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Message-ID: <20230824083012.v11.4.Ie6c132b96ebbbcddbf6954b9469ed40a6960343c@changeid>
Date: Thu, 24 Aug 2023 08:30:30 -0700
From: Douglas Anderson <dianders@...omium.org>
To: Mark Rutland <mark.rutland@....com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Sumit Garg <sumit.garg@...aro.org>,
Daniel Thompson <daniel.thompson@...aro.org>,
Marc Zyngier <maz@...nel.org>
Cc: "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
Ard Biesheuvel <ardb@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
kgdb-bugreport@...ts.sourceforge.net,
Lecopzer Chen <lecopzer.chen@...iatek.com>,
linux-perf-users@...r.kernel.org,
Masayoshi Mizuma <msys.mizuma@...il.com>,
Chen-Yu Tsai <wens@...e.org>,
linux-arm-kernel@...ts.infradead.org, ito-yuichi@...itsu.com,
Stephen Boyd <swboyd@...omium.org>,
Peter Zijlstra <peterz@...radead.org>,
Douglas Anderson <dianders@...omium.org>,
D Scott Phillips <scott@...amperecomputing.com>,
Ingo Molnar <mingo@...nel.org>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Valentin Schneider <vschneid@...hat.com>,
linux-kernel@...r.kernel.org
Subject: [PATCH v11 4/6] arm64: smp: Add arch support for backtrace using pseudo-NMI
Enable arch_trigger_cpumask_backtrace() support on arm64. This enables
things much like they are enabled on arm32 (including some of the
funky logic around NR_IPI, nr_ipi, and MAX_IPI) but with the
difference that, unlike arm32, we'll try to enable the backtrace to
use pseudo-NMI.
NOTE: this patch is a squash of the little bit of code adding the
ability to mark an IPI to try to use pseudo-NMI plus the little bit of
code to hook things up for kgdb. This approach was decided upon in the
discussion of v9 [1].
This patch depends on commit 36759e343ff9 ("nmi_backtrace: allow
excluding an arbitrary CPU") since that commit changed the prototype
of arch_trigger_cpumask_backtrace(), which this patch implements.
[1] https://lore.kernel.org/r/ZORY51mF4alI41G1@FVFF77S0Q05N
Co-developed-by: Sumit Garg <sumit.garg@...aro.org>
Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
Co-developed-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Douglas Anderson <dianders@...omium.org>
---
Changes in v11:
- Adjust comment about NR_IPI/MAX_IPI.
- Don't use confusing "backed by" idiom in comment.
- Made arm64_backtrace_ipi() static.
Changes in v10:
- Backtrace now directly supported in smp.c
- Squash backtrace into patch adding support for pseudo-NMI IPIs.
Changes in v9:
- Added comments that we might not be using NMI always.
- Fold in v8 patch #10 ("Fallback to a regular IPI if NMI isn't enabled")
- Moved header file out of "include" since it didn't need to be there.
- Remove arm64_supports_nmi()
- Renamed "NMI IPI" to "debug IPI" since it might not be backed by NMI.
- arch_trigger_cpumask_backtrace() no longer returns bool
Changes in v8:
- Removed "#ifdef CONFIG_SMP" since arm64 is always SMP
- debug_ipi_setup() and debug_ipi_teardown() no longer take cpu param
arch/arm64/include/asm/irq.h | 3 ++
arch/arm64/kernel/smp.c | 86 +++++++++++++++++++++++++++++++-----
2 files changed, 78 insertions(+), 11 deletions(-)
diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h
index fac08e18bcd5..50ce8b697ff3 100644
--- a/arch/arm64/include/asm/irq.h
+++ b/arch/arm64/include/asm/irq.h
@@ -6,6 +6,9 @@
#include <asm-generic/irq.h>
+void arch_trigger_cpumask_backtrace(const cpumask_t *mask, int exclude_cpu);
+#define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace
+
struct pt_regs;
int set_handle_irq(void (*handle_irq)(struct pt_regs *));
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index a5848f1ef817..c8896cbc5327 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -33,6 +33,7 @@
#include <linux/kernel_stat.h>
#include <linux/kexec.h>
#include <linux/kvm_host.h>
+#include <linux/nmi.h>
#include <asm/alternative.h>
#include <asm/atomic.h>
@@ -72,12 +73,18 @@ enum ipi_msg_type {
IPI_CPU_CRASH_STOP,
IPI_TIMER,
IPI_IRQ_WORK,
- NR_IPI
+ NR_IPI,
+ /*
+ * Any enum >= NR_IPI and < MAX_IPI is special and not tracable
+ * with trace_ipi_*
+ */
+ IPI_CPU_BACKTRACE = NR_IPI,
+ MAX_IPI
};
static int ipi_irq_base __read_mostly;
static int nr_ipi __read_mostly = NR_IPI;
-static struct irq_desc *ipi_desc[NR_IPI] __read_mostly;
+static struct irq_desc *ipi_desc[MAX_IPI] __read_mostly;
static void ipi_setup(int cpu);
@@ -845,6 +852,22 @@ static void __noreturn ipi_cpu_crash_stop(unsigned int cpu, struct pt_regs *regs
#endif
}
+static void arm64_backtrace_ipi(cpumask_t *mask)
+{
+ __ipi_send_mask(ipi_desc[IPI_CPU_BACKTRACE], mask);
+}
+
+void arch_trigger_cpumask_backtrace(const cpumask_t *mask, int exclude_cpu)
+{
+ /*
+ * NOTE: though nmi_trigger_cpumask_backtrace has "nmi_" in the name,
+ * nothing about it truly needs to be implemented using an NMI, it's
+ * just that it's _allowed_ to work with NMIs. If ipi_should_be_nmi()
+ * returned false our backtrace attempt will just use a regular IPI.
+ */
+ nmi_trigger_cpumask_backtrace(mask, exclude_cpu, arm64_backtrace_ipi);
+}
+
/*
* Main handler for inter-processor interrupts
*/
@@ -888,6 +911,14 @@ static void do_handle_IPI(int ipinr)
break;
#endif
+ case IPI_CPU_BACKTRACE:
+ /*
+ * NOTE: in some cases this _won't_ be NMI context. See the
+ * comment in arch_trigger_cpumask_backtrace().
+ */
+ nmi_cpu_backtrace(get_irq_regs());
+ break;
+
default:
pr_crit("CPU%u: Unknown IPI message 0x%x\n", cpu, ipinr);
break;
@@ -909,6 +940,19 @@ static void smp_cross_call(const struct cpumask *target, unsigned int ipinr)
__ipi_send_mask(ipi_desc[ipinr], target);
}
+static bool ipi_should_be_nmi(enum ipi_msg_type ipi)
+{
+ if (!system_uses_irq_prio_masking())
+ return false;
+
+ switch (ipi) {
+ case IPI_CPU_BACKTRACE:
+ return true;
+ default:
+ return false;
+ }
+}
+
static void ipi_setup(int cpu)
{
int i;
@@ -916,8 +960,14 @@ static void ipi_setup(int cpu)
if (WARN_ON_ONCE(!ipi_irq_base))
return;
- for (i = 0; i < nr_ipi; i++)
- enable_percpu_irq(ipi_irq_base + i, 0);
+ for (i = 0; i < nr_ipi; i++) {
+ if (ipi_should_be_nmi(i)) {
+ prepare_percpu_nmi(ipi_irq_base + i);
+ enable_percpu_nmi(ipi_irq_base + i, 0);
+ } else {
+ enable_percpu_irq(ipi_irq_base + i, 0);
+ }
+ }
}
#ifdef CONFIG_HOTPLUG_CPU
@@ -928,8 +978,14 @@ static void ipi_teardown(int cpu)
if (WARN_ON_ONCE(!ipi_irq_base))
return;
- for (i = 0; i < nr_ipi; i++)
- disable_percpu_irq(ipi_irq_base + i);
+ for (i = 0; i < nr_ipi; i++) {
+ if (ipi_should_be_nmi(i)) {
+ disable_percpu_nmi(ipi_irq_base + i);
+ teardown_percpu_nmi(ipi_irq_base + i);
+ } else {
+ disable_percpu_irq(ipi_irq_base + i);
+ }
+ }
}
#endif
@@ -937,15 +993,23 @@ void __init set_smp_ipi_range(int ipi_base, int n)
{
int i;
- WARN_ON(n < NR_IPI);
- nr_ipi = min(n, NR_IPI);
+ WARN_ON(n < MAX_IPI);
+ nr_ipi = min(n, MAX_IPI);
for (i = 0; i < nr_ipi; i++) {
int err;
- err = request_percpu_irq(ipi_base + i, ipi_handler,
- "IPI", &cpu_number);
- WARN_ON(err);
+ if (ipi_should_be_nmi(i)) {
+ err = request_percpu_nmi(ipi_base + i, ipi_handler,
+ "IPI", &cpu_number);
+ WARN(err, "Could not request IPI %d as NMI, err=%d\n",
+ i, err);
+ } else {
+ err = request_percpu_irq(ipi_base + i, ipi_handler,
+ "IPI", &cpu_number);
+ WARN(err, "Could not request IPI %d as IRQ, err=%d\n",
+ i, err);
+ }
ipi_desc[i] = irq_to_desc(ipi_base + i);
irq_set_status_flags(ipi_base + i, IRQ_HIDDEN);
--
2.42.0.rc1.204.g551eb34607-goog
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