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    SubjectRe: [PATCH v8 15/26] arm64: alternative: Apply alternatives early in boot process
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    Hi Julien,

    On 08/01/2019 14:07, 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_boot_alternatives() 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>
    > [julien.thierry@arm.com: rename to fit new cpufeature framework better,
    > apply BOOT_SCOPE feature early in boot]
    > Signed-off-by: Julien Thierry <julien.thierry@arm.com>
    > Cc: Catalin Marinas <catalin.marinas@arm.com>
    > Cc: Will Deacon <will.deacon@arm.com>
    > Cc: Christoffer Dall <christoffer.dall@arm.com>
    > Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
    > ---
    > arch/arm64/include/asm/alternative.h | 1 +
    > arch/arm64/include/asm/cpufeature.h | 4 ++++
    > arch/arm64/kernel/alternative.c | 43 +++++++++++++++++++++++++++++++-----
    > arch/arm64/kernel/cpufeature.c | 6 +++++
    > arch/arm64/kernel/smp.c | 7 ++++++
    > 5 files changed, 56 insertions(+), 5 deletions(-)
    >
    > diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h
    > index 9806a23..b9f8d78 100644
    > --- a/arch/arm64/include/asm/alternative.h
    > +++ b/arch/arm64/include/asm/alternative.h
    > @@ -25,6 +25,7 @@ struct alt_instr {
    > typedef void (*alternative_cb_t)(struct alt_instr *alt,
    > __le32 *origptr, __le32 *updptr, int nr_inst);
    >
    > +void __init apply_boot_alternatives(void);
    > void __init apply_alternatives_all(void);
    > bool alternative_is_applied(u16 cpufeature);
    >
    > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
    > index 89c3f31..e505e1f 100644
    > --- a/arch/arm64/include/asm/cpufeature.h
    > +++ b/arch/arm64/include/asm/cpufeature.h
    > @@ -391,6 +391,10 @@ static inline int cpucap_default_scope(const struct arm64_cpu_capabilities *cap)
    > extern struct static_key_false cpu_hwcap_keys[ARM64_NCAPS];
    > extern struct static_key_false arm64_const_caps_ready;
    >
    > +/* ARM64 CAPS + alternative_cb */
    > +#define ARM64_NPATCHABLE (ARM64_NCAPS + 1)
    > +extern DECLARE_BITMAP(boot_capabilities, ARM64_NPATCHABLE);
    > +
    > #define for_each_available_cap(cap) \
    > for_each_set_bit(cap, cpu_hwcaps, ARM64_NCAPS)
    >
    > diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c
    > index c947d22..a9b4677 100644
    > --- a/arch/arm64/kernel/alternative.c
    > +++ b/arch/arm64/kernel/alternative.c
    > @@ -155,7 +155,8 @@ static void clean_dcache_range_nopatch(u64 start, u64 end)
    > } while (cur += d_size, cur < end);
    > }
    >
    > -static void __apply_alternatives(void *alt_region, bool is_module)
    > +static void __apply_alternatives(void *alt_region, bool is_module,
    > + unsigned long *feature_mask)
    > {
    > struct alt_instr *alt;
    > struct alt_region *region = alt_region;
    > @@ -165,6 +166,9 @@ static void __apply_alternatives(void *alt_region, bool is_module)
    > for (alt = region->begin; alt < region->end; alt++) {
    > int nr_inst;
    >
    > + if (!test_bit(alt->cpufeature, feature_mask))
    > + continue;
    > +
    > /* Use ARM64_CB_PATCH as an unconditional patch */
    > if (alt->cpufeature < ARM64_CB_PATCH &&
    > !cpus_have_cap(alt->cpufeature))
    > @@ -203,8 +207,11 @@ static void __apply_alternatives(void *alt_region, bool is_module)
    > __flush_icache_all();
    > isb();
    >
    > - /* We applied all that was available */
    > - bitmap_copy(applied_alternatives, cpu_hwcaps, ARM64_NCAPS);
    > + /* Ignore ARM64_CB bit from feature mask */
    > + bitmap_or(applied_alternatives, applied_alternatives,
    > + feature_mask, ARM64_NCAPS);
    > + bitmap_and(applied_alternatives, applied_alternatives,
    > + cpu_hwcaps, ARM64_NCAPS);
    > }
    > }
    >
    > @@ -225,8 +232,13 @@ static int __apply_alternatives_multi_stop(void *unused)
    > cpu_relax();
    > isb();
    > } else {
    > + DECLARE_BITMAP(remaining_capabilities, ARM64_NPATCHABLE);
    > +
    > + bitmap_complement(remaining_capabilities, boot_capabilities,
    > + ARM64_NPATCHABLE);
    > +
    > BUG_ON(all_alternatives_applied);
    > - __apply_alternatives(&region, false);
    > + __apply_alternatives(&region, false, remaining_capabilities);
    > /* Barriers provided by the cache flushing */
    > WRITE_ONCE(all_alternatives_applied, 1);
    > }
    > @@ -240,6 +252,24 @@ void __init apply_alternatives_all(void)
    > stop_machine(__apply_alternatives_multi_stop, NULL, cpu_online_mask);
    > }
    >
    > +/*
    > + * 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 __init apply_boot_alternatives(void)
    > +{
    > + struct alt_region region = {
    > + .begin = (struct alt_instr *)__alt_instructions,
    > + .end = (struct alt_instr *)__alt_instructions_end,
    > + };
    > +
    > + /* If called on non-boot cpu things could go wrong */
    > + WARN_ON(smp_processor_id() != 0);
    > +
    > + __apply_alternatives(&region, false, &boot_capabilities[0]);
    > +}
    > +
    > #ifdef CONFIG_MODULES
    > void apply_alternatives_module(void *start, size_t length)
    > {
    > @@ -247,7 +277,10 @@ void apply_alternatives_module(void *start, size_t length)
    > .begin = start,
    > .end = start + length,
    > };
    > + DECLARE_BITMAP(all_capabilities, ARM64_NPATCHABLE);
    > +
    > + bitmap_fill(all_capabilities, ARM64_NPATCHABLE);
    >
    > - __apply_alternatives(&region, true);
    > + __apply_alternatives(&region, true, &all_capabilities[0]);
    > }
    > #endif
    > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
    > index 84fa5be..71c8d4f 100644
    > --- a/arch/arm64/kernel/cpufeature.c
    > +++ b/arch/arm64/kernel/cpufeature.c
    > @@ -54,6 +54,9 @@
    > EXPORT_SYMBOL(cpu_hwcaps);
    > static struct arm64_cpu_capabilities const __ro_after_init *cpu_hwcaps_ptrs[ARM64_NCAPS];
    >
    > +/* Need also bit for ARM64_CB_PATCH */
    > +DECLARE_BITMAP(boot_capabilities, ARM64_NPATCHABLE);
    > +
    > /*
    > * Flag to indicate if we have computed the system wide
    > * capabilities based on the boot time active CPUs. This
    > @@ -1672,6 +1675,9 @@ static void update_cpu_capabilities(u16 scope_mask)
    > if (caps->desc)
    > pr_info("detected: %s\n", caps->desc);
    > cpus_set_cap(caps->capability);
    > +
    > + if (caps->type & SCOPE_BOOT_CPU)

    You may want to do :
    if (scope_mask & SCOPE_BOOT_CPU)

    for a tighter check to ensure this doesn't update the boot_capabilities
    after we have applied the boot_scope alternatives and miss applying the
    alternatives for those, should someone add a multi-scope (i.e SCOPE_BOOT_CPU and
    something else) capability (even by mistake).

    With that:

    Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>

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