[RFC PATCH v2 39/45] arm64: smp: Fall back to IRQ when IPI NMI request fails
From: Vladimir Murzin <hidden>
Date: 2026-07-27 17:21:29
Subsystem:
arm64 port (aarch64 architecture), the rest · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds
Existing IPI setup logic relies on ipi_should_be_nmi() to decide whether to request an NMI (if supported) or an ordinary IRQ. If NMI is not supported, using an ordinary IRQ is acceptable. FEAT_NMI requires complementary support in the interrupt controller. If FEAT_NMI is present but interrupt controller support is absent, request_percpu_nmi() can fail. One way to prevent this would be to extend ipi_should_be_nmi() to also check for interrupt controller support. However, since falling back to an ordinary IRQ is acceptable, treat ipi_should_be_nmi() as a hint instead. Whether an IPI is actually registered as an NMI is determined by the success or failure of request_percpu_nmi(). If the request fails, fall back to request_irq(). Track which IPIs were actually registered as NMIs and use that state in the per-CPU enable and disable paths. This avoids calling the percpu NMI helpers for an IPI that fell back to regular IRQ handling. Signed-off-by: Vladimir Murzin <redacted> --- arch/arm64/kernel/smp.c | 31 +++++++++++++++++++++++-------- 1 file changed, 23 insertions(+), 8 deletions(-)
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 3dd4bc02caed..9bacdbb2aa44 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c@@ -69,11 +69,13 @@ static int nr_ipi __ro_after_init = NR_IPI; struct ipi_descs { struct irq_desc *descs[MAX_IPI]; + DECLARE_BITMAP(nmi_bitmap, MAX_IPI); }; static DEFINE_PER_CPU_READ_MOSTLY(struct ipi_descs, pcpu_ipi_desc); #define get_ipi_desc(__cpu, __ipi) (per_cpu_ptr(&pcpu_ipi_desc, __cpu)->descs[__ipi]) +#define get_ipi_nmi_bitmap(__cpu) (per_cpu_ptr(&pcpu_ipi_desc, __cpu)->nmi_bitmap) struct ipi_irq_ops { void (*setup)(int ipi, int ncpus);
@@ -1051,31 +1053,44 @@ static bool ipi_should_be_nmi(enum ipi_msg_type ipi) static void ipi_sgi_setup(int ipi, int ncpus) { + bool is_nmi = ipi_should_be_nmi(ipi); int err, irq, cpu; if (WARN_ON_ONCE(ncpus)) return; - irq = ipi_irq_base + ipi; - if (ipi_should_be_nmi(ipi)) { - err = request_percpu_nmi(irq, ipi_handler, "IPI", NULL, &irq_stat); - WARN(err, "Could not request IRQ %d as NMI, err=%d\n", irq, err); - } else { + /* + * Try to request NMI if it should be + */ + if (is_nmi && request_percpu_nmi(irq, ipi_handler, "IPI", NULL, &irq_stat)) { + /* + * Fallback to regular IRQ + */ + is_nmi = false; + } + + /* + * Otherwise regular IRQ + */ + if (!is_nmi) { err = request_percpu_irq(irq, ipi_handler, "IPI", &irq_stat); WARN(err, "Could not request IRQ %d as IRQ, err=%d\n", irq, err); } - for_each_possible_cpu(cpu) + for_each_possible_cpu(cpu) { get_ipi_desc(cpu, ipi) = irq_to_desc(irq); + if (is_nmi) + set_bit(ipi, get_ipi_nmi_bitmap(cpu)); + } irq_set_status_flags(irq, IRQ_HIDDEN); } static void ipi_sgi_enable(int cpu, int ipi) { - if (ipi_should_be_nmi(ipi)) { + if (test_bit(ipi, get_ipi_nmi_bitmap(cpu))) { prepare_percpu_nmi(ipi_irq_base + ipi); enable_percpu_nmi(ipi_irq_base + ipi, 0); } else {
@@ -1085,7 +1100,7 @@ static void ipi_sgi_enable(int cpu, int ipi) static void ipi_sgi_disable(int cpu, int ipi) { - if (ipi_should_be_nmi(ipi)) { + if (test_bit(ipi, get_ipi_nmi_bitmap(cpu))) { disable_percpu_nmi(ipi_irq_base + ipi); teardown_percpu_nmi(ipi_irq_base + ipi); } else {
--
2.34.1