Martin,
As Frank already said PATM/CSAM is completely disabled for VT-x and AMD-V.
There is limited patching for such modes, but it is separate as it's too
different from
the software virtualization (aka raw mode) mechanism. See
HWACCMR3PatchTprInstr in
src/VBox/VMM/HWACCM.cpp.
This patching works a little bit differently as it relies on the guest
additions to allocate a block of
executable memory to be used to store the patch code. It's not nearly as
powerful as PATM as
it only does simple code changes to optimize TPR APIC accesses inside
the guest.
Sander
On 4/15/2010 9:10 AM, Frank Mehnert wrote:
Hi Martim,
please ask such questions at the vbox-dev mailing list (see
http://www.virtualbox.org/mailman/listinfo/vbox-dev
for instructions how to subscribe) so more developers have a chance
to answer. Regarding your problem:
On Wednesday 14 April 2010, you wrote:
I am currently using Vbox OSE for a research project and was wondering
if I could ask you some questions regarding VBox internals.
Basically, my goal is to be able to run a VM with Intel VMX enabled,
but I would also like to have PATM/CSAM operational in order to patch
specific instructions of my choice in the guest OS's kernel. Is this
possible or would it require extensive modifications?
I guess the first question would be whether PATM/CSAM is used at all
when a guest is running with VMX enabled. If yes, then I guess it is
just a matter of modifying it so that it patches the relevant
instructions when analyzing the kernel code. If not, I guess I would
have to enable it somehow by modifying the code.
Given the size and complexity of VirtualBox's code, it would be great
if you could provide me some initial pointers on how to achieve this.
The raw mode (this is how we call the mode when VMX/AMD-V is disabled
and the guest code is handled by the CSAM/PATM) requires that a part of
VirtualBox (the hypervisor) is executed in the guest context. This
code runs at ring 0 while the guest code runs at ring 1 (kernel) / ring 3
(userland). Certain instructions of the guest code is replaced by the
PATM and the patches branch to the hypervisor to emulate privileged
instructions for the guest.
If VMX or AMD-V is enabled, the guest runs completely unmodified and there
is no code of the VirtualBox hypervisor which is executed in the guest
context. In fact CSAM and PATM are completely disabled if VMX/AMD-V is
active. So to answer your question: No, I don't think this is possible,
at least not without a major rewrite of the code.
Some basic overview of the VirtualBox architecture can be found here:
http://www.virtualbox.org/wiki/VirtualBox_architecture
Apart from this online documentation I think the only source of information
we can provide is the source code.
Kind regards,
Frank
--
Kind regards / Mit freundlichen Gruessen / Met vriendelijke groet
--
Sun Microsystems GmbH Sander van Leeuwen
Werkstrasse 24 Senior Staff Engineer, VirtualBox
71384 Weinstadt, Germany mailto:[email protected]
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