Re: [PATCH v9 7/7] arm64: kgdb: Roundup cpus using the debug IPI

On 2023-08-07 11:28, Mark Rutland wrote:

On Thu, Jun 01, 2023 at 02:31:51PM -0700, Douglas Anderson wrote:

quoted

From: Sumit Garg <redacted>

Let's use the debug IPI for rounding up CPUs in kgdb. When the debug
IPI is backed by an NMI (or pseudo NMI) then this will let us debug
even hard locked CPUs. When the debug IPI isn't backed by an NMI then
this won't really have any huge benefit but it will still work.

Signed-off-by: Sumit Garg <redacted>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

Changes in v9:
- Remove fallback for when debug IPI isn't available.
- Renamed "NMI IPI" to "debug IPI" since it might not be backed by 
NMI.

 arch/arm64/kernel/ipi_debug.c |  5 +++++
 arch/arm64/kernel/kgdb.c      | 14 ++++++++++++++
 2 files changed, 19 insertions(+)

This looks fine to me, but I'd feel a bit happier if we had separate 
SGIs for
the backtrace and the KGDB callback as they're logically unrelated.

Well, we're a bit stuck here.

We have exactly *one* spare SGI with GICv3, as we lose 8 of them
to the secure side. One possibility would be to mux some of the
lesser used IPIs onto two SGIs (one with standard priority, and
one with NMI priority).

         M.
-- 
Jazz is not dead. It just smells funny...

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