Re: [PATCH] coresight: etm4x: Add config to exclude kernel mode tracing

Suzuki Poulose
2020-10-16T13:17:58Z

On 10/16/20 2:14 PM, Leo Yan wrote:
> On Fri, Oct 16, 2020 at 12:38:47PM +0100, Suzuki Kuruppassery Poulose wrote:
>
> [...]
>
>>>> What happens to the sysfs mode of tracing? For that we would still
>>>> need a config right to exclude kernel mode tracing completely.
>>>
>>> IIUC, sysfs mode and perf mode both can apply the same approach, the
>>> guest OS runs a thread context for the host, so when a guest OS is
>>> switched in or out, the hypervisor can save/restore the context for
>>> the guest OS; thus every guest OS will have its dedicated context and
>>> trace data ideally.
>>
>> I don't think Guest Context is something we can support as mentioned
>> above, at least for systems without sysreg access for ETMs (and virtualizing
>> ETRs is a different story !)
>
> Thanks for sharing thoughts, Suzuki.
>
> I missed the device virtulisation. Here should virtualize all devices
> (includes CoreSight ETM/funnel/ETR/ETF)? Or only need to virtualize
> ETRs?

I wouldn't even think of virtualizing the components without sysreg
access. So let us not worry about it :-)

Cheers
Suzuki