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SubjectRe: [PATCH v2 05/20] arm64: capabilities: Add flags to handle the conflicts on late CPU
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On 07/02/18 10:38, Dave Martin wrote:
> On Wed, Jan 31, 2018 at 06:27:52PM +0000, Suzuki K Poulose wrote:
>> When a CPU is brought up, it is checked against the caps that are
>> known to be enabled on the system (via verify_local_cpu_capabilities()).
>> Based on the state of the capability on the CPU vs. that of System we
>> could have the following combinations of conflict.
>>
>> x-----------------------------x
>> | Type | System | Late CPU |
>> |-----------------------------|
>> | a | y | n |
>> |-----------------------------|
>> | b | n | y |
>> x-----------------------------x
>>
>> Case (a) is not permitted for caps which are system features, which the
>> system expects all the CPUs to have (e.g VHE). While (a) is ignored for
>> all errata work arounds. However, there could be exceptions to the plain
>> filtering approach. e.g, KPTI is an optional feature for a late CPU as
>> long as the system already enables it.
>>
>> Case (b) is not permitted for errata work arounds which requires some work
>> around, which cannot be delayed. And we ignore (b) for features. Here, yet
>
> Nit, maybe:
>
> "Case (b) is not permitted for any errata workaround that cannot be
> activated if the kernel has finished booting and has not already enabled
> it."

Nit^2: I think it would suffice to say "...that cannot be activated
after the kernel has finished booting." - since we don't really have the
concept of *de*activating workarounds, it is already implicit in that
statement that the one in question wasn't activated *before* the kernel
finished booting.

Robin.

>> again, KPTI is an exception, where if a late CPU needs KPTI we are too late
>> to enable it (because we change the allocation of ASIDs etc).
>>
>> Add two different flags to indicate how the conflict should be handled.
>>
>> ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU - CPUs may have the capability
>> ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU - CPUs may not have the cappability.
>>
>> Now that we have the flags to describe the behavior of the errata and
>> the features, as we treat them, define types for ERRATUM and FEATURE.
>>
>> Cc: Dave Martin <dave.martin@arm.com>
>> Cc: Will Deacon <will.deacon@arm.com>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>
> All my suggestions in this patch are rewordings of comments, so they're
> not vital, and anyway you may disagree that they make the meaning
> clearer. So I don't think they're essential.
>
> For the actual code
>
> Reviewed-by: Dave Martin <Dave.Martin@arm.com>
>
>> ---
>> arch/arm64/include/asm/cpufeature.h | 61 ++++++++++++++++++++++++++++++++++++-
>> arch/arm64/kernel/cpu_errata.c | 8 ++---
>> arch/arm64/kernel/cpufeature.c | 30 +++++++++---------
>> 3 files changed, 79 insertions(+), 20 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
>> index 05da54f1b4c7..7460b1f7e611 100644
>> --- a/arch/arm64/include/asm/cpufeature.h
>> +++ b/arch/arm64/include/asm/cpufeature.h
>> @@ -142,7 +142,8 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
>> * capabilities and if there is a conflict, the kernel takes an action, based
>> * on the severity (e.g, a CPU could be prevented from booting or cause a
>> * kernel panic). The CPU is allowed to "affect" the state of the capability,
>> - * if it has not been finalised already.
>> + * if it has not been finalised already. See section 5 for more details on
>> + * conflicts.
>> *
>> * 4) Action: As mentioned in (2), the kernel can take an action for each detected
>> * capability, on all CPUs on the system. This is always initiated only after
>> @@ -155,6 +156,32 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
>> * b) Any late CPU, brought up after (1), the action is triggered via:
>> * check_local_cpu_capabilities() -> verify_local_cpu_capabilities()
>> *
>> + * 5) Conflicts: Based on the state of the capability on a late CPU vs. the system
>> + * state, we could have the following combinations :
>> + *
>> + * x-----------------------------x
>> + * | Type | System | Late CPU |
>> + * |-----------------------------|
>> + * | a | y | n |
>> + * |-----------------------------|
>> + * | b | n | y |
>> + * x-----------------------------x
>
> Nit: I find this a bit hard to follow. Maybe reordering things a bit
> would help but putting the rule (the precise bit) first, and the
> rationale (necessarily more vague) afterward:
>
> "Two capability type flag bits are defined to indicate whether each kind
> of conflict can be tolerated:
>
> ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU - Case (a) is allowed
> ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU - Case (b) is allowed."
>
>> + *
>> + * Case (a) is not permitted for capabilities which are usually system
>> + * features, which the system expects all CPUs to have. While (a) is ignored
>> + * for capabilities which represents an erratum work around.
>
> Similarly "Case (a) is not permitted for a capability that the system
> requires all CPUs to have in order for the capability to be enabled.
> This is typical for capabilities that represent enhanced functionality."
>
>> + *
>> + * Case (b) is not permitted for erratum capabilities, which might require
>> + * some work arounds which cannot be applied really late. Meanwhile, most
>> + * of the features could safely ignore (b), as the system doesn't use it
>> + * anyway.
>
> and
>
> "Case (b) is not permitted for a capability that the system must enable
> during boot if any CPU in the system requires it in order to run safely.
> This is typical for erratum workarounds that cannot be enabled after the
> corresponding capability is finalised.
>
> In some non-typical cases, either both (a) and (b), or neither, should
> be permitted. This can be described by including neither or both flags
> in the capability's type field."
>
> [...]
>
>>
>>
>> @@ -165,6 +192,26 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
>> #define SCOPE_SYSTEM ARM64_CPUCAP_SCOPE_SYSTEM
>> #define SCOPE_LOCAL_CPU ARM64_CPUCAP_SCOPE_LOCAL_CPU
>>
>> +/* Is it permitted for a late CPU to have this capability when system doesn't already have */
>
> "doesn't already have" -> "hasn't already enabled it"?
>
>> +#define ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU ((u16)BIT(4))
>> +/* Is it safe for a late CPU to miss this capability when system has it */
>> +#define ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU ((u16)BIT(5))
>> +
>> +/*
>> + * CPU errata detected at boot time based on feature of one or more CPUs.
>> + * It is not safe for a late CPU to have this feature when the system doesn't
>
> Can we around using the word "feature" to describe errata here?
>
> Maybe "CPU errata workarounds that need to be enabled at boot time if
> one or more CPUs in the system requires the workaround. When one of
> these workaround capabilities has been enabled, it is safe to allow any
> CPU to boot that does not require the workaround."
>
>> + * have it. But it is safe to miss the feature if the system has it.
>> + */
>> +#define ARM64_CPUCAP_LOCAL_CPU_ERRATUM \
>> + (ARM64_CPUCAP_SCOPE_LOCAL_CPU | ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU)
>> +/*
>> + * CPU feature detected at boot time based on system-wide value of a feature.
>> + * It is safe for a late CPU to have this feature even though the system doesn't
>> + * have it already. But the CPU must have this feature if the system does.
>
> "hasn't enabled it, although the feature will not be used by Linux
> in this case. If the system has enabled this feature already then every
> late CPU must have it."
>
>> + */
>> +#define ARM64_CPUCAP_SYSTEM_FEATURE \
>> + (ARM64_CPUCAP_SCOPE_SYSTEM | ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU)
>> +
>> struct arm64_cpu_capabilities {
>> const char *desc;
>> u16 capability;
>> @@ -198,6 +245,18 @@ static inline int cpucap_default_scope(const struct arm64_cpu_capabilities *cap)
>> return cap->type & ARM64_CPUCAP_SCOPE_MASK;
>> }
>>
>> +static inline bool
>> +cpucap_late_cpu_optional(const struct arm64_cpu_capabilities *cap)
>> +{
>> + return !!(cap->type & ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU);
>> +}
>> +
>> +static inline bool
>> +cpucap_late_cpu_permitted(const struct arm64_cpu_capabilities *cap)
>> +{
>> + return !!(cap->type & ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU);
>> +}
>> +
>> extern DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);
>> extern struct static_key_false cpu_hwcap_keys[ARM64_NCAPS];
>> extern struct static_key_false arm64_const_caps_ready;
>> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
>> index 328c5a031e45..22ec3960a0c5 100644
>> --- a/arch/arm64/kernel/cpu_errata.c
>> +++ b/arch/arm64/kernel/cpu_errata.c
>> @@ -175,14 +175,14 @@ static void qcom_enable_link_stack_sanitization(
>> #endif /* CONFIG_HARDEN_BRANCH_PREDICTOR */
>>
>> #define MIDR_RANGE(model, min, max) \
>> - .type = ARM64_CPUCAP_SCOPE_LOCAL_CPU, \
>> + .type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM, \
>> .matches = is_affected_midr_range, \
>> .midr_model = model, \
>> .midr_range_min = min, \
>> .midr_range_max = max
>>
>> #define MIDR_ALL_VERSIONS(model) \
>> - .type = ARM64_CPUCAP_SCOPE_LOCAL_CPU, \
>> + .type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM, \
>> .matches = is_affected_midr_range, \
>> .midr_model = model, \
>> .midr_range_min = 0, \
>> @@ -286,7 +286,7 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
>> .desc = "Mismatched cache line size",
>> .capability = ARM64_MISMATCHED_CACHE_LINE_SIZE,
>> .matches = has_mismatched_cache_line_size,
>> - .type = ARM64_CPUCAP_SCOPE_LOCAL_CPU,
>> + .type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM,
>> .cpu_enable = cpu_enable_trap_ctr_access,
>> },
>> #ifdef CONFIG_QCOM_FALKOR_ERRATUM_1003
>> @@ -300,7 +300,7 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
>> {
>> .desc = "Qualcomm Technologies Kryo erratum 1003",
>> .capability = ARM64_WORKAROUND_QCOM_FALKOR_E1003,
>> - .type = ARM64_CPUCAP_SCOPE_LOCAL_CPU,
>> + .type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM,
>> .midr_model = MIDR_QCOM_KRYO,
>> .matches = is_kryo_midr,
>> },
>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
>> index 8d22f0ef0927..1b29b3f0a1bc 100644
>> --- a/arch/arm64/kernel/cpufeature.c
>> +++ b/arch/arm64/kernel/cpufeature.c
>> @@ -921,7 +921,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>> {
>> .desc = "GIC system register CPU interface",
>> .capability = ARM64_HAS_SYSREG_GIC_CPUIF,
>> - .type = ARM64_CPUCAP_SCOPE_SYSTEM,
>> + .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>> .matches = has_useable_gicv3_cpuif,
>> .sys_reg = SYS_ID_AA64PFR0_EL1,
>> .field_pos = ID_AA64PFR0_GIC_SHIFT,
>> @@ -932,7 +932,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>> {
>> .desc = "Privileged Access Never",
>> .capability = ARM64_HAS_PAN,
>> - .type = ARM64_CPUCAP_SCOPE_SYSTEM,
>> + .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>> .matches = has_cpuid_feature,
>> .sys_reg = SYS_ID_AA64MMFR1_EL1,
>> .field_pos = ID_AA64MMFR1_PAN_SHIFT,
>> @@ -945,7 +945,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>> {
>> .desc = "LSE atomic instructions",
>> .capability = ARM64_HAS_LSE_ATOMICS,
>> - .type = ARM64_CPUCAP_SCOPE_SYSTEM,
>> + .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>> .matches = has_cpuid_feature,
>> .sys_reg = SYS_ID_AA64ISAR0_EL1,
>> .field_pos = ID_AA64ISAR0_ATOMICS_SHIFT,
>> @@ -956,14 +956,14 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>> {
>> .desc = "Software prefetching using PRFM",
>> .capability = ARM64_HAS_NO_HW_PREFETCH,
>> - .type = ARM64_CPUCAP_SCOPE_SYSTEM,
>> + .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>> .matches = has_no_hw_prefetch,
>> },
>> #ifdef CONFIG_ARM64_UAO
>> {
>> .desc = "User Access Override",
>> .capability = ARM64_HAS_UAO,
>> - .type = ARM64_CPUCAP_SCOPE_SYSTEM,
>> + .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>> .matches = has_cpuid_feature,
>> .sys_reg = SYS_ID_AA64MMFR2_EL1,
>> .field_pos = ID_AA64MMFR2_UAO_SHIFT,
>> @@ -977,21 +977,21 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>> #ifdef CONFIG_ARM64_PAN
>> {
>> .capability = ARM64_ALT_PAN_NOT_UAO,
>> - .type = ARM64_CPUCAP_SCOPE_SYSTEM,
>> + .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>> .matches = cpufeature_pan_not_uao,
>> },
>> #endif /* CONFIG_ARM64_PAN */
>> {
>> .desc = "Virtualization Host Extensions",
>> .capability = ARM64_HAS_VIRT_HOST_EXTN,
>> - .type = ARM64_CPUCAP_SCOPE_SYSTEM,
>> + .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>> .matches = runs_at_el2,
>> .cpu_enable = cpu_copy_el2regs,
>> },
>> {
>> .desc = "32-bit EL0 Support",
>> .capability = ARM64_HAS_32BIT_EL0,
>> - .type = ARM64_CPUCAP_SCOPE_SYSTEM,
>> + .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>> .matches = has_cpuid_feature,
>> .sys_reg = SYS_ID_AA64PFR0_EL1,
>> .sign = FTR_UNSIGNED,
>> @@ -1001,21 +1001,21 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>> {
>> .desc = "Reduced HYP mapping offset",
>> .capability = ARM64_HYP_OFFSET_LOW,
>> - .type = ARM64_CPUCAP_SCOPE_SYSTEM,
>> + .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>> .matches = hyp_offset_low,
>> },
>> #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
>> {
>> .desc = "Kernel page table isolation (KPTI)",
>> .capability = ARM64_UNMAP_KERNEL_AT_EL0,
>> - .type = ARM64_CPUCAP_SCOPE_SYSTEM,
>> + .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>> .matches = unmap_kernel_at_el0,
>> },
>> #endif
>> {
>> /* FP/SIMD is not implemented */
>> .capability = ARM64_HAS_NO_FPSIMD,
>> - .type = ARM64_CPUCAP_SCOPE_SYSTEM,
>> + .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>> .min_field_value = 0,
>> .matches = has_no_fpsimd,
>> },
>> @@ -1023,7 +1023,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>> {
>> .desc = "Data cache clean to Point of Persistence",
>> .capability = ARM64_HAS_DCPOP,
>> - .type = ARM64_CPUCAP_SCOPE_SYSTEM,
>> + .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>> .matches = has_cpuid_feature,
>> .sys_reg = SYS_ID_AA64ISAR1_EL1,
>> .field_pos = ID_AA64ISAR1_DPB_SHIFT,
>> @@ -1033,7 +1033,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>> #ifdef CONFIG_ARM64_SVE
>> {
>> .desc = "Scalable Vector Extension",
>> - .type = ARM64_CPUCAP_SCOPE_SYSTEM,
>> + .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>> .capability = ARM64_SVE,
>> .sys_reg = SYS_ID_AA64PFR0_EL1,
>> .sign = FTR_UNSIGNED,
>> @@ -1047,7 +1047,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>> {
>> .desc = "RAS Extension Support",
>> .capability = ARM64_HAS_RAS_EXTN,
>> - .type = ARM64_CPUCAP_SCOPE_SYSTEM,
>> + .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>> .matches = has_cpuid_feature,
>> .sys_reg = SYS_ID_AA64PFR0_EL1,
>> .sign = FTR_UNSIGNED,
>> @@ -1062,7 +1062,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>> #define HWCAP_CAP(reg, field, s, min_value, cap_type, cap) \
>> { \
>> .desc = #cap, \
>> - .type = ARM64_CPUCAP_SCOPE_SYSTEM, \
>> + .type = ARM64_CPUCAP_SYSTEM_FEATURE, \
>> .matches = has_cpuid_feature, \
>> .sys_reg = reg, \
>> .field_pos = field, \
>> --
>> 2.14.3
>>
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>

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