From: Julien Thierry <julien.thierry@arm.com>
To: Suzuki K Poulose <suzuki.poulose@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Cc: mark.rutland@arm.com, marc.zyngier@arm.com, james.morse@arm.com,
daniel.thompson@linaro.org,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH v2 2/6] arm64: alternative: Apply alternatives early in boot process
Date: Fri, 11 May 2018 09:12:59 +0100 [thread overview]
Message-ID: <d170336d-8af0-893a-acb2-51900c28ade5@arm.com> (raw)
In-Reply-To: <7a3afa42-821a-3d4a-3af8-00ba18653a4a@arm.com>
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
next prev parent reply other threads:[~2018-05-11 8:13 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-17 11:54 [PATCH v2 0/6] arm64: provide pseudo NMI with GICv3 Julien Thierry
2018-01-17 11:54 ` [PATCH v2 1/6] arm64: cpufeature: Allow early detect of specific features Julien Thierry
2018-01-22 12:05 ` Suzuki K Poulose
2018-01-22 12:21 ` Julien Thierry
2018-01-22 13:38 ` Daniel Thompson
2018-01-22 13:57 ` Marc Zyngier
2018-01-22 14:14 ` Julien Thierry
2018-01-22 14:20 ` Marc Zyngier
2018-01-22 14:45 ` Suzuki K Poulose
2018-01-22 15:01 ` Julien Thierry
2018-01-22 15:13 ` Suzuki K Poulose
2018-01-22 15:23 ` Julien Thierry
2018-01-22 15:34 ` Suzuki K Poulose
2018-01-17 11:54 ` [PATCH v2 2/6] arm64: alternative: Apply alternatives early in boot process Julien Thierry
2018-05-04 10:06 ` Julien Thierry
2018-05-09 14:27 ` Daniel Thompson
2018-05-09 21:52 ` Suzuki K Poulose
2018-05-11 8:12 ` Julien Thierry [this message]
2018-05-11 9:19 ` Suzuki K Poulose
2018-01-17 11:54 ` [PATCH v2 3/6] arm64: irqflags: Use ICC sysregs to implement IRQ masking Julien Thierry
2018-01-17 11:54 ` [PATCH v2 4/6] irqchip/gic: Add functions to access irq priorities Julien Thierry
2018-01-17 11:54 ` [PATCH v2 5/6] arm64: Detect current view of GIC priorities Julien Thierry
2018-02-03 3:01 ` Yang Yingliang
2018-01-17 11:54 ` [PATCH v2 6/6] arm64: Add support for pseudo-NMIs Julien Thierry
2018-01-17 12:10 ` [PATCH v2 0/6] arm64: provide pseudo NMI with GICv3 Julien Thierry
2018-04-29 6:37 ` Joel Fernandes
2018-04-30 9:53 ` Julien Thierry
2018-04-30 10:55 ` Daniel Thompson
2018-05-01 18:18 ` Joel Fernandes
2018-05-02 11:02 ` Daniel Thompson
2018-04-29 6:35 ` Joel Fernandes
2018-04-30 9:46 ` Julien Thierry
2018-05-01 20:51 ` Joel Fernandes
2018-05-02 11:08 ` Marc Zyngier
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=d170336d-8af0-893a-acb2-51900c28ade5@arm.com \
--to=julien.thierry@arm.com \
--cc=catalin.marinas@arm.com \
--cc=daniel.thompson@linaro.org \
--cc=james.morse@arm.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=marc.zyngier@arm.com \
--cc=mark.rutland@arm.com \
--cc=suzuki.poulose@arm.com \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).