Problem with virtual to physical memory translation when KVM is enabled.

[Wayne Li]

Dear KVM list members,

We developed a virtual machine using the QEMU code.  This virtual
machine emulates a certain custom-made computer that runs on a certain
military platform.  All I can tell you about this virtual machine is
that it emulates a computer that has an e5500 processor.  Currently I
am running this virtual machine on a T4240-RDB which has a PowerPC
e6500 processor.

Anyway, right now I’m trying to get this virtual machine working with
KVM enabled.  But the problem I’m having is the VM doesn’t do anything
after the KVM_RUN ioctl call is made (NIP doesn’t progress and no
registers change).  What seems to be the problem is the VM doesn’t run
the instruction that’s supposed to be retrieved from the virtual
address 0xFFFF_FFFC.   When KVM isn’t enabled and the VM is running
using TCG (tiny code generator), a branch instruction to 0xFFFF_F700
is retrieved from the virtual address 0xFFFF_FFFC and the VM kicks off
running from there.

So what could be causing this problem?  I’m guessing it has something
to do with the translation lookaside buffers (TLBs)?  But the
translation between virtual and physical memory clearly works when KVM
isn’t enabled.  So what could cause this to stop working when KVM is
enabled?  Or maybe I’m not understanding something right and missing
what the problem actually is?  Let me know your thoughts.

-Thanks, Wayne Li