also to round up CPUs in kdb/kgdb. The last post from Sumit that I

could find was v7, so I started my series at v8. I haven't copied all

of his old changelongs here, but you can find them from the link.

This patch series targets v6.6. Specifically it can't land in v6.5

excluding an arbitrary CPU").

It should be noted that Mark still feels there might be some corner

cases where pseudo-NMI is not production ready [2] [3], but as far as

I'm aware there are no concrete/documented issues. Regardless of

whether this should be enabled for production, though, this series

will be invaluable to anyone trying to debug crashes on arm64

machines.

v9. As a quick summary:

- It includes his patch to remove IPI_WAKEUP, freeing up an extra IPI.

- It no longer combines the "kgdb" and "backtrace" IPIs. If we need

another IPI these could always be recombined later.

- It promotes IPI_CPU_STOP and IPI_CPU_CRASH_STOP to NMI.

* Added an extra patch to gracefully fall back to regular IPIs if

pseudo-NMIs aren't there.

It can be noted that this patch series works very well with the recent

"hardlockup" patches that have landed through Andrew Morton's tree and

lockup detector.

[1] https://lore.kernel.org/linux-arm-kernel/1604317487-14543-1-git-send-email-sumit.garg@linaro.org/

[2] https://lore.kernel.org/lkml/ZFvGqD%2F%2Fpm%2FlZb+p@FVFF77S0Q05N.cambridge.arm.com/

[3] https://lore.kernel.org/lkml/ZNDKVP2m-iiZCz3v@FVFF77S0Q05N.cambridge.arm.com

[4] https://lore.kernel.org/r/20230419155341.v8.10.Ic3659997d6243139d0522fc3afcdfd88d7a5f030@changeid/

Changes in v10:

- ("IPI_CPU_STOP and IPI_CPU_CRASH_STOP should try for NMI") new for v10.

- ("arm64: smp: Remove dedicated wakeup IPI") new for v10.

- Backtrace now directly supported in smp.c

Changes in v8:

- "Tag the arm64 idle functions as __cpuidle" new for v8

- Removed "#ifdef CONFIG_SMP" since arm64 is always SMP

- debug_ipi_setup() and debug_ipi_teardown() no longer take cpu param

irqchip/gic-v3: Enable support for SGIs to act as NMIs

arm64: idle: Tag the arm64 idle functions as __cpuidle

arm64: smp: Add arch support for backtrace using pseudo-NMI

arm64: smp: IPI_CPU_STOP and IPI_CPU_CRASH_STOP should try for NMI

arm64: kgdb: Implement kgdb_roundup_cpus() to enable pseudo-NMI

roundup

Mark Rutland (1):

arm64: smp: Remove dedicated wakeup IPI

arch/arm64/include/asm/irq.h | 3 +

arch/arm64/include/asm/smp.h | 4 +-

arch/arm64/kernel/acpi_parking_protocol.c | 2 +-

arch/arm64/kernel/idle.c | 4 +-

--

Co-developed-by: Sumit Garg <sumit.garg@linaro.org>

Signed-off-by: Sumit Garg <sumit.garg@linaro.org>

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

---

Mark's advice wasn't a full patch and I ended up doing a bit of work

to translate it to reality, so I did not add him as "Co-developed-by"

here. Mark: if you would like this tag then please provide it and your

Signed-off-by. I certainly won't object.

[1] https://lore.kernel.org/r/ZNC-YRQopO0PaIIo@FVFF77S0Q05N.cambridge.arm.com

Changes in v10:

- Rewrite as needed for 5.11+ as per Mark Rutland and Sumit.

diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c

index XXXXXXX..XXXXXXX 100644

--- a/drivers/irqchip/irq-gic-v3.c

+++ b/drivers/irqchip/irq-gic-v3.c

@@ -XXX,XX +XXX,XX @@ static DEFINE_STATIC_KEY_TRUE(supports_deactivate_key);

#define GIC_LINE_NR    min(GICD_TYPER_SPIS(gic_data.rdists.gicd_typer), 1020U)

#define GIC_ESPI_NR    GICD_TYPER_ESPIS(gic_data.rdists.gicd_typer)

+#define SGI_NR        16

+

/*

* The behaviours of RPR and PMR registers differ depending on the value of

* SCR_EL3.FIQ, and the behaviour of non-secure priority registers of the

-

    return 0;

out_free:

--

As per the (somewhat recent) comment before the definition of

`__cpuidle`, the tag is like `noinstr` but also marks a function so it

NMI backtrace for cpu N skipped: idling at cpu_do_idle+0x94/0x98

NOTE: this patch won't make cpu_in_idle() work perfectly for arm64,

but it doesn't hurt and does catch some cases. Specifically an example

that wasn't caught in my testing looked like this:

cpuidle_enter_state+0xb8/0x260

cpuidle_enter+0x44/0x5c

do_idle+0x188/0x30c

Acked-by: Mark Rutland <mark.rutland@arm.com>

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

---

Changes in v9:

- Added to commit message that this doesn't catch all cases.

Changes in v8:

+void __cpuidle arch_cpu_idle(void)

{

    /*

     * This should do all the clock switching and wait for interrupt

--

cost of taking and handling the IPI in the first place. We can safely

handle redundant IPI_RESCHEDULE IPIs, so there should be no functional

impact as a result of this change.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>

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

Cc: Catalin Marinas <catalin.marinas@arm.com>

Cc: Marc Zyngier <maz@kernel.org>

Cc: Will Deacon <will@kernel.org>

---

I have no idea how to test this. I just took Mark's patch and jammed

it into my series. Logicially the patch seems reasonable to me.

Changes in v10:

- ("arm64: smp: Remove dedicated wakeup IPI") new for v10.

arch/arm64/include/asm/smp.h | 4 ++--

@@ -XXX,XX +XXX,XX @@ extern void arch_send_call_function_single_ipi(int cpu);

extern void arch_send_call_function_ipi_mask(const struct cpumask *mask);

#ifdef CONFIG_ARM64_ACPI_PARKING_PROTOCOL

-extern void arch_send_wakeup_ipi_mask(const struct cpumask *mask);

#else

-static inline void arch_send_wakeup_ipi_mask(const struct cpumask *mask)

{

    BUILD_BUG();

}

diff --git a/arch/arm64/kernel/acpi_parking_protocol.c b/arch/arm64/kernel/acpi_parking_protocol.c

index XXXXXXX..XXXXXXX 100644

@@ -XXX,XX +XXX,XX @@ void arch_smp_send_reschedule(int cpu)

    smp_cross_call(cpumask_of(cpu), IPI_RESCHEDULE);

}

+#ifdef CONFIG_ARM64_ACPI_PARKING_PROTOCOL

+{

+    /*

+     * We use a scheduler IPI to wake the CPU as this avoids the need for a

+     * dedicated IPI and we can safely handle spurious scheduler IPIs.

+     */

+

#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST

void tick_broadcast(const struct cpumask *mask)

{

--

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].

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@linaro.org>

Signed-off-by: Sumit Garg <sumit.garg@linaro.org>

Co-developed-by: Mark Rutland <mark.rutland@arm.com>

Signed-off-by: Mark Rutland <mark.rutland@arm.com>

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

---

Changes in v10:

- Backtrace now directly supported in smp.c

- Squash backtrace into patch adding support for pseudo-NMI IPIs.

    IPI_TIMER,

    IPI_IRQ_WORK,

-    NR_IPI

+    NR_IPI,

+    /*

+     */

+    IPI_CPU_BACKTRACE = NR_IPI,

+    MAX_IPI

};

@@ -XXX,XX +XXX,XX @@ static void __noreturn ipi_cpu_crash_stop(unsigned int cpu, struct pt_regs *regs

#endif

}

+{

+    __ipi_send_mask(ipi_desc[IPI_CPU_BACKTRACE], mask);

+}

+

+void arch_trigger_cpumask_backtrace(const cpumask_t *mask, int exclude_cpu)

+{

+    /*

+     */

+    nmi_trigger_cpumask_backtrace(mask, exclude_cpu, arm64_backtrace_ipi);

+}

+

/*

+        }

        ipi_desc[i] = irq_to_desc(ipi_base + i);

        irq_set_status_flags(ipi_base + i, IRQ_HIDDEN);

--

There's no reason why IPI_CPU_STOP and IPI_CPU_CRASH_STOP can't be

handled as NMI. They are very simple and everything in them is

NMI-safe. Mark them as things to use NMI for if NMI is available.

Suggested-by: Mark Rutland <mark.rutland@arm.com>

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

---

I don't actually have any good way to test/validate this patch. It's

added to the series at Mark's request.

Changes in v10:

- ("IPI_CPU_STOP and IPI_CPU_CRASH_STOP should try for NMI") new for v10.

arch/arm64/kernel/smp.c | 2 ++

+    case IPI_CPU_CRASH_STOP:

    case IPI_CPU_BACKTRACE:

        return true;

    default:

--

it avoids the potential situation described in the generic

kgdb_call_nmi_hook().

Co-developed-by: Sumit Garg <sumit.garg@linaro.org>

Signed-off-by: Sumit Garg <sumit.garg@linaro.org>

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

---

I debated whether this should be in "arch/arm64/kernel/smp.c" or if I

should try to find a way for it to go into "arch/arm64/kernel/kgdb.c".

In the end this is so little code that it didn't seem worth it to find

FWIW, it seems like ~half the other platforms put this in "smp.c" with

an ifdef for KGDB and the other half put it in "kgdb.c" with an ifdef

for SMP. :-P

Changes in v10:

- Don't allocate the cpumask on the stack; just iterate.

- Moved kgdb calls to smp.c to avoid needing to export IPI info.

- kgdb now has its own IPI.

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.

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c

index XXXXXXX..XXXXXXX 100644

--- a/arch/arm64/kernel/smp.c

+++ b/arch/arm64/kernel/smp.c

+#include <linux/kgdb.h>

#include <linux/kvm_host.h>

#include <linux/nmi.h>

@@ -XXX,XX +XXX,XX @@ enum ipi_msg_type {

     */

    IPI_CPU_BACKTRACE = NR_IPI,

+    IPI_KGDB_ROUNDUP,

    MAX_IPI

};

+    case IPI_KGDB_ROUNDUP:

        return true;

    default:

        return false;

--