On Thu, 26 Sep 2024 19:54:48 +0200 Hans de Goede <hdegoede@xxxxxxxxxx> wrote: > Hi, > > On 26-Sep-24 7:01 PM, Steven Rostedt wrote: > > From: Steven Rostedt <rostedt@xxxxxxxxxxx> > > > > At the 2024 Linux Plumbers Conference, I was talking with Hans de Goede > > about the persistent buffer to display traces from previous boots. He > > mentioned that UEFI can clear memory. In my own tests I have not seen > > this. He later informed me that it requires the config option: > > > > CONFIG_RESET_ATTACK_MITIGATION > > > > It appears that setting this will allow the memory to be cleared on boot > > up, which will definitely clear out the trace of the previous boot. > > > > Add this information under the trace_instance in kernel-parameters.txt > > to let people know that this can cause issues. > > > > Link: https://lore.kernel.org/all/20170825155019.6740-2-ard.biesheuvel@xxxxxxxxxx/ > > > > Reported-by: Hans de Goede <hdegoede@xxxxxxxxxx> > > Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx> > > Thanks, patch looks good to me: > > Reviewed-by: Hans de Goede <hdegoede@xxxxxxxxxx> Thanks, And I forgot to send this to the Documentation maintainers :-p Jon, could you take this? Do you need me to resend, or can you just pull it from lore? https://lore.kernel.org/linux-trace-kernel/20240926130159.19e6d0e2@xxxxxxxxxxxxxxxxxxxx/ -- Steve > > Regards, > > Hans > > > > > --- > > Documentation/admin-guide/kernel-parameters.txt | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > > index bb48ae24ae69..f9b79294f84a 100644 > > --- a/Documentation/admin-guide/kernel-parameters.txt > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > @@ -6850,6 +6850,9 @@ > > > > reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq > > > > + Note, CONFIG_RESET_ATTACK_MITIGATION can force a memory reset on boot which > > + will clear any trace that was stored. > > + > > See also Documentation/trace/debugging.rst > > > >
