Re: [PATCH v1 0/7] Implement support for external IPT monitoring

[Michał Leszczyński <michal.leszczynski@xxxxxxx>]

----- 18 cze 2020 o 1:29, Kang, Luwei luwei.kang@xxxxxxxxx napisał(a):

>> > > How does KVM deal with this, do they insert/modify trace packets on
>> > > trapped and emulated instructions by the VMM?
>> >
>> > The KVM includes instruction decoder and
>> emulator(arch/x86/kvm/emulate.c), and the guest's memory can be set to
>> write-protect as well. But it doesn't support Intel PT packets software
>> emulator.
>> For KVM, the Intel PT feature will be exposed to KVM guest and KVM guest can
>> use Intel PT feature like native.
>> 
>> But if such feature is exposed to the guest for it's own usage, won't it be
>> missing packets for instructions emulated by the VMM?
> 
> If setting the guest's memory write-protect, I think yes.


Thus, I propose to leave it as it is right now. If somebody is purposely 
altering the VM state then he/she should consult not only the IPT but also 
understand what was done "in the meantime" by additional features, e.g. when 
something was altered by vm_event callback. As Tamas said previously, we 
usually just want to see certain path leading to vmexit.

Please also note that there is a PTWRITE instruction that could be used in the 
future in order to add custom payloads/hints to the PT trace, when needed.


> 
> Thanks,
> Luwei Kang
> 
>> 
> > Thanks, Roger.