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Message-Id: <1442237181-17064-7-git-send-email-daniel.thompson@linaro.org>
Date: Mon, 14 Sep 2015 14:26:20 +0100
From: Daniel Thompson <daniel.thompson@...aro.org>
To: linux-arm-kernel@...ts.infradead.org
Cc: Daniel Thompson <daniel.thompson@...aro.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
linux-kernel@...r.kernel.org, patches@...aro.org,
linaro-kernel@...ts.linaro.org,
John Stultz <john.stultz@...aro.org>,
Sumit Semwal <sumit.semwal@...aro.org>,
Marc Zyngier <marc.zyngier@....com>,
Andrew Thoelke <andrew.thoelke@....com>,
Dave Martin <dave.martin@....com>
Subject: [RFC PATCH v2 6/7] arm64: Implement IPI_CPU_BACKTRACE using pseudo-NMIs
Recently arm64 gained the capability to (optionally) mask interrupts
using the GIC PMR rather than the CPU PSR. That allows us to introduce
an NMI-like means to handle backtrace requests.
This provides a useful debug aid by allowing the kernel to robustly show
a backtrace for every processor in the system when, for example, we hang
trying to acquire a spin lock.
Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
---
arch/arm64/include/asm/assembler.h | 23 +++++++++++
arch/arm64/include/asm/smp.h | 2 +
arch/arm64/kernel/entry.S | 78 ++++++++++++++++++++++++++++++--------
arch/arm64/kernel/smp.c | 20 +++++++++-
drivers/irqchip/irq-gic-v3.c | 69 +++++++++++++++++++++++++++++++++
5 files changed, 176 insertions(+), 16 deletions(-)
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index ab7c3ffd6104..da6b8d9913de 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -42,6 +42,29 @@
.endm
/*
+ * Enable and disable pseudo NMI.
+ */
+ .macro disable_nmi
+#ifdef CONFIG_USE_ICC_SYSREGS_FOR_IRQFLAGS
+alternative_if_not ARM64_HAS_SYSREG_GIC_CPUIF
+ nop
+alternative_else
+ msr daifset, #2
+alternative_endif
+#endif
+ .endm
+
+ .macro enable_nmi
+#ifdef CONFIG_USE_ICC_SYSREGS_FOR_IRQFLAGS
+alternative_if_not ARM64_HAS_SYSREG_GIC_CPUIF
+ nop
+alternative_else
+ msr daifclr, #2
+alternative_endif
+#endif
+ .endm
+
+/*
* Enable and disable interrupts.
*/
.macro disable_irq, tmp
diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h
index d9c3d6a6100a..fc310b6486b1 100644
--- a/arch/arm64/include/asm/smp.h
+++ b/arch/arm64/include/asm/smp.h
@@ -20,6 +20,8 @@
#include <linux/cpumask.h>
#include <linux/thread_info.h>
+#define SMP_IPI_NMI_MASK (1 << 5)
+
#define raw_smp_processor_id() (current_thread_info()->cpu)
struct seq_file;
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index ccbe867c7734..2f4d69f62138 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -205,6 +205,40 @@ alternative_endif
and \rd, \rd, #~(THREAD_SIZE - 1) // top of stack
.endm
+ .macro trace_hardirqs_off, pstate
+#ifdef CONFIG_TRACE_IRQFLAGS
+#ifdef CONFIG_USE_ICC_SYSREGS_FOR_IRQFLAGS
+alternative_if_not ARM64_HAS_SYSREG_GIC_CPUIF
+ bl trace_hardirqs_off
+ nop
+alternative_else
+ tbnz \pstate, #PSR_G_SHIFT, 1f // PSR_G_BIT
+ bl trace_hardirqs_off
+1:
+alternative_endif
+#else
+ bl trace_hardirqs_off
+#endif
+#endif
+ .endm
+
+ .macro trace_hardirqs_on, pstate
+#ifdef CONFIG_TRACE_IRQFLAGS
+#ifdef CONFIG_USE_ICC_SYSREGS_FOR_IRQFLAGS
+alternative_if_not ARM64_HAS_SYSREG_GIC_CPUIF
+ bl trace_hardirqs_on
+ nop
+alternative_else
+ tbnz \pstate, #PSR_G_SHIFT, 1f // PSR_G_BIT
+ bl trace_hardirqs_on
+1:
+alternative_endif
+#else
+ bl trace_hardirqs_on
+#endif
+#endif
+ .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.
@@ -341,20 +375,19 @@ el1_da:
* Data abort handling
*/
mrs x0, far_el1
+ enable_nmi
enable_dbg
// re-enable interrupts if they were enabled in the aborted context
#ifdef CONFIG_USE_ICC_SYSREGS_FOR_IRQFLAGS
alternative_if_not ARM64_HAS_SYSREG_GIC_CPUIF
tbnz x23, #7, 1f // PSR_I_BIT
nop
- nop
msr daifclr, #2
1:
alternative_else
tbnz x23, #PSR_G_SHIFT, 1f // PSR_G_BIT
mov x2, #ICC_PMR_EL1_UNMASKED
msr_s ICC_PMR_EL1, x2
- msr daifclr, #2
1:
alternative_endif
#else
@@ -367,6 +400,7 @@ alternative_endif
// disable interrupts before pulling preserved data off the stack
disable_irq x21
+ disable_nmi
kernel_exit 1
el1_sp_pc:
/*
@@ -407,10 +441,14 @@ ENDPROC(el1_sync)
el1_irq:
kernel_entry 1
enable_dbg
-#ifdef CONFIG_TRACE_IRQFLAGS
- bl trace_hardirqs_off
-#endif
+ trace_hardirqs_off x23
+ /*
+ * On systems with CONFIG_USE_ICC_SYSREGS_FOR_IRQFLAGS then
+ * we do not yet know if this IRQ is a pseudo-NMI or a normal
+ * interrupt. For that reason we must rely on the irq_handler to
+ * enable the NMI once the interrupt type is determined.
+ */
irq_handler
#ifdef CONFIG_PREEMPT
@@ -422,9 +460,9 @@ el1_irq:
bl el1_preempt
1:
#endif
-#ifdef CONFIG_TRACE_IRQFLAGS
- bl trace_hardirqs_on
-#endif
+
+ disable_nmi
+ trace_hardirqs_on x23
kernel_exit 1
ENDPROC(el1_irq)
@@ -519,6 +557,7 @@ el0_da:
*/
mrs x26, far_el1
// enable interrupts before calling the main handler
+ enable_nmi
enable_dbg_and_irq x0
ct_user_exit
bic x0, x26, #(0xff << 56)
@@ -532,6 +571,7 @@ el0_ia:
*/
mrs x26, far_el1
// enable interrupts before calling the main handler
+ enable_nmi
enable_dbg_and_irq x0
ct_user_exit
mov x0, x26
@@ -565,6 +605,7 @@ el0_sp_pc:
*/
mrs x26, far_el1
// enable interrupts before calling the main handler
+ enable_nmi
enable_dbg_and_irq x0
ct_user_exit
mov x0, x26
@@ -577,6 +618,7 @@ el0_undef:
* Undefined instruction
*/
// enable interrupts before calling the main handler
+ enable_nmi
enable_dbg_and_irq x0
ct_user_exit
mov x0, sp
@@ -609,16 +651,18 @@ el0_irq:
kernel_entry 0
el0_irq_naked:
enable_dbg
-#ifdef CONFIG_TRACE_IRQFLAGS
- bl trace_hardirqs_off
-#endif
-
+ trace_hardirqs_off x23
ct_user_exit
+
+ /*
+ * On systems with CONFIG_USE_ICC_SYSREGS_FOR_IRQFLAGS then
+ * we do not yet know if this IRQ is a pseudo-NMI or a normal
+ * interrupt. For that reason we must rely on the irq_handler to
+ * enable the NMI once the interrupt type is determined.
+ */
irq_handler
-#ifdef CONFIG_TRACE_IRQFLAGS
- bl trace_hardirqs_on
-#endif
+ trace_hardirqs_on x23
b ret_to_user
ENDPROC(el0_irq)
@@ -666,6 +710,7 @@ ret_fast_syscall:
and x2, x1, #_TIF_WORK_MASK
cbnz x2, work_pending
enable_step_tsk x1, x2
+ disable_nmi
kernel_exit 0
ret_fast_syscall_trace:
enable_irq x0 // enable interrupts
@@ -681,6 +726,7 @@ work_pending:
mov x0, sp // 'regs'
tst x2, #PSR_MODE_MASK // user mode regs?
b.ne no_work_pending // returning to kernel
+ enable_nmi
enable_irq x21 // enable interrupts for do_notify_resume()
bl do_notify_resume
b ret_to_user
@@ -697,6 +743,7 @@ ret_to_user:
cbnz x2, work_pending
enable_step_tsk x1, x2
no_work_pending:
+ disable_nmi
kernel_exit 0
ENDPROC(ret_to_user)
@@ -722,6 +769,7 @@ el0_svc:
mov sc_nr, #__NR_syscalls
el0_svc_naked: // compat entry point
stp x0, scno, [sp, #S_ORIG_X0] // save the original x0 and syscall number
+ enable_nmi
enable_dbg_and_irq x16
ct_user_exit 1
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 0f37a33499e2..d5539291ac55 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -804,13 +804,31 @@ int setup_profiling_timer(unsigned int multiplier)
return -EINVAL;
}
+/*
+ * IPI_CPU_BACKTRACE is either implemented either as a normal IRQ or,
+ * if the hardware can supports it, using a pseudo-NMI.
+ *
+ * The mechanism used to implement pseudo-NMI means that in both cases
+ * testing if the backtrace IPI is disabled requires us to check the
+ * PSR I bit. However in the later case we cannot use irqs_disabled()
+ * to check the I bit because, when the pseudo-NMI is active that
+ * function examines the GIC PMR instead.
+ */
+static unsigned long nmi_disabled(void)
+{
+ unsigned long flags;
+
+ asm volatile("mrs %0, daif" : "=r"(flags) :: "memory");
+ return flags & PSR_I_BIT;
+}
+
static void raise_nmi(cpumask_t *mask)
{
/*
* Generate the backtrace directly if we are running in a
* calling context that is not preemptible by the backtrace IPI.
*/
- if (cpumask_test_cpu(smp_processor_id(), mask) && irqs_disabled())
+ if (cpumask_test_cpu(smp_processor_id(), mask) && nmi_disabled())
nmi_cpu_backtrace(NULL);
smp_cross_call(mask, IPI_CPU_BACKTRACE);
diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index 48cc3dfe1a0a..a389a387c5a6 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -19,6 +19,7 @@
#include <linux/cpu_pm.h>
#include <linux/delay.h>
#include <linux/interrupt.h>
+#include <linux/nmi.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_irq.h>
@@ -409,10 +410,60 @@ static u64 gic_mpidr_to_affinity(u64 mpidr)
return aff;
}
+#ifdef CONFIG_USE_ICC_SYSREGS_FOR_IRQFLAGS
+static bool gic_handle_nmi(struct pt_regs *regs)
+{
+ u64 irqnr;
+ struct pt_regs *old_regs;
+
+ asm volatile("mrs_s %0, " __stringify(ICC_IAR1_EL1) : "=r"(irqnr));
+
+ /*
+ * If no IRQ is acknowledged at this point then we have entered the
+ * handler due to an normal interrupt (rather than a pseudo-NMI).
+ * If so then unmask the I-bit and return to normal handling.
+ */
+ if (irqnr == ICC_IAR1_EL1_SPURIOUS) {
+ asm volatile("msr daifclr, #2" : : : "memory");
+ return false;
+ }
+
+ old_regs = set_irq_regs(regs);
+ nmi_enter();
+
+ do {
+ if (SMP_IPI_NMI_MASK & (1 << irqnr)) {
+ gic_write_eoir(irqnr);
+ if (static_key_true(&supports_deactivate))
+ gic_write_dir(irqnr);
+ nmi_cpu_backtrace(regs);
+ } else if (unlikely(irqnr != ICC_IAR1_EL1_SPURIOUS)) {
+ gic_write_eoir(irqnr);
+ if (static_key_true(&supports_deactivate))
+ gic_write_dir(irqnr);
+ WARN_ONCE(true, "Unexpected NMI received!\n");
+ }
+
+ asm volatile("mrs_s %0, " __stringify(ICC_IAR1_EL1)
+ : "=r"(irqnr));
+ } while (irqnr != ICC_IAR1_EL1_SPURIOUS);
+
+ nmi_exit();
+ set_irq_regs(old_regs);
+
+ return true;
+}
+#else
+static bool gic_handle_nmi(struct pt_regs *regs) { return false; }
+#endif
+
static asmlinkage void __exception_irq_entry gic_handle_irq(struct pt_regs *regs)
{
u64 irqnr;
+ if (gic_handle_nmi(regs))
+ return;
+
do {
irqnr = gic_read_iar();
@@ -567,6 +618,7 @@ static int gic_dist_supports_lpis(void)
static void gic_cpu_init(void)
{
void __iomem *rbase;
+ unsigned long nmimask, hwirq;
/* Register ourselves with the rest of the world */
if (gic_populate_rdist())
@@ -584,6 +636,23 @@ static void gic_cpu_init(void)
/* initialise system registers */
gic_cpu_sys_reg_init();
+
+ /* Boost the priority of any IPI in the mask */
+ nmimask = SMP_IPI_NMI_MASK;
+ for_each_set_bit(hwirq, &nmimask, 16) {
+ unsigned int pri_reg = (hwirq / 4) * 4;
+ u32 pri_mask = BIT(6 + ((hwirq % 4) * 8));
+ u32 pri_val = readl_relaxed(rbase + GIC_DIST_PRI + pri_reg);
+ u32 actual;
+
+ pri_mask |= BIT(7 + ((hwirq % 4) * 8));
+ pri_val &= ~pri_mask; /* priority boost */
+ writel_relaxed(pri_val, rbase + GIC_DIST_PRI + pri_reg);
+
+ actual = readl_relaxed(rbase + GIC_DIST_PRI + pri_reg);
+ }
+ gic_dist_wait_for_rwp();
+ gic_redist_wait_for_rwp();
}
#ifdef CONFIG_SMP
--
2.4.3
--
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