On Fri, Feb 09, 2018 at 05:54:57PM +0000, Suzuki K Poulose wrote: > The kernel detects and uses some of the features based on the boot > CPU and expects that all the following CPUs conform to it. e.g, > with VHE and the boot CPU running at EL2, the kernel decides to > keep the kernel running at EL2. If another CPU is brought up without > this capability, we use custom hooks (via check_early_cpu_features()) > to handle it. To handle such capabilities add support for detecting > and enabling capabilities based on the boot CPU. > > A bit is added to indicate if the capability should be detected > early on the boot CPU. The infrastructure then ensures that such > capabilities are probed and "enabled" early on in the boot CPU > and, enabled on the subsequent CPUs. > > Cc: Julien Thierry <julien.thie...@arm.com> > Cc: Dave Martin <dave.mar...@arm.com> > Cc: Will Deacon <will.dea...@arm.com> > Cc: Mark Rutland <mark.rutl...@arm.com> > Cc: Marc Zyngier <marc.zyng...@arm.com> > Signed-off-by: Suzuki K Poulose <suzuki.poul...@arm.com> > --- > arch/arm64/include/asm/cpufeature.h | 46 +++++++++++++++++++++++++++++------- > arch/arm64/kernel/cpufeature.c | 47 > +++++++++++++++++++++++++++---------- > 2 files changed, 72 insertions(+), 21 deletions(-) > > diff --git a/arch/arm64/include/asm/cpufeature.h > b/arch/arm64/include/asm/cpufeature.h > index 383c69c95f23..5f56a8342065 100644 > --- a/arch/arm64/include/asm/cpufeature.h > +++ b/arch/arm64/include/asm/cpufeature.h > @@ -104,7 +104,7 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0; > * some checks at runtime. This could be, e.g, checking the value of a > field > * in CPU ID feature register or checking the cpu model. The capability > * provides a call back ( @matches() ) to perform the check. > - * Scope defines how the checks should be performed. There are two cases: > + * Scope defines how the checks should be performed. There are three > cases: > * > * a) SCOPE_LOCAL_CPU: check all the CPUs and "detect" if at least one > * matches. This implies, we have to run the check on all the booting > @@ -117,6 +117,11 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0; > * field in one of the CPU ID feature registers, we use the sanitised > * value of the register from the CPU feature infrastructure to make > * the decision. > + * Or > + * c) SCOPE_BOOT_CPU: Check only on the primary boot CPU to detect the > feature. > + * This category is for features that are "finalised" (or used) by > the kernel > + * very early even before the SMP cpus are brought up. > + *
Nit: the overlong lines bring no benefit here. Please wrap them if possible -- but to avoid patch churn only bother for lines actually changed/added by this patch. > * The process of detection is usually denoted by "update" capability > state > * in the code. > * > @@ -133,6 +138,11 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0; > * w.r.t the capability. e.g, all secondary CPUs are treated "late CPUs" > for > * capabilities determined by the boot CPU. > * > + * At the moment there are two passes of finalising the capabilities. > + * a) Boot CPU scope capabilities - Finalised by primary boot CPU via > + * setup_boot_cpu_capabilities(). > + * b) Everything except (a) - Run via setup_system_capabilities(). > + * > * 3) Verification: When a CPU is brought online (e.g, by user or by the > kernel), > * the kernel should make sure that it is safe to use the CPU, by > verifying > * that the CPU is compliant with the state of the capabilities finalised > @@ -141,12 +151,19 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0; > * secondary_start_kernel()-> check_local_cpu_capabilities() > * > * As explained in (2) above, capabilities could be finalised at different > - * points in the execution. Each CPU is verified against the "finalised" > - * 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. See section 5 for more details on > - * conflicts. > + * points in the execution. Each newly booted CPU is verified against > those > + * capabilities that have been finalised by the time it boots. > + * > + * a) SCOPE_BOOT_CPU : All CPUs are verified against the capability except > + * for the primary boot CPU. > + * > + * b) SCOPE_LOCAL_CPU, SCOPE_SYSTEM: All CPUs hotplugged on by the user > + * after the kernel boot are verified against the capability. > + * > + * 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. 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. Appropriate actions include, > turning > @@ -193,15 +210,26 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0; > */ > > > -/* Decide how the capability is detected. On a local CPU vs System wide */ > +/* > + * Decide how the capability is detected. > + * On any local CPU vs System wide vs the primary boot CPU > + */ > #define ARM64_CPUCAP_SCOPE_LOCAL_CPU ((u16)BIT(0)) > #define ARM64_CPUCAP_SCOPE_SYSTEM ((u16)BIT(1)) > +/* > + * The capabilitiy is detected on the Boot CPU and is used by kernel > + * during early boot. i.e, the capability should be "detected" and "enabled" > + * as early as possibly on all booting CPUs. > + */ > +#define ARM64_CPUCAP_SCOPE_BOOT_CPU ((u16)BIT(2)) > #define ARM64_CPUCAP_SCOPE_MASK \ > (ARM64_CPUCAP_SCOPE_SYSTEM | \ > - ARM64_CPUCAP_SCOPE_LOCAL_CPU) > + ARM64_CPUCAP_SCOPE_LOCAL_CPU | \ > + ARM64_CPUCAP_SCOPE_BOOT_CPU) > > #define SCOPE_SYSTEM ARM64_CPUCAP_SCOPE_SYSTEM > #define SCOPE_LOCAL_CPU > ARM64_CPUCAP_SCOPE_LOCAL_CPU > +#define SCOPE_BOOT_CPU > ARM64_CPUCAP_SCOPE_BOOT_CPU > #define SCOPE_ALL ARM64_CPUCAP_SCOPE_MASK > > /* > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index a15be4db6bf4..7625e2962e2b 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -504,7 +504,7 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, u64 new) > } > > extern const struct arm64_cpu_capabilities arm64_errata[]; > -static void update_cpu_capabilities(u16 scope_mask); > +static void __init setup_boot_cpu_capabilities(void); > > void __init init_cpu_features(struct cpuinfo_arm64 *info) > { > @@ -550,10 +550,10 @@ void __init init_cpu_features(struct cpuinfo_arm64 > *info) > } > > /* > - * Run the errata work around and local feature checks on the > - * boot CPU, once we have initialised the cpu feature infrastructure. > + * Detect and enable early CPU capabilities based on the boot CPU, > + * after we have initialised the CPU feature infrastructure. > */ > - update_cpu_capabilities(SCOPE_LOCAL_CPU); > + setup_boot_cpu_capabilities(); > } > > static void update_cpu_ftr_reg(struct arm64_ftr_reg *reg, u64 new) > @@ -1277,12 +1277,21 @@ __enable_cpu_capabilities(const struct > arm64_cpu_capabilities *caps, u16 scope_m > > if (caps->cpu_enable) { > /* > - * Use stop_machine() as it schedules the work allowing > - * us to modify PSTATE, instead of on_each_cpu() which > - * uses an IPI, giving us a PSTATE that disappears when > - * we return. > + * If we are dealing with a boot CPU capability, we > + * have to enable this only on the Boot CPU, where it > + * is detected. All the secondaries enable it via > + * check_local_cpu_capabilities(). I found this confusing to read, because it's not 100% clear whether the "If we are dealing with a boot CPU capability" applies to the second sentence as well. Maybe this would be clearer as: "Capabilities with SCOPE_BOOT_CPU are finalised before any secondary CPU boots. Thus, each secondary will enable the capability as appropriate via check_local_cpu_capabilities(). The only exception is the boot CPU, for which the capability must be enabled here. This approach avoids costly stop_machine() calls for this case." Thoughts? > + * > + * Otherwise, use stop_machine() as it schedules the > + * work allowing us to modify PSTATE, instead of > + * on_each_cpu() which uses an IPI, giving us a PSTATE > + * that disappears when we return. > */ > - stop_machine(__enable_cpu_capability, (void *)caps, > cpu_online_mask); > + if (scope_mask & SCOPE_BOOT_CPU) > + caps->cpu_enable(caps); > + else > + stop_machine(__enable_cpu_capability, > + (void *)caps, cpu_online_mask); > } > } > } > @@ -1362,6 +1371,12 @@ static void check_early_cpu_features(void) > { > verify_cpu_run_el(); > verify_cpu_asid_bits(); > + /* > + * Early features are used by the kernel already. If there > + * is a conflict, we cannot proceed further. > + */ > + if (!verify_local_cpu_caps(SCOPE_BOOT_CPU)) > + cpu_panic_kernel(); > } > > static void > @@ -1403,9 +1418,8 @@ static void verify_sve_features(void) > */ > static void verify_local_cpu_capabilities(void) > { Nit: Maybe add a comment saying where SCOPE_BOOT_CPU capabilities are checked. > - if (!verify_local_cpu_caps(SCOPE_ALL)) > + if (!verify_local_cpu_caps(SCOPE_ALL & ~SCOPE_BOOT_CPU)) > cpu_die_early(); > - Nit: keep blank line? Otherwise it looks like the if() falls through, where really cpu_die_early() does not return. > verify_local_elf_hwcaps(arm64_elf_hwcaps); > > if (system_supports_32bit_el0()) > @@ -1438,6 +1452,14 @@ void check_local_cpu_capabilities(void) > verify_local_cpu_capabilities(); > } > > +static void __init setup_boot_cpu_capabilities(void) > +{ > + /* Detect capabilities with either SCOPE_BOOT_CPU or SCOPE_LOCAL_CPU */ > + update_cpu_capabilities(SCOPE_BOOT_CPU | SCOPE_LOCAL_CPU); > + /* Enable the SCOPE_BOOT_CPU capabilities alone right away */ > + enable_cpu_capabilities(SCOPE_BOOT_CPU); > +} > + > DEFINE_STATIC_KEY_FALSE(arm64_const_caps_ready); > EXPORT_SYMBOL(arm64_const_caps_ready); > > @@ -1462,7 +1484,8 @@ static void __init setup_system_capabilities(void) > * on it. Also enable all the available capabilities. > */ > update_cpu_capabilities(SCOPE_SYSTEM); > - enable_cpu_capabilities(SCOPE_ALL); > + /* Enable all the available capabilities, which are not already > enabled. */ > + enable_cpu_capabilities(SCOPE_ALL & ~SCOPE_BOOT_CPU); > } > > void __init setup_cpu_features(void) > -- > 2.14.3 With fair consideration given to the nits above: Reviewed-by: Dave Martin <dave.mar...@arm.com>