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Groups > linux.kernel > #1387565 > unrolled thread

[PATCH v5 0/5] arm64: Fix behavior of maxcpus=n

Started bySuzuki K Poulose <suzuki.poulose@arm.com>
First post2016-04-26 16:50 +0200
Last post2016-04-26 17:00 +0200
Articles 5 — 3 participants

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Contents

  [PATCH v5 0/5] arm64: Fix behavior of maxcpus=n Suzuki K Poulose <suzuki.poulose@arm.com> - 2016-04-26 16:50 +0200
    [PATCH v5 1/5] arm64: cpufeature: Add scope for capability check Suzuki K Poulose <suzuki.poulose@arm.com> - 2016-04-26 16:50 +0200
    Re: [PATCH v5 0/5] arm64: Fix behavior of maxcpus=n Will Deacon <will.deacon@arm.com> - 2016-04-26 17:00 +0200
      Re: [PATCH v5 0/5] arm64: Fix behavior of maxcpus=n Suzuki K Poulose <Suzuki.Poulose@arm.com> - 2016-04-26 17:00 +0200
    [PATCH v5 2/5] arm64: Allow a capability to be checked on a single CPU Suzuki K Poulose <suzuki.poulose@arm.com> - 2016-04-26 17:00 +0200

#1387565 — [PATCH v5 0/5] arm64: Fix behavior of maxcpus=n

FromSuzuki K Poulose <suzuki.poulose@arm.com>
Date2016-04-26 16:50 +0200
Subject[PATCH v5 0/5] arm64: Fix behavior of maxcpus=n
Message-ID<rsctj-Xx-7@gated-at.bofh.it>
This series is an attempt at fixing the maxcpus=n behavior
on arm64. So far we have disabled hotplugging a CPU > n,
when maxcpus=n is in effect, due to following reasons.

 1) Possible cpu feature incompatibilities with the new CPU
    in heterogeneous systems.
 2) New CPU requiring an errata work around which was not detected
    (and the code patched in) at boot time.
 3) Failure to initialise the PMU in case the supported CPUs are
    not online while probing the PMU.

(1) has been mostly solved with our early CPU feature verification
support. This series tries to address (2) & (3).

(2) is solved by iterating over the known erratas and checking if
the new CPU requires an errata not set in the cpu_hwcaps, failing
which, we kill the CPU. We plan to fix this properly by retaining
the CPU errata work arounds and apply the required at runtime.

(3) is ignored and will not be fixed as there is no reliable way of
knowing if there would be a CPU that will be online to support the
PMU.

In the process, also restores the capability to check GIC interface settings
by the firmware on individual CPUs.

Tested on Juno with maxcpus=2 (enables A57 cores and A57-PMU) and
maxcpus=1 (disables both A57 cores and A57-PMU).

This series applies on aarch64/for-next/core :

The tree is available here :
	git://linux-arm.org/linux-skp.git maxcpus/v5

Changes since V4:
 - Address Catalin's comments
 - Rebased to aarch64 for-next/core
 - Add Reviewed/Acked bys.


Marc Zyngier (2):
  arm64: Allow a capability to be checked on a single CPU
  irqchip/gic: Restore CPU interface checking

Suzuki K Poulose (3):
  arm64: cpufeature: Add scope for capability check
  arm64: Verify CPU errata work arounds on hotplugged CPU
  arm64: Fix behavior of maxcpus=N

 arch/arm64/include/asm/cpufeature.h |   12 ++-
 arch/arm64/kernel/cpu_errata.c      |   24 +++++-
 arch/arm64/kernel/cpufeature.c      |  150 +++++++++++++++++++++--------------
 arch/arm64/kernel/smp.c             |   18 +----
 drivers/irqchip/irq-gic.c           |    5 +-
 5 files changed, 128 insertions(+), 81 deletions(-)

-- 
1.7.9.5

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#1387570 — [PATCH v5 1/5] arm64: cpufeature: Add scope for capability check

FromSuzuki K Poulose <suzuki.poulose@arm.com>
Date2016-04-26 16:50 +0200
Subject[PATCH v5 1/5] arm64: cpufeature: Add scope for capability check
Message-ID<rsctl-Xx-45@gated-at.bofh.it>
In reply to#1387565
Add scope parameter to the arm64_cpu_capabilities::matches(), so that
this can be reused for checking the capability on a given CPU vs the
system wide. The system uses the default scope associated with the
capability for initialising the CPU_HWCAPs and ELF_HWCAPs.

Cc: James Morse <james.morse@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Andre Przywara <andre.przywara@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
 arch/arm64/include/asm/cpufeature.h |    9 ++-
 arch/arm64/kernel/cpu_errata.c      |    4 +-
 arch/arm64/kernel/cpufeature.c      |  131 +++++++++++++++++++----------------
 3 files changed, 83 insertions(+), 61 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index ca8fb4b..e501e4a 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -78,10 +78,17 @@ struct arm64_ftr_reg {
 	struct arm64_ftr_bits	*ftr_bits;
 };
 
+/* scope of capability check */
+enum {
+	SCOPE_SYSTEM,
+	SCOPE_LOCAL_CPU,
+};
+
 struct arm64_cpu_capabilities {
 	const char *desc;
 	u16 capability;
-	bool (*matches)(const struct arm64_cpu_capabilities *);
+	int def_scope;			/* default scope */
+	bool (*matches)(const struct arm64_cpu_capabilities *caps, int scope);
 	void (*enable)(void *);		/* Called on all active CPUs */
 	union {
 		struct {	/* To be used for erratum handling only */
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 06afd04..2fdecd7 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -22,14 +22,16 @@
 #include <asm/cpufeature.h>
 
 static bool __maybe_unused
-is_affected_midr_range(const struct arm64_cpu_capabilities *entry)
+is_affected_midr_range(const struct arm64_cpu_capabilities *entry, int scope)
 {
+	WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());
 	return MIDR_IS_CPU_MODEL_RANGE(read_cpuid_id(), entry->midr_model,
 				       entry->midr_range_min,
 				       entry->midr_range_max);
 }
 
 #define MIDR_RANGE(model, min, max) \
+	.def_scope = SCOPE_LOCAL_CPU, \
 	.matches = is_affected_midr_range, \
 	.midr_model = model, \
 	.midr_range_min = min, \
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 8e62d61..54abd9b 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -71,7 +71,8 @@ DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);
 
 /* meta feature for alternatives */
 static bool __maybe_unused
-cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry);
+cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused);
+
 
 static struct arm64_ftr_bits ftr_id_aa64isar0[] = {
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 32, 32, 0),
@@ -626,6 +627,49 @@ u64 read_system_reg(u32 id)
 	return regp->sys_val;
 }
 
+/*
+ * __raw_read_system_reg() - Used by a STARTING cpu before cpuinfo is populated.
+ * Read the system register on the current CPU
+ */
+static u64 __raw_read_system_reg(u32 sys_id)
+{
+	switch (sys_id) {
+	case SYS_ID_PFR0_EL1:		return read_cpuid(ID_PFR0_EL1);
+	case SYS_ID_PFR1_EL1:		return read_cpuid(ID_PFR1_EL1);
+	case SYS_ID_DFR0_EL1:		return read_cpuid(ID_DFR0_EL1);
+	case SYS_ID_MMFR0_EL1:		return read_cpuid(ID_MMFR0_EL1);
+	case SYS_ID_MMFR1_EL1:		return read_cpuid(ID_MMFR1_EL1);
+	case SYS_ID_MMFR2_EL1:		return read_cpuid(ID_MMFR2_EL1);
+	case SYS_ID_MMFR3_EL1:		return read_cpuid(ID_MMFR3_EL1);
+	case SYS_ID_ISAR0_EL1:		return read_cpuid(ID_ISAR0_EL1);
+	case SYS_ID_ISAR1_EL1:		return read_cpuid(ID_ISAR1_EL1);
+	case SYS_ID_ISAR2_EL1:		return read_cpuid(ID_ISAR2_EL1);
+	case SYS_ID_ISAR3_EL1:		return read_cpuid(ID_ISAR3_EL1);
+	case SYS_ID_ISAR4_EL1:		return read_cpuid(ID_ISAR4_EL1);
+	case SYS_ID_ISAR5_EL1:		return read_cpuid(ID_ISAR4_EL1);
+	case SYS_MVFR0_EL1:		return read_cpuid(MVFR0_EL1);
+	case SYS_MVFR1_EL1:		return read_cpuid(MVFR1_EL1);
+	case SYS_MVFR2_EL1:		return read_cpuid(MVFR2_EL1);
+
+	case SYS_ID_AA64PFR0_EL1:	return read_cpuid(ID_AA64PFR0_EL1);
+	case SYS_ID_AA64PFR1_EL1:	return read_cpuid(ID_AA64PFR0_EL1);
+	case SYS_ID_AA64DFR0_EL1:	return read_cpuid(ID_AA64DFR0_EL1);
+	case SYS_ID_AA64DFR1_EL1:	return read_cpuid(ID_AA64DFR0_EL1);
+	case SYS_ID_AA64MMFR0_EL1:	return read_cpuid(ID_AA64MMFR0_EL1);
+	case SYS_ID_AA64MMFR1_EL1:	return read_cpuid(ID_AA64MMFR1_EL1);
+	case SYS_ID_AA64MMFR2_EL1:	return read_cpuid(ID_AA64MMFR2_EL1);
+	case SYS_ID_AA64ISAR0_EL1:	return read_cpuid(ID_AA64ISAR0_EL1);
+	case SYS_ID_AA64ISAR1_EL1:	return read_cpuid(ID_AA64ISAR1_EL1);
+
+	case SYS_CNTFRQ_EL0:		return read_cpuid(CNTFRQ_EL0);
+	case SYS_CTR_EL0:		return read_cpuid(CTR_EL0);
+	case SYS_DCZID_EL0:		return read_cpuid(DCZID_EL0);
+	default:
+		BUG();
+		return 0;
+	}
+}
+
 #include <linux/irqchip/arm-gic-v3.h>
 
 static bool
@@ -637,19 +681,24 @@ feature_matches(u64 reg, const struct arm64_cpu_capabilities *entry)
 }
 
 static bool
-has_cpuid_feature(const struct arm64_cpu_capabilities *entry)
+has_cpuid_feature(const struct arm64_cpu_capabilities *entry, int scope)
 {
 	u64 val;
 
-	val = read_system_reg(entry->sys_reg);
+	WARN_ON(scope == SCOPE_LOCAL_CPU && preemptible());
+	if (scope == SCOPE_SYSTEM)
+		val = read_system_reg(entry->sys_reg);
+	else
+		val = __raw_read_system_reg(entry->sys_reg);
+
 	return feature_matches(val, entry);
 }
 
-static bool has_useable_gicv3_cpuif(const struct arm64_cpu_capabilities *entry)
+static bool has_useable_gicv3_cpuif(const struct arm64_cpu_capabilities *entry, int scope)
 {
 	bool has_sre;
 
-	if (!has_cpuid_feature(entry))
+	if (!has_cpuid_feature(entry, scope))
 		return false;
 
 	has_sre = gic_enable_sre();
@@ -660,7 +709,7 @@ static bool has_useable_gicv3_cpuif(const struct arm64_cpu_capabilities *entry)
 	return has_sre;
 }
 
-static bool has_no_hw_prefetch(const struct arm64_cpu_capabilities *entry)
+static bool has_no_hw_prefetch(const struct arm64_cpu_capabilities *entry, int __unused)
 {
 	u32 midr = read_cpuid_id();
 	u32 rv_min, rv_max;
@@ -672,7 +721,7 @@ static bool has_no_hw_prefetch(const struct arm64_cpu_capabilities *entry)
 	return MIDR_IS_CPU_MODEL_RANGE(midr, MIDR_THUNDERX, rv_min, rv_max);
 }
 
-static bool runs_at_el2(const struct arm64_cpu_capabilities *entry)
+static bool runs_at_el2(const struct arm64_cpu_capabilities *entry, int __unused)
 {
 	return is_kernel_in_hyp_mode();
 }
@@ -681,6 +730,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 	{
 		.desc = "GIC system register CPU interface",
 		.capability = ARM64_HAS_SYSREG_GIC_CPUIF,
+		.def_scope = SCOPE_SYSTEM,
 		.matches = has_useable_gicv3_cpuif,
 		.sys_reg = SYS_ID_AA64PFR0_EL1,
 		.field_pos = ID_AA64PFR0_GIC_SHIFT,
@@ -691,6 +741,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 	{
 		.desc = "Privileged Access Never",
 		.capability = ARM64_HAS_PAN,
+		.def_scope = SCOPE_SYSTEM,
 		.matches = has_cpuid_feature,
 		.sys_reg = SYS_ID_AA64MMFR1_EL1,
 		.field_pos = ID_AA64MMFR1_PAN_SHIFT,
@@ -703,6 +754,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 	{
 		.desc = "LSE atomic instructions",
 		.capability = ARM64_HAS_LSE_ATOMICS,
+		.def_scope = SCOPE_SYSTEM,
 		.matches = has_cpuid_feature,
 		.sys_reg = SYS_ID_AA64ISAR0_EL1,
 		.field_pos = ID_AA64ISAR0_ATOMICS_SHIFT,
@@ -713,12 +765,14 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 	{
 		.desc = "Software prefetching using PRFM",
 		.capability = ARM64_HAS_NO_HW_PREFETCH,
+		.def_scope = SCOPE_SYSTEM,
 		.matches = has_no_hw_prefetch,
 	},
 #ifdef CONFIG_ARM64_UAO
 	{
 		.desc = "User Access Override",
 		.capability = ARM64_HAS_UAO,
+		.def_scope = SCOPE_SYSTEM,
 		.matches = has_cpuid_feature,
 		.sys_reg = SYS_ID_AA64MMFR2_EL1,
 		.field_pos = ID_AA64MMFR2_UAO_SHIFT,
@@ -729,17 +783,20 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 #ifdef CONFIG_ARM64_PAN
 	{
 		.capability = ARM64_ALT_PAN_NOT_UAO,
+		.def_scope = SCOPE_SYSTEM,
 		.matches = cpufeature_pan_not_uao,
 	},
 #endif /* CONFIG_ARM64_PAN */
 	{
 		.desc = "Virtualization Host Extensions",
 		.capability = ARM64_HAS_VIRT_HOST_EXTN,
+		.def_scope = SCOPE_SYSTEM,
 		.matches = runs_at_el2,
 	},
 	{
 		.desc = "32-bit EL0 Support",
 		.capability = ARM64_HAS_32BIT_EL0,
+		.def_scope = SCOPE_SYSTEM,
 		.matches = has_cpuid_feature,
 		.sys_reg = SYS_ID_AA64PFR0_EL1,
 		.sign = FTR_UNSIGNED,
@@ -752,6 +809,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 #define HWCAP_CAP(reg, field, s, min_value, type, cap)	\
 	{							\
 		.desc = #cap,					\
+		.def_scope = SCOPE_SYSTEM,			\
 		.matches = has_cpuid_feature,			\
 		.sys_reg = reg,					\
 		.field_pos = field,				\
@@ -834,7 +892,7 @@ static bool cpus_have_elf_hwcap(const struct arm64_cpu_capabilities *cap)
 static void __init setup_elf_hwcaps(const struct arm64_cpu_capabilities *hwcaps)
 {
 	for (; hwcaps->matches; hwcaps++)
-		if (hwcaps->matches(hwcaps))
+		if (hwcaps->matches(hwcaps, hwcaps->def_scope))
 			cap_set_elf_hwcap(hwcaps);
 }
 
@@ -842,7 +900,7 @@ void update_cpu_capabilities(const struct arm64_cpu_capabilities *caps,
 			    const char *info)
 {
 	for (; caps->matches; caps++) {
-		if (!caps->matches(caps))
+		if (!caps->matches(caps, caps->def_scope))
 			continue;
 
 		if (!cpus_have_cap(caps->capability) && caps->desc)
@@ -879,48 +937,6 @@ static inline void set_sys_caps_initialised(void)
 }
 
 /*
- * __raw_read_system_reg() - Used by a STARTING cpu before cpuinfo is populated.
- */
-static u64 __raw_read_system_reg(u32 sys_id)
-{
-	switch (sys_id) {
-	case SYS_ID_PFR0_EL1:		return read_cpuid(ID_PFR0_EL1);
-	case SYS_ID_PFR1_EL1:		return read_cpuid(ID_PFR1_EL1);
-	case SYS_ID_DFR0_EL1:		return read_cpuid(ID_DFR0_EL1);
-	case SYS_ID_MMFR0_EL1:		return read_cpuid(ID_MMFR0_EL1);
-	case SYS_ID_MMFR1_EL1:		return read_cpuid(ID_MMFR1_EL1);
-	case SYS_ID_MMFR2_EL1:		return read_cpuid(ID_MMFR2_EL1);
-	case SYS_ID_MMFR3_EL1:		return read_cpuid(ID_MMFR3_EL1);
-	case SYS_ID_ISAR0_EL1:		return read_cpuid(ID_ISAR0_EL1);
-	case SYS_ID_ISAR1_EL1:		return read_cpuid(ID_ISAR1_EL1);
-	case SYS_ID_ISAR2_EL1:		return read_cpuid(ID_ISAR2_EL1);
-	case SYS_ID_ISAR3_EL1:		return read_cpuid(ID_ISAR3_EL1);
-	case SYS_ID_ISAR4_EL1:		return read_cpuid(ID_ISAR4_EL1);
-	case SYS_ID_ISAR5_EL1:		return read_cpuid(ID_ISAR4_EL1);
-	case SYS_MVFR0_EL1:		return read_cpuid(MVFR0_EL1);
-	case SYS_MVFR1_EL1:		return read_cpuid(MVFR1_EL1);
-	case SYS_MVFR2_EL1:		return read_cpuid(MVFR2_EL1);
-
-	case SYS_ID_AA64PFR0_EL1:	return read_cpuid(ID_AA64PFR0_EL1);
-	case SYS_ID_AA64PFR1_EL1:	return read_cpuid(ID_AA64PFR0_EL1);
-	case SYS_ID_AA64DFR0_EL1:	return read_cpuid(ID_AA64DFR0_EL1);
-	case SYS_ID_AA64DFR1_EL1:	return read_cpuid(ID_AA64DFR0_EL1);
-	case SYS_ID_AA64MMFR0_EL1:	return read_cpuid(ID_AA64MMFR0_EL1);
-	case SYS_ID_AA64MMFR1_EL1:	return read_cpuid(ID_AA64MMFR1_EL1);
-	case SYS_ID_AA64MMFR2_EL1:	return read_cpuid(ID_AA64MMFR2_EL1);
-	case SYS_ID_AA64ISAR0_EL1:	return read_cpuid(ID_AA64ISAR0_EL1);
-	case SYS_ID_AA64ISAR1_EL1:	return read_cpuid(ID_AA64ISAR1_EL1);
-
-	case SYS_CNTFRQ_EL0:		return read_cpuid(CNTFRQ_EL0);
-	case SYS_CTR_EL0:		return read_cpuid(CTR_EL0);
-	case SYS_DCZID_EL0:		return read_cpuid(DCZID_EL0);
-	default:
-		BUG();
-		return 0;
-	}
-}
-
-/*
  * Check for CPU features that are used in early boot
  * based on the Boot CPU value.
  */
@@ -934,28 +950,25 @@ static void
 verify_local_elf_hwcaps(const struct arm64_cpu_capabilities *caps)
 {
 
-	for (; caps->matches; caps++) {
-		if (!cpus_have_elf_hwcap(caps))
-			continue;
-		if (!feature_matches(__raw_read_system_reg(caps->sys_reg), caps)) {
+	for (; caps->matches; caps++)
+		if (cpus_have_elf_hwcap(caps) && !caps->matches(caps, SCOPE_LOCAL_CPU)) {
 			pr_crit("CPU%d: missing HWCAP: %s\n",
 					smp_processor_id(), caps->desc);
 			cpu_die_early();
 		}
-	}
 }
 
 static void
 verify_local_cpu_features(const struct arm64_cpu_capabilities *caps)
 {
 	for (; caps->matches; caps++) {
-		if (!cpus_have_cap(caps->capability) || !caps->sys_reg)
+		if (!cpus_have_cap(caps->capability))
 			continue;
 		/*
 		 * If the new CPU misses an advertised feature, we cannot proceed
 		 * further, park the cpu.
 		 */
-		if (!feature_matches(__raw_read_system_reg(caps->sys_reg), caps)) {
+		if (!caps->matches(caps, SCOPE_LOCAL_CPU)) {
 			pr_crit("CPU%d: missing feature: %s\n",
 					smp_processor_id(), caps->desc);
 			cpu_die_early();
@@ -1026,7 +1039,7 @@ void __init setup_cpu_features(void)
 }
 
 static bool __maybe_unused
-cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry)
+cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused)
 {
 	return (cpus_have_cap(ARM64_HAS_PAN) && !cpus_have_cap(ARM64_HAS_UAO));
 }
-- 
1.7.9.5

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#1387572

FromWill Deacon <will.deacon@arm.com>
Date2016-04-26 17:00 +0200
Message-ID<rscCZ-11Z-7@gated-at.bofh.it>
In reply to#1387565
On Tue, Apr 26, 2016 at 03:48:55PM +0100, Suzuki K Poulose wrote:
> This series is an attempt at fixing the maxcpus=n behavior
> on arm64. So far we have disabled hotplugging a CPU > n,
> when maxcpus=n is in effect, due to following reasons.
> 
>  1) Possible cpu feature incompatibilities with the new CPU
>     in heterogeneous systems.
>  2) New CPU requiring an errata work around which was not detected
>     (and the code patched in) at boot time.
>  3) Failure to initialise the PMU in case the supported CPUs are
>     not online while probing the PMU.
> 
> (1) has been mostly solved with our early CPU feature verification
> support. This series tries to address (2) & (3).
> 
> (2) is solved by iterating over the known erratas and checking if
> the new CPU requires an errata not set in the cpu_hwcaps, failing
> which, we kill the CPU. We plan to fix this properly by retaining
> the CPU errata work arounds and apply the required at runtime.
> 
> (3) is ignored and will not be fixed as there is no reliable way of
> knowing if there would be a CPU that will be online to support the
> PMU.
> 
> In the process, also restores the capability to check GIC interface settings
> by the firmware on individual CPUs.
> 
> Tested on Juno with maxcpus=2 (enables A57 cores and A57-PMU) and
> maxcpus=1 (disables both A57 cores and A57-PMU).
> 
> This series applies on aarch64/for-next/core :
> 
> The tree is available here :
> 	git://linux-arm.org/linux-skp.git maxcpus/v5
> 
> Changes since V4:
>  - Address Catalin's comments
>  - Rebased to aarch64 for-next/core
>  - Add Reviewed/Acked bys.

I merged this yesterday onto for-next/core. Please can you check that
I fixed everything up that you expected?

Will

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#1387583

FromSuzuki K Poulose <Suzuki.Poulose@arm.com>
Date2016-04-26 17:00 +0200
Message-ID<rscD0-11Z-39@gated-at.bofh.it>
In reply to#1387572
On 26/04/16 15:50, Will Deacon wrote:

>> Changes since V4:
>>   - Address Catalin's comments
>>   - Rebased to aarch64 for-next/core
>>   - Add Reviewed/Acked bys.
>
> I merged this yesterday onto for-next/core. Please can you check that
> I fixed everything up that you expected?

Just did a git diff and it looks alright. I pulled it yesterday before the push and hence missed
it, may be should have done dsb() today before sending ;-)

Thanks
Suzuki

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#1387585 — [PATCH v5 2/5] arm64: Allow a capability to be checked on a single CPU

FromSuzuki K Poulose <suzuki.poulose@arm.com>
Date2016-04-26 17:00 +0200
Subject[PATCH v5 2/5] arm64: Allow a capability to be checked on a single CPU
Message-ID<rscD1-11Z-45@gated-at.bofh.it>
In reply to#1387565
From: Marc Zyngier <marc.zyngier@arm.com>

Now that the capabilities are only available once all the CPUs
have booted, we're unable to check for a particular feature
in any subsystem that gets initialized before then.

In order to support this, introduce a local_cpu_has_cap() function
that tests for the presence of a given capability independently
of the whole framework.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
[ Added preemptible() check ]
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
 arch/arm64/include/asm/cpufeature.h |    2 ++
 arch/arm64/kernel/cpufeature.c      |   18 ++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index e501e4a..d39db63 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -109,6 +109,8 @@ struct arm64_cpu_capabilities {
 
 extern DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);
 
+bool this_cpu_has_cap(unsigned int cap);
+
 static inline bool cpu_have_feature(unsigned int num)
 {
 	return elf_hwcap & (1UL << num);
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 54abd9b..2b09dc4 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1010,6 +1010,24 @@ static void __init setup_feature_capabilities(void)
 	enable_cpu_capabilities(arm64_features);
 }
 
+/*
+ * Check if the current CPU has a given feature capability.
+ * Should be called from non-preemptible context.
+ */
+bool this_cpu_has_cap(unsigned int cap)
+{
+	const struct arm64_cpu_capabilities *caps;
+
+	if (WARN_ON(preemptible()))
+		return false;
+
+	for (caps = arm64_features; caps->desc; caps++)
+		if (caps->capability == cap && caps->matches)
+			return caps->matches(caps, SCOPE_LOCAL_CPU);
+
+	return false;
+}
+
 void __init setup_cpu_features(void)
 {
 	u32 cwg;
-- 
1.7.9.5

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