32-bit binaries failing in 64 bit guests after using vmport

[Soren Hansen <soren@ubuntu.com>]

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Esteemed kvm developers!

I've been trying to debug this bug

    https://bugs.launchpad.net/ubuntu/+source/kvm/+bug/219165

It originally revealed itself by failing to run grub (which is a 32 bit
binary) when installing Ubuntu from our live cd. It turned out to be a
more general problem of 32 bit binaries failing to run. The server
install worked like a charm. I eventually discovered that loading the
vmmouse driver triggered it and narrowed it down to the call to
kvm_load_registers in vmport_ioport_read. 

We're releasing on Thursday, and I needed a quick fix, so I reverted the
calls to kvm_{save,load}_registers in vmport_ioport_read to the old code
that simply saved the eax, ebx, ecx, edx, esi, and edi registers, but
I'm supposing kvm_{load,save}_registers really should work here.

I dug a bit further into the code and tried disabling various pieces of
the kvm_load_registers until it finally worked again. The problem seems
to only arise when the lstar msr is loaded. I've looked at the code, but
seeing as three days ago I didn't know there was such a thing as an
lstar msr, I'm finding myself getting stuck. :)

Any pointers in the right direction would be lovely.

-- 
Soren Hansen               | 
Virtualisation specialist  | Ubuntu Server Team
Canonical Ltd.             | http://www.ubuntu.com/

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