Re: [PATCH v6 16/21] arm64: cpufeature: Enumerate support for Enhanced Counter Virtualization

[Marc Zyngier <maz@kernel.org>]

On Wed, 04 Aug 2021 09:58:14 +0100,
Oliver Upton <oupton@google.com> wrote:
> 
> Introduce a new cpucap to indicate if the system supports full enhanced
> counter virtualization (i.e. ID_AA64MMFR0_EL1.ECV==0x2).
> 
> Signed-off-by: Oliver Upton <oupton@google.com>
> ---
>  arch/arm64/include/asm/sysreg.h |  2 ++
>  arch/arm64/kernel/cpufeature.c  | 10 ++++++++++
>  arch/arm64/tools/cpucaps        |  1 +
>  3 files changed, 13 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index 7b9c3acba684..4dfc44066dfb 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -847,6 +847,8 @@
>  #define ID_AA64MMFR0_ASID_SHIFT		4
>  #define ID_AA64MMFR0_PARANGE_SHIFT	0
>  
> +#define ID_AA64MMFR0_ECV_VIRT		0x1
> +#define ID_AA64MMFR0_ECV_PHYS		0x2
>  #define ID_AA64MMFR0_TGRAN4_NI		0xf
>  #define ID_AA64MMFR0_TGRAN4_SUPPORTED	0x0
>  #define ID_AA64MMFR0_TGRAN64_NI		0xf
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 0ead8bfedf20..94c349e179d3 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -2301,6 +2301,16 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>  		.matches = has_cpuid_feature,
>  		.min_field_value = 1,
>  	},
> +	{
> +		.desc = "Enhanced Counter Virtualization (Physical)",
> +		.capability = ARM64_ECV,
> +		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
> +		.sys_reg = SYS_ID_AA64MMFR0_EL1,
> +		.sign = FTR_UNSIGNED,
> +		.field_pos = ID_AA64MMFR0_ECV_SHIFT,
> +		.matches = has_cpuid_feature,
> +		.min_field_value = ID_AA64MMFR0_ECV_PHYS,
> +	},
>  	{},
>  };
>  
> diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
> index 49305c2e6dfd..d819ea614da5 100644
> --- a/arch/arm64/tools/cpucaps
> +++ b/arch/arm64/tools/cpucaps
> @@ -3,6 +3,7 @@
>  # Internal CPU capabilities constants, keep this list sorted
>  
>  BTI
> +ECV
>  # Unreliable: use system_supports_32bit_el0() instead.
>  HAS_32BIT_EL0_DO_NOT_USE
>  HAS_32BIT_EL1

As discussed in another context, we probably want both ECV and ECV2 to
distinguish the two feature sets that ECV has so far.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.