QEMU KVM tracing and KVM toggling

QEMU KVM tracing and KVM toggling

[Michał Matoga]

Hi,

I'm working on system calls tracing using QEMU KVM.

1. Is it possible to force emulation of instructions when VM is running? 
Then I might be able to enable/disable KVM acceleration whenever I want to.

2. I know I can get full trace from QEMU without KVM (log in_asm). For 
example during booting kernel I collected log 
(https://www.dropbox.com/s/ho7ykw1rc2tl4eb/qemu.log). Of course, when I 
enable KVM, this method will not work. I used trace-cmd tool to collect 
KVM events (https://www.dropbox.com/s/nhvtztzilvepwt0/kvm.log) but KVM 
log contains only functions emulated by QEMU. Is there a possibility to 
know what functions are executed natively in CPU when KVM is enabled to 
get something like "full" log from QEMU without KVM?

Regards,
Michał

Re: QEMU KVM tracing and KVM toggling

[Paolo Bonzini]

Il 13/03/2014 20:27, Michał Matoga ha scritto:
>
> I'm working on system calls tracing using QEMU KVM.
>
> 1. Is it possible to force emulation of instructions when VM is running?
> Then I might be able to enable/disable KVM acceleration whenever I want to.
>
> 2. I know I can get full trace from QEMU without KVM (log in_asm). For
> example during booting kernel I collected log
> (https://www.dropbox.com/s/ho7ykw1rc2tl4eb/qemu.log). Of course, when I
> enable KVM, this method will not work. I used trace-cmd tool to collect
> KVM events (https://www.dropbox.com/s/nhvtztzilvepwt0/kvm.log) but KVM
> log contains only functions emulated by QEMU. Is there a possibility to
> know what functions are executed natively in CPU when KVM is enabled to
> get something like "full" log from QEMU without KVM?

No, neither is possible.  Consider that forcing emulation while KVM is 
running would be hundreds of times slower than execution on the actual 
processor.  It's simply too slow.

If you run QEMU with "-cpu host", you can use "perf" in the guest to see 
what's happening.  Of course it will only be a statistical profile, not 
the full trace.

Paolo