Messages in this thread Patch in this message |  | | Subject | Re: [PATCH v2 2/6] arm64: alternative: Apply alternatives early in boot process | From | Suzuki K Poulose <> | Date | Wed, 9 May 2018 22:52:21 +0100 |
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On 05/04/2018 11:06 AM, Julien Thierry wrote: > Hi, > > In order to prepare the v3 of this patchset, I'd like people's opinion > on what this patch does. More below. > > On 17/01/18 11:54, Julien Thierry wrote: >> From: Daniel Thompson <daniel.thompson@linaro.org> >> >> Currently alternatives are applied very late in the boot process (and >> a long time after we enable scheduling). Some alternative sequences, >> such as those that alter the way CPU context is stored, must be applied >> much earlier in the boot sequence.
>> +/* >> + * early-apply features are detected using only the boot CPU and >> checked on >> + * secondary CPUs startup, even then, >> + * These early-apply features should only include features where we must >> + * patch the kernel very early in the boot process. >> + * >> + * Note that the cpufeature logic *must* be made aware of early-apply >> + * features to ensure they are reported as enabled without waiting >> + * for other CPUs to boot. >> + */ >> +#define EARLY_APPLY_FEATURE_MASK BIT(ARM64_HAS_SYSREG_GIC_CPUIF) >> + > > Following the change in the cpufeature infrastructure, > ARM64_HAS_SYSREG_GIC_CPUIF will have the scope > ARM64_CPUCAP_SCOPE_BOOT_CPU in order to be checked early in the boot > process.
Thats correct.
> > Now, regarding the early application of alternative, I am wondering > whether we can apply all the alternatives associated with SCOPE_BOOT > features that *do not* have a cpu_enable callback. >
I don't understand why would you skip the ones that have a "cpu_enable" callback. Could you explain this a bit ? Ideally you should be able to apply the alternatives for features with the SCOPE_BOOT, provided the cpu_enable() callback is written properly.
> Otherwise we can keep the macro to list individually each feature that > is patchable at boot time as the current patch does (or put this info in > a flag within the arm64_cpu_capabilities structure)
You may be able to build up the mask of *available* capabilities with SCOPE_BOOT at boot time by playing some trick in the setup_boot_cpu_capabilities(), rather than embedding it in the capabilities (and then parsing the entire table(s)) or manually keeping track of the capabilities by having a separate mask.
Suzuki
> > Any thoughts or preferences on this? > > Thanks, > >> #define __ALT_PTR(a,f) ((void *)&(a)->f + (a)->f) >> #define ALT_ORIG_PTR(a) __ALT_PTR(a, orig_offset) >> #define ALT_REPL_PTR(a) __ALT_PTR(a, alt_offset) >> @@ -105,7 +117,8 @@ static u32 get_alt_insn(struct alt_instr *alt, >> __le32 *insnptr, __le32 *altinsnp >> return insn; >> } >> >> -static void __apply_alternatives(void *alt_region, bool >> use_linear_alias) >> +static void __apply_alternatives(void *alt_region, bool >> use_linear_alias, >> + unsigned long feature_mask) >> { >> struct alt_instr *alt; >> struct alt_region *region = alt_region; >> @@ -115,6 +128,9 @@ static void __apply_alternatives(void *alt_region, >> bool use_linear_alias) >> u32 insn; >> int i, nr_inst; >> >> + if ((BIT(alt->cpufeature) & feature_mask) == 0) >> + continue; >> + >> if (!cpus_have_cap(alt->cpufeature)) >> continue; >> >> @@ -138,6 +154,21 @@ static void __apply_alternatives(void >> *alt_region, bool use_linear_alias) >> } >> >> /* >> + * This is called very early in the boot process (directly after we run >> + * a feature detect on the boot CPU). No need to worry about other CPUs >> + * here. >> + */ >> +void apply_alternatives_early(void) >> +{ >> + struct alt_region region = { >> + .begin = (struct alt_instr *)__alt_instructions, >> + .end = (struct alt_instr *)__alt_instructions_end, >> + }; >> + >> + __apply_alternatives(®ion, true, EARLY_APPLY_FEATURE_MASK); >> +} >> + >> +/* >> * We might be patching the stop_machine state machine, so implement a >> * really simple polling protocol here. >> */ >> @@ -156,7 +187,9 @@ static int __apply_alternatives_multi_stop(void >> *unused) >> isb(); >> } else { >> BUG_ON(patched); >> - __apply_alternatives(®ion, true); >> + >> + __apply_alternatives(®ion, true, ~EARLY_APPLY_FEATURE_MASK); >> + >> /* Barriers provided by the cache flushing */ >> WRITE_ONCE(patched, 1); >> } >> @@ -177,5 +210,5 @@ void apply_alternatives(void *start, size_t length) >> .end = start + length, >> }; >> >> - __apply_alternatives(®ion, false); >> + __apply_alternatives(®ion, false, -1); >> } >> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c >> index 551eb07..37361b5 100644 >> --- a/arch/arm64/kernel/smp.c >> +++ b/arch/arm64/kernel/smp.c >> @@ -453,6 +453,12 @@ void __init smp_prepare_boot_cpu(void) >> * cpuinfo_store_boot_cpu() above. >> */ >> update_cpu_errata_workarounds(); >> + /* >> + * We now know enough about the boot CPU to apply the >> + * alternatives that cannot wait until interrupt handling >> + * and/or scheduling is enabled. >> + */ >> + apply_alternatives_early(); >> } >> >> static u64 __init of_get_cpu_mpidr(struct device_node *dn) >> -- >> 1.9.1 >> >
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