Messages in this thread |  | | From | Julien Thierry <> | Subject | Re: [PATCH v2 2/6] arm64: alternative: Apply alternatives early in boot process | Date | Fri, 11 May 2018 09:12:59 +0100 |
| |
On 09/05/18 22:52, Suzuki K Poulose wrote: > 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. >
In my mind the "cpu_enable" callback is the setup a cpu should perform before using the feature (i.e. the code getting patched in by the alternative). So I was worried about the code getting patched by the boot cpu and then have the secondary cpus ending up executing patched code before the cpu_enable for the corresponding feature gets called. Or is there a requirement for secondary cpu startup code to be free of alternative code?
> >> 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. >
Yes, I like that idea.
Thanks,
> 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 >>> >> >
-- Julien Thierry
|  |