Re: [PATCH] KVM: nVMX: nSVM: Show guest mode in kvm_{entry,exit} tracepoints

[Krish Sadhukhan <krish.sadhukhan@oracle.com>]

On 8/2/21 9:39 AM, Paolo Bonzini wrote:
> On 02/08/21 18:34, Sean Christopherson wrote:
>> On Mon, Aug 02, 2021, Paolo Bonzini wrote:
>>> On 21/06/21 22:43, Krish Sadhukhan wrote:
>>>> With this patch KVM entry and exit tracepoints will
>>>> show "guest_mode = 0" if it is a guest and "guest_mode = 1" if it is a
>>>> nested guest.
>>>
>>> What about adding a "(nested)" suffix for L2, and nothing for L1?
>>
>> That'd work too, though it would be nice to get vmcx12 printed as 
>> well so that
>> it would be possible to determine which L2 is running without having 
>> to cross-
>> reference other tracepoints.
>
> Yes, it would be nice but it would also clutter the output a bit.
> It's like what we have already in kvm_inj_exception:
>
>         TP_printk("%s (0x%x)",
>                   __print_symbolic(__entry->exception, 
> kvm_trace_sym_exc),
>                   /* FIXME: don't print error_code if not present */
>                   __entry->has_error ? __entry->error_code : 0)
>
> It could be done with a trace-cmd plugin, but that creates other 
> issues since
> it essentially forces the tracepoints to have a stable API.
>
> Paolo


Also, the vmcs/vmcb address is vCPU-specific, so if L2 runs on 10 vCPUs, 
traces will show 10 different addresses for the same L2 and it's not 
convenient on a cloud host where hundreds of L1s and L2s run. IMHO, the 
cleanest solution is if the hardware vendors can provide a UUID space in 
the VMCS/VMCB itself. Today, we can print the UUID of L1 (by getting it 
from QEMU), but there's no way we can find out the one of L2.

OK, for now, I will add "nested" for L2 and nothing for L1.