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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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