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Subject[PATCH v5 25/27] irqchip/gic-v3: Add base support for pseudo-NMI
Date
Provide a higher priority to be used for pseudo-NMIs. When such an
interrupt is received, enter the NMI state and prevent other NMIs to
be raised.

When returning from a pseudo-NMI, skip preemption and tracing if the
interrupted context has interrupts disabled.

Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Marc Zyngier <marc.zyngier@arm.com>
---
arch/arm/include/asm/arch_gicv3.h | 6 ++++++
arch/arm64/include/asm/arch_gicv3.h | 6 ++++++
arch/arm64/kernel/entry.S | 43 +++++++++++++++++++++++++++++++++++++
drivers/irqchip/irq-gic-v3.c | 34 ++++++++++++++++++++++++++++-
4 files changed, 88 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/arch_gicv3.h b/arch/arm/include/asm/arch_gicv3.h
index b39d620..1ed0476 100644
--- a/arch/arm/include/asm/arch_gicv3.h
+++ b/arch/arm/include/asm/arch_gicv3.h
@@ -374,5 +374,11 @@ static inline void gic_start_pmr_masking(void)
WARN_ON(true);
}

+static inline void gic_set_nmi_active(void)
+{
+ /* Should not get called */
+ WARN_ON(true);
+}
+
#endif /* !__ASSEMBLY__ */
#endif /* !__ASM_ARCH_GICV3_H */
diff --git a/arch/arm64/include/asm/arch_gicv3.h b/arch/arm64/include/asm/arch_gicv3.h
index eb55da8..6213d6f 100644
--- a/arch/arm64/include/asm/arch_gicv3.h
+++ b/arch/arm64/include/asm/arch_gicv3.h
@@ -167,5 +167,11 @@ static inline void gic_start_pmr_masking(void)
asm volatile ("msr daifclr, #2" : : : "memory");
}

+/* Notify an NMI is active, blocking other NMIs */
+static inline void gic_set_nmi_active(void)
+{
+ asm volatile ("msr daifset, #2" : : : "memory");
+}
+
#endif /* __ASSEMBLY__ */
#endif /* __ASM_ARCH_GICV3_H */
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 91e1e3d..39d6ef0 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -411,6 +411,16 @@ alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0
mov sp, x19
.endm

+ /* Should be checked on return from irq handlers */
+ .macro branch_if_was_nmi, tmp, target
+ alternative_if ARM64_HAS_IRQ_PRIO_MASKING
+ mrs \tmp, daif
+ alternative_else
+ mov \tmp, #0
+ alternative_endif
+ tbnz \tmp, #7, \target // Exiting an NMI
+ .endm
+
/*
* These are the registers used in the syscall handler, and allow us to
* have in theory up to 7 arguments to a function - x0 to x6.
@@ -631,12 +641,30 @@ ENDPROC(el1_sync)
el1_irq:
kernel_entry 1
enable_da_f
+
#ifdef CONFIG_TRACE_IRQFLAGS
+#ifdef CONFIG_USE_ICC_SYSREGS_FOR_IRQFLAGS
+ ldr x20, [sp, #S_PMR_SAVE]
+ /* Irqs were disabled, don't trace */
+ tbz x20, ICC_PMR_EL1_EN_SHIFT, 1f
+#endif
bl trace_hardirqs_off
+1:
#endif

irq_handler

+#ifdef CONFIG_USE_ICC_SYSREGS_FOR_IRQFLAGS
+ /*
+ * Irqs were disabled, we have an nmi.
+ * We might have interrupted a context with interrupt disabled that set
+ * NEED_RESCHED flag.
+ * Skip preemption and irq tracing if needed.
+ */
+ tbz x20, ICC_PMR_EL1_EN_SHIFT, untraced_irq_exit
+ branch_if_was_nmi x0, skip_preempt
+#endif
+
#ifdef CONFIG_PREEMPT
ldr w24, [tsk, #TSK_TI_PREEMPT] // get preempt count
cbnz w24, 1f // preempt count != 0
@@ -645,9 +673,13 @@ el1_irq:
bl el1_preempt
1:
#endif
+
+skip_preempt:
#ifdef CONFIG_TRACE_IRQFLAGS
bl trace_hardirqs_on
#endif
+
+untraced_irq_exit:
kernel_exit 1
ENDPROC(el1_irq)

@@ -873,6 +905,9 @@ el0_irq_naked:
#ifdef CONFIG_TRACE_IRQFLAGS
bl trace_hardirqs_on
#endif
+
+ branch_if_was_nmi x2, nmi_ret_to_user
+
b ret_to_user
ENDPROC(el0_irq)

@@ -1269,3 +1304,11 @@ alternative_else_nop_endif
ENDPROC(__sdei_asm_handler)
NOKPROBE(__sdei_asm_handler)
#endif /* CONFIG_ARM_SDE_INTERFACE */
+
+/*
+ * NMI return path to EL0
+ */
+nmi_ret_to_user:
+ ldr x1, [tsk, #TSK_TI_FLAGS]
+ b finish_ret_to_user
+ENDPROC(nmi_ret_to_user)
diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index ffe98e8..1af2fcc 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -41,6 +41,8 @@

#include "irq-gic-common.h"

+#define GICD_INT_NMI_PRI 0xa0
+
struct redist_region {
void __iomem *redist_base;
phys_addr_t phys_base;
@@ -248,6 +250,12 @@ static void gic_unmask_irq(struct irq_data *d)
gic_poke_irq(d, GICD_ISENABLER);
}

+static inline bool gic_supports_nmi(void)
+{
+ return gic_prio_masking_enabled()
+ && static_branch_likely(&have_non_secure_prio_view);
+}
+
static int gic_irq_set_irqchip_state(struct irq_data *d,
enum irqchip_irq_state which, bool val)
{
@@ -381,6 +389,23 @@ static asmlinkage void __exception_irq_entry gic_handle_irq(struct pt_regs *regs
if (likely(irqnr > 15 && irqnr < 1020) || irqnr >= 8192) {
int err;

+ if (gic_supports_nmi()
+ && unlikely(gic_read_rpr() == GICD_INT_NMI_PRI)) {
+ /*
+ * We need to prevent other NMIs to occur even after a
+ * priority drop.
+ * We keep I flag set until cpsr is restored from
+ * kernel_exit.
+ */
+ gic_set_nmi_active();
+
+ if (static_branch_likely(&supports_deactivate_key))
+ gic_write_eoir(irqnr);
+
+ err = handle_domain_nmi(gic_data.domain, irqnr, regs);
+ return;
+ }
+
if (static_branch_likely(&supports_deactivate_key))
gic_write_eoir(irqnr);
else if (!gic_prio_masking_enabled())
@@ -1119,6 +1144,11 @@ static int partition_domain_translate(struct irq_domain *d,
.select = gic_irq_domain_select,
};

+static void gic_enable_nmi_support(void)
+{
+ static_branch_enable(&have_non_secure_prio_view);
+}
+
static int __init gic_init_bases(void __iomem *dist_base,
struct redist_region *rdist_regs,
u32 nr_redist_regions,
@@ -1188,7 +1218,9 @@ static int __init gic_init_bases(void __iomem *dist_base,

if (gic_prio_masking_enabled()) {
if (!gic_has_group0() || gic_dist_security_disabled())
- static_branch_enable(&have_non_secure_prio_view);
+ gic_enable_nmi_support();
+ else
+ pr_warn("SCR_EL3.FIQ set, cannot enable use of pseudo-NMIs\n");
}

return 0;
--
1.9.1
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