| Message ID | 20241001095734.11a67b4b@gandalf.local.home (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] Documentation/tracing: Mention that RESET_ATTACK_MITIGATION can clear memory | expand |
Jon, This version should be good to go. Thanks, -- Steve On Tue, 1 Oct 2024 09:57:34 -0400 Steven Rostedt <rostedt@goodmis.org> wrote: > From: Steven Rostedt <rostedt@goodmis.org> > > 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@linaro.org/ > > Reported-by: Hans de Goede <hdegoede@redhat.com> > Reviewed-by: Hans de Goede <hdegoede@redhat.com> > Acked-by: Ard Biesheuvel <ardb@kernel.org> > Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> > --- > Changes since v1: https://lore.kernel.org/20240926130159.19e6d0e2@rorschach.local.home > > - Added more detail explanation that the system may not be able to use > memory to preserve the tracing ring buffer across reboots and use > the CONFIG_RESET_ATTACK_MITIGATION as one example. > > Documentation/admin-guide/kernel-parameters.txt | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 1518343bbe22..9881e3b857d0 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -6867,6 +6867,12 @@ > > reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq > > + Note, saving the trace buffer across reboots does require that the system > + is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION > + can force a memory reset on boot which will clear any trace that was stored. > + This is just one of many ways that can clear memory. Make sure you system > + keeps the content of memory across reboots before relying on this option. > + > See also Documentation/trace/debugging.rst > >
Steven Rostedt <rostedt@goodmis.org> writes: > Jon, > > This version should be good to go. Applied, thanks. jon
On Mon, 07 Oct 2024 11:06:06 -0600 Jonathan Corbet <corbet@lwn.net> wrote: > Steven Rostedt <rostedt@goodmis.org> writes: > > > Jon, > > > > This version should be good to go. > > Applied, thanks. And I now see I sent an older version that had a typo in it :-p + Note, saving the trace buffer across reboots does require that the system + is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION + can force a memory reset on boot which will clear any trace that was stored. + This is just one of many ways that can clear memory. Make sure you system your system + keeps the content of memory across reboots before relying on this option. + I can send a v3. -- Steve
Steven Rostedt <rostedt@goodmis.org> writes: > On Mon, 07 Oct 2024 11:06:06 -0600 > Jonathan Corbet <corbet@lwn.net> wrote: > >> Steven Rostedt <rostedt@goodmis.org> writes: >> >> > Jon, >> > >> > This version should be good to go. >> >> Applied, thanks. > > And I now see I sent an older version that had a typo in it :-p > > > + Note, saving the trace buffer across reboots does require that the system > + is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION > + can force a memory reset on boot which will clear any trace that was stored. > + This is just one of many ways that can clear memory. Make sure you system > > your system > > + keeps the content of memory across reboots before relying on this option. > + > > I can send a v3. *Grumble... :) I haven't pushed out my tree yet, so I can replace the other one. jon
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 1518343bbe22..9881e3b857d0 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -6867,6 +6867,12 @@ reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq + Note, saving the trace buffer across reboots does require that the system + is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION + can force a memory reset on boot which will clear any trace that was stored. + This is just one of many ways that can clear memory. Make sure you system + keeps the content of memory across reboots before relying on this option. + See also Documentation/trace/debugging.rst