linux-kernel - Re: [PATCH 07/16] arm64: capabilities: Filter the entries based on a given type

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Message-ID: <20180126112217.GO5862@e103592.cambridge.arm.com>
Date:   Fri, 26 Jan 2018 11:22:18 +0000
From:   Dave Martin <Dave.Martin@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, mark.rutland@....com,
        ckadabi@...eaurora.org, ard.biesheuvel@...aro.org,
        marc.zyngier@....com, catalin.marinas@....com, will.deacon@....com,
        linux-kernel@...r.kernel.org, jnair@...iumnetworks.com
Subject: Re: [PATCH 07/16] arm64: capabilities: Filter the entries based on a
 given type

On Tue, Jan 23, 2018 at 12:28:00PM +0000, Suzuki K Poulose wrote:
> While processing the list of capabilities, it is useful to
> filter out some of the entries based on the given type to
> allow better control. This can be used later for handling
> LOCAL vs SYSTEM wide capabilities and more.
> 
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>  arch/arm64/include/asm/cpufeature.h |  5 +++++
>  arch/arm64/kernel/cpufeature.c      | 30 ++++++++++++++++++++----------
>  2 files changed, 25 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index 27d037bb0451..a621d2184227 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -99,6 +99,11 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
>  /* Is it safe for a late CPU to miss this capability when system has it */
>  #define ARM64_CPUCAP_LATE_CPU_SAFE_TO_MISS	BIT(3)
>  
> +#define ARM64_CPUCAP_TYPE_ALL			 \
> +	(ARM64_CPUCAP_SCOPE_LOCAL_CPU		|\
> +	 ARM64_CPUCAP_SCOPE_SYSTEM		|\
> +	 ARM64_CPUCAP_LATE_CPU_SAFE_TO_HAVE	|\
> +	 ARM64_CPUCAP_LATE_CPU_SAFE_TO_MISS)

Nit: can we have another tab between | and \?

This will help to make missing |s stand out more if/when more entries
are added to this list in future.

>  /*
>   * CPU errata detected at boot time based on feature of one or more CPUs.
>   * It is not safe for a late CPU to have this feature when the system doesn't
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 79737034a628..198c5daddd65 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1180,9 +1180,11 @@ static bool __this_cpu_has_cap(const struct arm64_cpu_capabilities *cap_array,
>  }
>  
>  static void update_cpu_capabilities(const struct arm64_cpu_capabilities *caps,
> -			    const char *info)
> +				    u16 cap_type, const char *info)

Semantically "cap_type" represents a set of accepted types, not a single
type here.

Can we rename it to "cap_types", "cap_type_mask" or similar?

>  {
>  	for (; caps->matches; caps++) {
> +		if (!(caps->type & cap_type))
> +			continue;

Minor nit: insert a blank line here?

To me, lack of a blank line suggests that the code will always fall
through to the next line, which is not the case after
return/continue/break/goto.

Alternatively:

		if (!(caps->type & cap_type) ||
		    !caps->matches(caps, caps->def_scope))
			continue;

still seems fairly intelligible ...[1]

>  		if (!caps->matches(caps, cpucap_default_scope(caps)))
>  			continue;
>  
> @@ -1204,12 +1206,13 @@ static int __enable_cpu_capability(void *arg)
>   * Run through the enabled capabilities and enable() it on all active
>   * CPUs
>   */
> -static void __init enable_cpu_capabilities(const struct arm64_cpu_capabilities *caps)
> +static void __init
> +enable_cpu_capabilities(const struct arm64_cpu_capabilities *caps, u16 caps_type)

The "caps_type" argument should be named consistently with the
corresponding argument to update_cpu_capabilities().

>  {
>  	for (; caps->matches; caps++) {
>  		unsigned int num = caps->capability;
>  
> -		if (!cpus_have_cap(num))
> +		if (!(caps->type & caps_type) || !cpus_have_cap(num))

[1]... and would match the approach taken here.

>  			continue;
>  
>  		/* Ensure cpus_have_const_cap(num) works */
> @@ -1231,12 +1234,16 @@ static void __init enable_cpu_capabilities(const struct arm64_cpu_capabilities *
>   * Run through the list of capabilities to check for conflicts.
>   * Returns "false" on conflicts.
>   */
> -static bool __verify_local_cpu_caps(const struct arm64_cpu_capabilities *caps_list)
> +static bool __verify_local_cpu_caps(const struct arm64_cpu_capabilities *caps_list,
> +				    u16 caps_type)
>  {
>  	bool cpu_has_cap, system_has_cap;
>  	const struct arm64_cpu_capabilities *caps = caps_list;
>  
>  	for (; caps->matches; caps++) {
> +		if (!(caps->type & caps_type))
> +			continue;
> +
>  		cpu_has_cap = __this_cpu_has_cap(caps_list, caps->capability);
>  		system_has_cap =  cpus_have_cap(caps->capability);
>  
> @@ -1299,7 +1306,7 @@ verify_local_elf_hwcaps(const struct arm64_cpu_capabilities *caps)
>  
>  static void verify_local_cpu_features(void)
>  {
> -	if (!__verify_local_cpu_caps(arm64_features))
> +	if (!__verify_local_cpu_caps(arm64_features, ARM64_CPUCAP_TYPE_ALL))
>  		cpu_die_early();
>  }
>  
> @@ -1327,18 +1334,20 @@ static void verify_sve_features(void)
>   */
>  static void verify_local_cpu_errata_workarounds(void)
>  {
> -	if (__verify_local_cpu_caps(arm64_errata))
> +	if (!__verify_local_cpu_caps(arm64_errata, ARM64_CPUCAP_TYPE_ALL))
>  		cpu_die_early();

Did you mean to insert the ! here?

[...]

Cheers
---Dave