| Message ID | 20230601143109.v9.3.Ie6c132b96ebbbcddbf6954b9469ed40a6960343c@changeid (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: Add debug IPI for backtraces / kgdb; try to use NMI for it | expand |
On Thu, Jun 01, 2023 at 02:31:47PM -0700, Douglas Anderson wrote: > From: Sumit Garg <sumit.garg@linaro.org> > > Introduce a framework for an IPI that will be used for debug > purposes. The primary use case of this IPI will be to generate stack > crawls on other CPUs, but it will also be used to round up CPUs for > kgdb. > > When possible, we try to allocate this debug IPI as an NMI (or a > pseudo NMI). If that fails (due to CONFIG, an incompatible interrupt > controller, a quirk, missing the "irqchip.gicv3_pseudo_nmi=1" kernel > parameter, etc) we fall back to a normal IPI. > > NOTE: hooking this up for CPU backtrace / kgdb will happen in a future > patch, this just adds the framework. > > Signed-off-by: Sumit Garg <sumit.garg@linaro.org> > Signed-off-by: Douglas Anderson <dianders@chromium.org> I think that we shouldn't add a framework in a separate file for this: * This is very similar to our existing IPI management in smp.c, so it feels like duplication, or at least another thing we'd like to keep in-sync. * We're going to want an NMI backtrace regardless of KGDB * We're going to want the IPI_CPU_STOP and IPI_CRASH_CPU_STOP IPIs to be NMIs too. I reckon it'd be better to extend the existing IPI logic in smp.c to allow IPIs to be requested as NMIs, e.g. ---- diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index edd63894d61e8..48e6aa62c473e 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> @@ -926,6 +927,21 @@ 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) { + /* + * TODO: select NMI IPIs here + */ + return true; + default: + return false; + } +} + static void ipi_setup(int cpu) { int i; @@ -933,8 +949,14 @@ 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 @@ -945,8 +967,14 @@ 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 @@ -958,11 +986,19 @@ void __init set_smp_ipi_range(int ipi_base, int n) nr_ipi = min(n, NR_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); + int err = -EINVAL; + + 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); ---- ... and then if we need an IPI for KGDB, we can add that to the existing list of IPIs, and have it requested/enabled/disabled as usual. Thanks, Mark. > --- > I didn't get any feedback from v8 patch #10 [1], but I went ahead and > folded it in here anyway since it really simplfies things. If people > don't like the fallback to regular IPI, I can also undo it. > > [1] https://lore.kernel.org/r/20230419155341.v8.10.Ic3659997d6243139d0522fc3afcdfd88d7a5f030@changeid/ > > Changes in v9: > - 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. > > Changes in v8: > - debug_ipi_setup() and debug_ipi_teardown() no longer take cpu param > > arch/arm64/kernel/Makefile | 2 +- > arch/arm64/kernel/ipi_debug.c | 76 +++++++++++++++++++++++++++++++++++ > arch/arm64/kernel/ipi_debug.h | 13 ++++++ > 3 files changed, 90 insertions(+), 1 deletion(-) > create mode 100644 arch/arm64/kernel/ipi_debug.c > create mode 100644 arch/arm64/kernel/ipi_debug.h > > diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile > index cc22011ab66a..737838f803b7 100644 > --- a/arch/arm64/kernel/Makefile > +++ b/arch/arm64/kernel/Makefile > @@ -34,7 +34,7 @@ obj-y := debug-monitors.o entry.o irq.o fpsimd.o \ > cpufeature.o alternative.o cacheinfo.o \ > smp.o smp_spin_table.o topology.o smccc-call.o \ > syscall.o proton-pack.o idreg-override.o idle.o \ > - patching.o > + patching.o ipi_debug.o > > obj-$(CONFIG_COMPAT) += sys32.o signal32.o \ > sys_compat.o > diff --git a/arch/arm64/kernel/ipi_debug.c b/arch/arm64/kernel/ipi_debug.c > new file mode 100644 > index 000000000000..b57833e31eaf > --- /dev/null > +++ b/arch/arm64/kernel/ipi_debug.c > @@ -0,0 +1,76 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +/* > + * Debug IPI support > + * > + * Copyright (C) 2020 Linaro Limited > + * Author: Sumit Garg <sumit.garg@linaro.org> > + */ > + > +#include <linux/interrupt.h> > +#include <linux/irq.h> > +#include <linux/smp.h> > + > +#include "ipi_debug.h" > + > +static struct irq_desc *ipi_debug_desc __read_mostly; > +static int ipi_debug_id __read_mostly; > +static bool is_nmi; > + > +void arm64_debug_ipi(cpumask_t *mask) > +{ > + if (WARN_ON_ONCE(!ipi_debug_desc)) > + return; > + > + __ipi_send_mask(ipi_debug_desc, mask); > +} > + > +static irqreturn_t ipi_debug_handler(int irq, void *data) > +{ > + /* nop, NMI handlers for special features can be added here. */ > + > + return IRQ_NONE; > +} > + > +void debug_ipi_setup(void) > +{ > + if (!ipi_debug_desc) > + return; > + > + if (is_nmi) { > + if (!prepare_percpu_nmi(ipi_debug_id)) > + enable_percpu_nmi(ipi_debug_id, IRQ_TYPE_NONE); > + } else { > + enable_percpu_irq(ipi_debug_id, IRQ_TYPE_NONE); > + } > +} > + > +void debug_ipi_teardown(void) > +{ > + if (!ipi_debug_desc) > + return; > + > + if (is_nmi) { > + disable_percpu_nmi(ipi_debug_id); > + teardown_percpu_nmi(ipi_debug_id); > + } else { > + disable_percpu_irq(ipi_debug_id); > + } > +} > + > +void __init set_smp_debug_ipi(int ipi) > +{ > + int err; > + > + if (!request_percpu_nmi(ipi, ipi_debug_handler, "IPI", &cpu_number)) { > + is_nmi = true; > + } else { > + err = request_percpu_irq(ipi, ipi_debug_handler, "IPI", &cpu_number); > + if (WARN_ON(err)) > + return; > + > + irq_set_status_flags(ipi, IRQ_HIDDEN); > + } > + > + ipi_debug_desc = irq_to_desc(ipi); > + ipi_debug_id = ipi; > +} > diff --git a/arch/arm64/kernel/ipi_debug.h b/arch/arm64/kernel/ipi_debug.h > new file mode 100644 > index 000000000000..f6011a09282f > --- /dev/null > +++ b/arch/arm64/kernel/ipi_debug.h > @@ -0,0 +1,13 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef __ASM_NMI_H > +#define __ASM_NMI_H > + > +#include <linux/cpumask.h> > + > +void arm64_debug_ipi(cpumask_t *mask); > + > +void set_smp_debug_ipi(int ipi); > +void debug_ipi_setup(void); > +void debug_ipi_teardown(void); > + > +#endif > -- > 2.41.0.rc2.161.g9c6817b8e7-goog >
Hi, On Mon, Aug 7, 2023 at 3:12 AM Mark Rutland <mark.rutland@arm.com> wrote: > > On Thu, Jun 01, 2023 at 02:31:47PM -0700, Douglas Anderson wrote: > > From: Sumit Garg <sumit.garg@linaro.org> > > > > Introduce a framework for an IPI that will be used for debug > > purposes. The primary use case of this IPI will be to generate stack > > crawls on other CPUs, but it will also be used to round up CPUs for > > kgdb. > > > > When possible, we try to allocate this debug IPI as an NMI (or a > > pseudo NMI). If that fails (due to CONFIG, an incompatible interrupt > > controller, a quirk, missing the "irqchip.gicv3_pseudo_nmi=1" kernel > > parameter, etc) we fall back to a normal IPI. > > > > NOTE: hooking this up for CPU backtrace / kgdb will happen in a future > > patch, this just adds the framework. > > > > Signed-off-by: Sumit Garg <sumit.garg@linaro.org> > > Signed-off-by: Douglas Anderson <dianders@chromium.org> > > I think that we shouldn't add a framework in a separate file for this: > > * This is very similar to our existing IPI management in smp.c, so it feels > like duplication, or at least another thing we'd like to keep in-sync. > > * We're going to want an NMI backtrace regardless of KGDB > > * We're going to want the IPI_CPU_STOP and IPI_CRASH_CPU_STOP IPIs to be NMIs > too. > > I reckon it'd be better to extend the existing IPI logic in smp.c to allow IPIs > to be requested as NMIs, e.g. > > ---- > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c > index edd63894d61e8..48e6aa62c473e 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> > @@ -926,6 +927,21 @@ 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) { > + /* > + * TODO: select NMI IPIs here > + */ > + return true; > + default: > + return false; > + } > +} > + > static void ipi_setup(int cpu) > { > int i; > @@ -933,8 +949,14 @@ 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 > @@ -945,8 +967,14 @@ 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 > > @@ -958,11 +986,19 @@ void __init set_smp_ipi_range(int ipi_base, int n) > nr_ipi = min(n, NR_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); > + int err = -EINVAL; > + > + 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); > ---- > > ... and then if we need an IPI for KGDB, we can add that to the existing list > of IPIs, and have it requested/enabled/disabled as usual. Sounds good. I'm starting to work on v10 incorporating your feedback. A few quick questions: 1. If I mostly take your patch above verbatim, do you have any suggested tags for Author/Signed-off-by? I'd tend to set you as the author but I can't do that because you didn't provide a Signed-off-by... 2. Would you prefer this patch on its own, or would you rather it be squashed with the first user ("backtrace")? On its own, I think I have to get rid of the "switch" statement in ipi_should_be_nmi() and just return false; Thanks! -Doug
On Mon, Aug 21, 2023 at 03:16:56PM -0700, Doug Anderson wrote: > Hi, > > On Mon, Aug 7, 2023 at 3:12 AM Mark Rutland <mark.rutland@arm.com> wrote: > > > > On Thu, Jun 01, 2023 at 02:31:47PM -0700, Douglas Anderson wrote: > > > From: Sumit Garg <sumit.garg@linaro.org> > > > > > > Introduce a framework for an IPI that will be used for debug > > > purposes. The primary use case of this IPI will be to generate stack > > > crawls on other CPUs, but it will also be used to round up CPUs for > > > kgdb. > > > > > > When possible, we try to allocate this debug IPI as an NMI (or a > > > pseudo NMI). If that fails (due to CONFIG, an incompatible interrupt > > > controller, a quirk, missing the "irqchip.gicv3_pseudo_nmi=1" kernel > > > parameter, etc) we fall back to a normal IPI. > > > > > > NOTE: hooking this up for CPU backtrace / kgdb will happen in a future > > > patch, this just adds the framework. > > > > > > Signed-off-by: Sumit Garg <sumit.garg@linaro.org> > > > Signed-off-by: Douglas Anderson <dianders@chromium.org> > > > > I think that we shouldn't add a framework in a separate file for this: > > > > * This is very similar to our existing IPI management in smp.c, so it feels > > like duplication, or at least another thing we'd like to keep in-sync. > > > > * We're going to want an NMI backtrace regardless of KGDB > > > > * We're going to want the IPI_CPU_STOP and IPI_CRASH_CPU_STOP IPIs to be NMIs > > too. > > > > I reckon it'd be better to extend the existing IPI logic in smp.c to allow IPIs > > to be requested as NMIs, e.g. > > > > ---- > > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c > > index edd63894d61e8..48e6aa62c473e 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> > > @@ -926,6 +927,21 @@ 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) { > > + /* > > + * TODO: select NMI IPIs here > > + */ > > + return true; > > + default: > > + return false; > > + } > > +} > > + > > static void ipi_setup(int cpu) > > { > > int i; > > @@ -933,8 +949,14 @@ 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 > > @@ -945,8 +967,14 @@ 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 > > > > @@ -958,11 +986,19 @@ void __init set_smp_ipi_range(int ipi_base, int n) > > nr_ipi = min(n, NR_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); > > + int err = -EINVAL; > > + > > + 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); > > ---- > > > > ... and then if we need an IPI for KGDB, we can add that to the existing list > > of IPIs, and have it requested/enabled/disabled as usual. > > Sounds good. I'm starting to work on v10 incorporating your feedback. > A few quick questions: > > 1. If I mostly take your patch above verbatim, do you have any > suggested tags for Author/Signed-off-by? I'd tend to set you as the > author but I can't do that because you didn't provide a > Signed-off-by... Sorry about that. For the above: Signed-off-by: Mark Rutland <mark.rutland@arm.com> If squashed into another patch, then feel free to use: Co-developed-by: Mark Rutland <mark.rutland@arm.com> > 2. Would you prefer this patch on its own, or would you rather it be > squashed with the first user ("backtrace")? On its own, I think I have > to get rid of the "switch" statement in ipi_should_be_nmi() and just > return false; I reckon it makes sense to squash it with the first user. Thanks, Mark.
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index cc22011ab66a..737838f803b7 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -34,7 +34,7 @@ obj-y := debug-monitors.o entry.o irq.o fpsimd.o \ cpufeature.o alternative.o cacheinfo.o \ smp.o smp_spin_table.o topology.o smccc-call.o \ syscall.o proton-pack.o idreg-override.o idle.o \ - patching.o + patching.o ipi_debug.o obj-$(CONFIG_COMPAT) += sys32.o signal32.o \ sys_compat.o diff --git a/arch/arm64/kernel/ipi_debug.c b/arch/arm64/kernel/ipi_debug.c new file mode 100644 index 000000000000..b57833e31eaf --- /dev/null +++ b/arch/arm64/kernel/ipi_debug.c @@ -0,0 +1,76 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Debug IPI support + * + * Copyright (C) 2020 Linaro Limited + * Author: Sumit Garg <sumit.garg@linaro.org> + */ + +#include <linux/interrupt.h> +#include <linux/irq.h> +#include <linux/smp.h> + +#include "ipi_debug.h" + +static struct irq_desc *ipi_debug_desc __read_mostly; +static int ipi_debug_id __read_mostly; +static bool is_nmi; + +void arm64_debug_ipi(cpumask_t *mask) +{ + if (WARN_ON_ONCE(!ipi_debug_desc)) + return; + + __ipi_send_mask(ipi_debug_desc, mask); +} + +static irqreturn_t ipi_debug_handler(int irq, void *data) +{ + /* nop, NMI handlers for special features can be added here. */ + + return IRQ_NONE; +} + +void debug_ipi_setup(void) +{ + if (!ipi_debug_desc) + return; + + if (is_nmi) { + if (!prepare_percpu_nmi(ipi_debug_id)) + enable_percpu_nmi(ipi_debug_id, IRQ_TYPE_NONE); + } else { + enable_percpu_irq(ipi_debug_id, IRQ_TYPE_NONE); + } +} + +void debug_ipi_teardown(void) +{ + if (!ipi_debug_desc) + return; + + if (is_nmi) { + disable_percpu_nmi(ipi_debug_id); + teardown_percpu_nmi(ipi_debug_id); + } else { + disable_percpu_irq(ipi_debug_id); + } +} + +void __init set_smp_debug_ipi(int ipi) +{ + int err; + + if (!request_percpu_nmi(ipi, ipi_debug_handler, "IPI", &cpu_number)) { + is_nmi = true; + } else { + err = request_percpu_irq(ipi, ipi_debug_handler, "IPI", &cpu_number); + if (WARN_ON(err)) + return; + + irq_set_status_flags(ipi, IRQ_HIDDEN); + } + + ipi_debug_desc = irq_to_desc(ipi); + ipi_debug_id = ipi; +} diff --git a/arch/arm64/kernel/ipi_debug.h b/arch/arm64/kernel/ipi_debug.h new file mode 100644 index 000000000000..f6011a09282f --- /dev/null +++ b/arch/arm64/kernel/ipi_debug.h @@ -0,0 +1,13 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __ASM_NMI_H +#define __ASM_NMI_H + +#include <linux/cpumask.h> + +void arm64_debug_ipi(cpumask_t *mask); + +void set_smp_debug_ipi(int ipi); +void debug_ipi_setup(void); +void debug_ipi_teardown(void); + +#endif