Re: [PATCH v7 06/13] KVM: x86: Add Intel Processor Trace virtualization mode

[Paolo Bonzini]

On 03/05/2018 14:09, Alexander Shishkin wrote:
>>> 1. Do we have an event in pt_ctx?
>>>  * No -> Set up the context for VMX.
>>>  * Yes -> 2. Is attr.exclude_guest set?
>>>              * No -> Guest trace goes to the host's buffer, do nothing.
>>> 	     * Yes -> Set up/switch the context for VMX.
>> Can you explain this more clearly?
> Let's see; in the intel_pt driver we have a per-cpu PT "context", from which
> we can tell if there is a host event that wants to trace the guest. This
> should provide enough information to make a decision whether we want to
> context switch PT MSRs or not on the spot, instead of having a module
> parameter.

I still don't understand how the host event is useful...

Paolo