NOVA, NUL, snapshotting

Julian Stecklina jsteckli at
Sun Aug 25 07:57:04 CEST 2013

"Sartakov A. Vasily" <sartakov at> schrieb:
>23.08.2013, в 15:23, Udo Steinberg <udo at> написал(а):
>> On Fri, 23 Aug 2013 15:13:35 +0400 Sartakov A. Vasily (SAV) wrote:
>> SAV> Could you please describe how to get access to a context of
>virtual machine? 
>> SAV> How can I modify context of virtual machine from Vancouver? 
>> SAV> When system switches into Vancouver, for example by pressing a
>special keyboard key, where is stored context of VM? in allocated VMCB?
>Can I read and modify its from Vancouver?
>> If you look at git/nul/vancouver/apps/vancouver/ you'll
>> functions like:
>> VM_FUNC(PT_VMX + 31,  vmx_rdmsr, MTD_RIP_LEN | MTD_GPR_ACDB | MTD_TSC
>>    handle_vcpu(pid, true, CpuMessage::TYPE_RDMSR, tls, utcb);)
>> This is the handler for VMX portal 31, which handles emulation of the
>> instruction (see NOVA specification Section 7.2 for a list of
>> The portal is configured to transfer a subset of the architectural
>> according to the MTD bits (see Section 7.4). The hypervisor stores
>> requested state into the UTCB, where the VMM can read and modify it.
>> 7.3 shows the layout of the UTCB with all the state fields.
>Thanks, now it is clear: NOVA can intercept commands from guest
>machine, then call VM functions via portal with saved state in UTCB. 
>I do not understand several things about messaging: 
>I see several reply functions and I know where they are called.
>for example:
>, +1659: 
>case MessageConsole::TYPE_START:
>And I see, that this message is send from function
>, +179:
>by calling msg1(MessageConsole::TYPE_START,  num -1);
>I hit a key, a key is processed by host driver, driver decides that
>this is a command for VM switching, host driver sends message to
>sigma0, sigma0 does something. 
>What about other commands, like MessageHostOp::OP_GET_MODULE? I see
>that all modules has a handler for this message, but I do not see who
>and how call them. 

This command is used by the vbios for Multiboot support. Check executor/

HTH, Julian

Sent from my phone. Please excuse my brevity.

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