Re: [PATCH v9 06/12] KVM: x86: Add Intel Processor Trace virtualization mode

From: Paolo Bonzini
Date: Mon Jun 11 2018 - 07:40:01 EST

On 07/06/2018 15:26, Alexander Shishkin wrote:
>> Intel PT virtualization can be work in one of 2 possible modes:
>> a. system-wide: trace both host and guest and output to host buffer;
>> b. host-guest: trace host/guest simultaneous and output to their
>> respective buffer.
> I think we discussed this before. That's not the choice that the user
> needs to make. The only choice that I see is what happens if the guest
> wants to use PT while it's already in use by the host. Otherwise, each
> of them gets to use PT as they would.

That is a superset of this choice:

a. hide PT from guests completely (the "a" above)

b. host-guest with guest preference: same as "b" above

c. host-guest with host preference: trace host/guest simultaneously, but
drop guest events if the host has tracing enabled.

so I don't think this choice is an issue.