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Date: Tue, 8 Jan 2019 17:40:40 +0000
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Julien Thierry <julien.thierry@....com>,
linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org, daniel.thompson@...aro.org,
joel@...lfernandes.org, marc.zyngier@....com,
christoffer.dall@....com, james.morse@....com,
catalin.marinas@....com, will.deacon@....com, mark.rutland@....com
Subject: Re: [PATCH v8 15/26] arm64: alternative: Apply alternatives early in
boot process
On 08/01/2019 15:20, Julien Thierry wrote:
> Hi Suzuki,
>
> On 08/01/2019 14:51, Suzuki K Poulose wrote:
>> Hi Julien,
>>
>> On 08/01/2019 14:07, Julien Thierry wrote:
>>> From: Daniel Thompson <daniel.thompson@...aro.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@...aro.org>
>>> [julien.thierry@....com: rename to fit new cpufeature framework better,
>>> apply BOOT_SCOPE feature early in boot]
>>> Signed-off-by: Julien Thierry <julien.thierry@....com>
>>> Cc: Catalin Marinas <catalin.marinas@....com>
>>> Cc: Will Deacon <will.deacon@....com>
>>> Cc: Christoffer Dall <christoffer.dall@....com>
>>> Cc: Suzuki K Poulose <suzuki.poulose@....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(®ion, false);
>>> + __apply_alternatives(®ion, 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(®ion, 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(®ion, true);
>>> + __apply_alternatives(®ion, 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).
>>
>
> But a multi-scope capability containing SCOPE_BOOT_CPU should already
> get updated for setup_boot_cpu_capabilities. Capabilities marked with
> SCOPE_BOOT_CPU need to be enabled on the boot CPU or not at all.
Yes, you're right. It is not normal to have multiple SCOPE for a "capability".
But if someone comes with such a cap, we may miss handling this case. It is
always better to be safer.
>
> Shouldn't the call to caps->matches() fail for a boot feature that was
> not found on the boot cpu?
>
> Also, you made the opposite suggestion 4 version ago with a more
> worrying scenario :) :
> https://lkml.org/lkml/2018/5/25/208
Ah, you're right. I missed that. We need the additional check as you mention
below.
>
> Otherwise, if my assumption above is wrong, it means the check should
> probably be:
> if (caps->type & SCOPE_BOOT_CPU && scope_mask & SCOPE_BOOT_CPU)
Yes, this is what we want.
> But my current understanding is that we don't need that.
>
>> With that:
>>
>> Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>
Cheers
Suzuki
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