Messages in this thread |  | | Subject | Re: [PATCH v2 2/6] arm64: alternative: Apply alternatives early in boot process | From | Julien Thierry <> | Date | Fri, 4 May 2018 11:06:56 +0100 |
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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. > > Introduce apply_alternatives_early() to allow some alternatives to be > applied immediately after we detect the CPU features of the boot CPU. > > Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org> > Signed-off-by: Julien Thierry <julien.thierry@arm.com> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will.deacon@arm.com> > --- > arch/arm64/include/asm/alternative.h | 1 + > arch/arm64/kernel/alternative.c | 39 +++++++++++++++++++++++++++++++++--- > arch/arm64/kernel/smp.c | 6 ++++++ > 3 files changed, 43 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h > index 4a85c69..1fc1cdb 100644 > --- a/arch/arm64/include/asm/alternative.h > +++ b/arch/arm64/include/asm/alternative.h > @@ -20,6 +20,7 @@ struct alt_instr { > u8 alt_len; /* size of new instruction(s), <= orig_len */ > }; > > +void __init apply_alternatives_early(void); > void __init apply_alternatives_all(void); > void apply_alternatives(void *start, size_t length); > > diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c > index 6dd0a3a3..78051d4 100644 > --- a/arch/arm64/kernel/alternative.c > +++ b/arch/arm64/kernel/alternative.c > @@ -28,6 +28,18 @@ > #include <asm/sections.h> > #include <linux/stop_machine.h> > > +/* > + * 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.
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.
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).
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
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