[PATCH 2/3] arm64: Consolidate hotplug notifier for instruction emulation

Suzuki K. Poulose
2015-01-15T12:36:19Z

From: "Suzuki K. Poulose" <suzuki.poulose@arm.com>

As of now each insn_emulation has a cpu hotplug notifier that
enables/disables the CPU feature bit for the functionality. This
patch re-arranges the code, such that there is only one notifier
that runs through the list of registered emulation hooks and runs
their corresponding set_hw_mode.

We do nothing when a CPU is dying as we will set the appropriate bits
as it comes back online based on the state of the hooks.

Signed-off-by: Suzuki K. Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
---
Documentation/arm64/legacy_instructions.txt | 4 +
arch/arm64/include/asm/cpufeature.h | 2 +
arch/arm64/kernel/armv8_deprecated.c | 113 +++++++++++++++------------
3 files changed, 69 insertions(+), 50 deletions(-)

diff --git a/Documentation/arm64/legacy_instructions.txt b/Documentation/arm64/legacy_instructions.txt
index a3b3da2..0a4dc26 100644
--- a/Documentation/arm64/legacy_instructions.txt
+++ b/Documentation/arm64/legacy_instructions.txt
@@ -27,6 +27,10 @@ behaviours and the corresponding values of the sysctl nodes -
instructions. Using hardware execution generally provides better
performance, but at the loss of ability to gather runtime statistics
about the use of the deprecated instructions.
+ Note: Emulation of a deprecated instruction depends on the availability
+ of the feature on all the active CPUs. In case of CPU hotplug, if a new
+ CPU doesn't support a feature, it could result in the abortion of the
+ hotplug operation.

The default mode depends on the status of the instruction in the
architecture. Deprecated instructions should default to emulation
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index c7f68d1..a56b45f 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -29,6 +29,8 @@
#define ID_AA64MMFR0_EL1_BigEndEL0 (0x1UL << 16)
#define ID_AA64MMFR0_EL1_BigEnd (0x1UL << 8)

+#define SCTLR_EL1_CP15BEN (1 << 5)
+
#ifndef __ASSEMBLY__

extern DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);
diff --git a/arch/arm64/kernel/armv8_deprecated.c b/arch/arm64/kernel/armv8_deprecated.c
index c363671..be64218 100644
--- a/arch/arm64/kernel/armv8_deprecated.c
+++ b/arch/arm64/kernel/armv8_deprecated.c
@@ -19,6 +19,7 @@
#include <asm/system_misc.h>
#include <asm/traps.h>
#include <asm/uaccess.h>
+#include <asm/cpufeature.h>

#define CREATE_TRACE_POINTS
#include "trace-events-emulation.h"
@@ -46,7 +47,7 @@ struct insn_emulation_ops {
const char *name;
enum legacy_insn_status status;
struct undef_hook *hooks;
- int (*set_hw_mode)(bool enable);
+ int (*set_hw_mode)(void *enable);
};

struct insn_emulation {
@@ -85,6 +86,40 @@ static void remove_emulation_hooks(struct insn_emulation_ops *ops)
pr_notice("Removed %s emulation handler\n", ops->name);
}

+/* Run set_hw_mode(mode) on all active CPUs */
+static int run_all_cpu_set_hw_mode(struct insn_emulation *insn, bool enable)
+{
+ void (*set_hw_mode)(void *) = (void (*) (void *))insn->ops->set_hw_mode;
+ if (!set_hw_mode)
+ return -EINVAL;
+ on_each_cpu(set_hw_mode, (void *)enable, true);
+ return 0;
+}
+
+/*
+ * Run set_hw_mode for all insns on a starting CPU.
+ * Returns:
+ * 0 - If all the hooks ran successfully.
+ * -EINVAL - At least one hook is not supported by the CPU.
+ * abort the hotplug.
+ */
+static int run_all_insn_set_hw_mode(void)
+{
+ int rc = 0;
+ unsigned long flags;
+ struct insn_emulation *insn;
+
+ raw_spin_lock_irqsave(&insn_emulation_lock, flags);
+ list_for_each_entry(insn, &insn_emulation, node) {
+ bool hw_mode = (insn->current_mode == INSN_HW);
+ if (insn->ops->set_hw_mode &&
+ insn->ops->set_hw_mode((void*)hw_mode))
+ rc = -EINVAL;
+ }
+ raw_spin_unlock_irqrestore(&insn_emulation_lock, flags);
+ return rc;
+}
+
static int update_insn_emulation_mode(struct insn_emulation *insn,
enum insn_emulation_mode prev)
{
@@ -97,10 +132,8 @@ static int update_insn_emulation_mode(struct insn_emulation *insn,
remove_emulation_hooks(insn->ops);
break;
case INSN_HW:
- if (insn->ops->set_hw_mode) {
- insn->ops->set_hw_mode(false);
+ if (!run_all_cpu_set_hw_mode(insn, false))
pr_notice("Disabled %s support\n", insn->ops->name);
- }
break;
}

@@ -111,10 +144,9 @@ static int update_insn_emulation_mode(struct insn_emulation *insn,
register_emulation_hooks(insn->ops);
break;
case INSN_HW:
- if (insn->ops->set_hw_mode && insn->ops->set_hw_mode(true))
+ ret = run_all_cpu_set_hw_mode(insn, true);
+ if (!ret)
pr_notice("Enabled %s support\n", insn->ops->name);
- else
- ret = -EINVAL;
break;
}

@@ -133,6 +165,8 @@ static void register_insn_emulation(struct insn_emulation_ops *ops)
switch (ops->status) {
case INSN_DEPRECATED:
insn->current_mode = INSN_EMULATE;
+ /* Disable the HW mode if it was turned on at early boot time */
+ run_all_cpu_set_hw_mode(insn, false);
insn->max = INSN_HW;
break;
case INSN_OBSOLETE:
@@ -453,8 +487,6 @@ ret:
return 0;
}

-#define SCTLR_EL1_CP15BEN (1 << 5)
-
static inline void config_sctlr_el1(u32 clear, u32 set)
{
u32 val;
@@ -465,48 +497,13 @@ static inline void config_sctlr_el1(u32 clear, u32 set)
asm volatile("msr sctlr_el1, %0" : : "r" (val));
}

-static void enable_cp15_ben(void *info)
-{
- config_sctlr_el1(0, SCTLR_EL1_CP15BEN);
-}
-
-static void disable_cp15_ben(void *info)
+static int cp15_barrier_set_hw_mode(void *enable)
{
- config_sctlr_el1(SCTLR_EL1_CP15BEN, 0);
-}
-
-static int cpu_hotplug_notify(struct notifier_block *b,
- unsigned long action, void *hcpu)
-{
- switch (action) {
- case CPU_STARTING:
- case CPU_STARTING_FROZEN:
- enable_cp15_ben(NULL);
- return NOTIFY_DONE;
- case CPU_DYING:
- case CPU_DYING_FROZEN:
- disable_cp15_ben(NULL);
- return NOTIFY_DONE;
- }
-
- return NOTIFY_OK;
-}
-
-static struct notifier_block cpu_hotplug_notifier = {
- .notifier_call = cpu_hotplug_notify,
-};
-
-static int cp15_barrier_set_hw_mode(bool enable)
-{
- if (enable) {
- register_cpu_notifier(&cpu_hotplug_notifier);
- on_each_cpu(enable_cp15_ben, NULL, true);
- } else {
- unregister_cpu_notifier(&cpu_hotplug_notifier);
- on_each_cpu(disable_cp15_ben, NULL, true);
- }
-
- return true;
+ if (enable)
+ config_sctlr_el1(0, SCTLR_EL1_CP15BEN);
+ else
+ config_sctlr_el1(SCTLR_EL1_CP15BEN, 0);
+ return 0;
}

static struct undef_hook cp15_barrier_hooks[] = {
@@ -534,6 +531,21 @@ static struct insn_emulation_ops cp15_barrier_ops = {
.set_hw_mode = cp15_barrier_set_hw_mode,
};

+static int insn_cpu_hotplug_notify(struct notifier_block *b,
+ unsigned long action, void *hcpu)
+{
+ int rc = 0;
+ if ((action & ~CPU_TASKS_FROZEN) == CPU_STARTING)
+ rc = run_all_insn_set_hw_mode();
+
+ /* Abort the CPU hotplug if there is an incompatibility */
+ return notifier_from_errno(rc);
+}
+
+static struct notifier_block insn_cpu_hotplug_notifier = {
+ .notifier_call = insn_cpu_hotplug_notify,
+};
+
/*
* Invoked as late_initcall, since not needed before init spawned.
*/
@@ -545,6 +557,7 @@ static int __init armv8_deprecated_init(void)
if (IS_ENABLED(CONFIG_CP15_BARRIER_EMULATION))
register_insn_emulation(&cp15_barrier_ops);

+ register_cpu_notifier(&insn_cpu_hotplug_notifier);
register_insn_emulation_sysctl(ctl_abi);

return 0;
--
1.7.9.5