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SubjectRe: [PATCH 1/2] arm64: capabilities: Allow flexibility in scope
On Thu, Feb 08, 2018 at 12:12:37PM +0000, Suzuki K Poulose wrote:
> So far we have restricted the scopes for the capabilities
> as follows :
> 1) Errata workaround check are run all CPUs (i.e, always
> SCOPE_LOCAL_CPU)
> 2) Arm64 features are run only once after the sanitised
> feature registers are available using the SCOPE_SYSTEM.
>
> This prevents detecting cpu features that can be detected
> on one or more CPUs with SCOPE_LOCAL_CPU (e.g KPTI). Similarly
> for errata workaround with SCOPE_SYSTEM.
>
> This patch makes sure that we allow flexibility of having
> any scope for a capability. So, we now run through both
> arm64_features and arm64_errata in two phases for detection:
>
> a) with SCOPE_LOCAL_CPU filter on each boot time enabled
> CPUs.
> b) with SCOPE_SYSTEM filter only once after all boot time
> enabled CPUs are active.
>
> Cc: Dave Martin <dave.martin@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
> arch/arm64/kernel/cpufeature.c | 33 ++++++++++++++++++++++++---------
> 1 file changed, 24 insertions(+), 9 deletions(-)
>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 61d4c3cfb1cc..e1a56fa889a5 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -505,6 +505,7 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, u64 new)
>
> extern const struct arm64_cpu_capabilities arm64_errata[];
> static void update_cpu_errata_workarounds(void);
> +static void update_cpu_local_features(void);
>
> void __init init_cpu_features(struct cpuinfo_arm64 *info)
> {
> @@ -554,6 +555,7 @@ void __init init_cpu_features(struct cpuinfo_arm64 *info)
> * initialised the cpu feature infrastructure.
> */
> update_cpu_errata_workarounds();
> + update_cpu_local_features();
> }
>
> static void update_cpu_ftr_reg(struct arm64_ftr_reg *reg, u64 new)
> @@ -1387,13 +1389,15 @@ static void verify_local_cpu_errata_workarounds(void)
> static void update_cpu_errata_workarounds(void)
> {
> update_cpu_capabilities(arm64_errata,
> - ARM64_CPUCAP_SCOPE_ALL,
> + ARM64_CPUCAP_SCOPE_LOCAL_CPU,

In isolation, this looks strange because it seems to handle only a
subset of arm64_errata now.

I think I understand the change as follows:

* all previously-existing errata workarounds SCOPE_LOCAL_CPU
anyway, so the behavior here doesn't change for any existing
caps;

* the non SCOPE_SYSTEM workarounds (which this patch prepares for)
are handled by the new setup_errata_workaround() path.

Similarly, the features handling is split into two: one mirroring
the current behaviour (for SCOPE_SYSTEM this time) and one handling
the rest, for supporting SCOPE_CPU_LOCAL features in subsequent
patches.

Does that sound right?

I'm not sure we need extra comments or documentation; I just want
to check that I've understood the patch correctly.

Cheers
---Dave
> "enabling workaround for");
> }
>
> -static void __init enable_errata_workarounds(void)
> +static void update_cpu_local_features(void)
> {
> - enable_cpu_capabilities(arm64_errata, ARM64_CPUCAP_SCOPE_ALL);
> + update_cpu_capabilities(arm64_features,
> + ARM64_CPUCAP_SCOPE_LOCAL_CPU,
> + "detected feature:");
> }
>
> /*
> @@ -1430,23 +1434,34 @@ void check_local_cpu_capabilities(void)
>
> /*
> * If we haven't finalised the system capabilities, this CPU gets
> - * a chance to update the errata work arounds.
> + * a chance to update the errata work arounds and local CPU features.
> * Otherwise, this CPU should verify that it has all the system
> * advertised capabilities.
> */
> - if (!sys_caps_initialised)
> + if (!sys_caps_initialised) {
> update_cpu_errata_workarounds();
> - else
> + update_cpu_local_features();
> + } else {
> verify_local_cpu_capabilities();
> + }
> }
>
> static void __init setup_feature_capabilities(void)
> {
> update_cpu_capabilities(arm64_features,
> - ARM64_CPUCAP_SCOPE_ALL, "detected feature:");
> + ARM64_CPUCAP_SCOPE_SYSTEM,
> + "detected feature:");
> enable_cpu_capabilities(arm64_features, ARM64_CPUCAP_SCOPE_ALL);
> }
>
> +static void __init setup_errata_workarounds(void)
> +{
> + update_cpu_capabilities(arm64_errata,
> + ARM64_CPUCAP_SCOPE_SYSTEM,
> + "enabling workaround for");
> + enable_cpu_capabilities(arm64_errata, ARM64_CPUCAP_SCOPE_ALL);
> +}
> +
> DEFINE_STATIC_KEY_FALSE(arm64_const_caps_ready);
> EXPORT_SYMBOL(arm64_const_caps_ready);
>
> @@ -1468,9 +1483,9 @@ void __init setup_cpu_features(void)
> u32 cwg;
> int cls;
>
> - /* Set the CPU feature capabilies */
> + /* Finalise the CPU capabilities */
> setup_feature_capabilities();
> - enable_errata_workarounds();
> + setup_errata_workarounds();
> mark_const_caps_ready();
> setup_elf_hwcaps(arm64_elf_hwcaps);
>
> --
> 2.14.3
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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