Re: [PATCH] x86/tsc: Add debugfs entry to mark TSC as unstable after boot

[H. Peter Anvin]

On March 17, 2025 7:35:45 AM PDT, "Guilherme G. Piccoli" <gpiccoli@xxxxxxxxxx> wrote:
>On 26/02/2025 10:27, Guilherme G. Piccoli wrote:
>> Right now, we can force the TSC to be marked as unstable through
>> boot parameter. There are debug / test cases though in which would
>> be preferable to simulate the clocksource watchdog behavior, i.e.,
>> marking TSC as unstable during the system run. Some paths might
>> change, for example: the tracing clock is auto switched to global
>> if TSC is marked as unstable on boot, but it could remain local if
>> TSC gets marked as unstable after tracing initialization.
>> 
>> Hence, the proposal here is to have a simple debugfs file that
>> gets TSC marked as unstable when written.
>> 
>> Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx>
>> ---
>>  arch/x86/kernel/tsc.c | 22 ++++++++++++++++++++++
>>  1 file changed, 22 insertions(+)
>
>Hi folks, gentle ping about this one - any suggestions?
>Cheers,
>
>
>Guilherme

To be honest I don't think this belongs in debugfs; rather it belongs in sysfs.

Debugfs should not be necessarily in serious production systems – it is way too large of an attack surface, which is a very good reason why it is its own filesystem – but if this is a real issue on hardware then it may be needed.

   -hpa