The root cause was our EPT handler, which emulates access to the low 4K of
physical memory, wasn't handling movzwl correctly.  We were not
zero-extending.  That led to junk in registers that the compiler didn't
expect.  And that led Linux to get a false positive for get_bios_ebda(),
which lead to dereferencing garbage.

The apic=debug turned on a printk, which was enough to change the registers
so that the junk was not present.  Similarly, some basic tracing that moved
registers or changed "don't care" values before the call to get_bios_ebda()
was enough to make the code work.

Signed-off-by: Barret Rhoden <brho@cs.berkeley.edu>