linux-kernel - Re: [PATCH v4 01/23] arm64: cpufeature: Add cpucap for HPMN0

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Message-ID: <153b5191-c585-433e-9cf5-1ed19b9a7f5c@arm.com>
Date: Wed, 16 Jul 2025 00:22:16 +0100
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Colton Lewis <coltonlewis@...gle.com>, kvm@...r.kernel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>,
 Russell King <linux@...linux.org.uk>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
 Mingwei Zhang <mizhang@...gle.com>, Joey Gouly <joey.gouly@....com>,
 Zenghui Yu <yuzenghui@...wei.com>, Mark Rutland <mark.rutland@....com>,
 Shuah Khan <shuah@...nel.org>, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 kvmarm@...ts.linux.dev, linux-perf-users@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 01/23] arm64: cpufeature: Add cpucap for HPMN0

On 14/07/2025 23:58, Colton Lewis wrote:
> Add a capability for FEAT_HPMN0, whether MDCR_EL2.HPMN can specify 0
> counters reserved for the guest.
> 
> This required changing HPMN0 to an UnsignedEnum in tools/sysreg
> because otherwise not all the appropriate macros are generated to add
> it to arm64_cpu_capabilities_arm64_features.
> 
> Acked-by: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Colton Lewis <coltonlewis@...gle.com>
> ---
>   arch/arm64/kernel/cpufeature.c | 8 ++++++++
>   arch/arm64/tools/cpucaps       | 1 +
>   arch/arm64/tools/sysreg        | 6 +++---
>   3 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index b34044e20128..f38d7b5294ec 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -548,6 +548,7 @@ static const struct arm64_ftr_bits ftr_id_mmfr0[] = {
>   };
>   
>   static const struct arm64_ftr_bits ftr_id_aa64dfr0[] = {
> +	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64DFR0_EL1_HPMN0_SHIFT, 4, 0),

This doesn't have to be FTR_STRICT. The kernel can deal with 
differences, by skipping to use HPMN0. We anyway rely on the
system wide cap for using the feature.

Otherwise,

Acked-by: Suzuki K Poulose <suzuki.poulose@....com>


>   	S_ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64DFR0_EL1_DoubleLock_SHIFT, 4, 0),
>   	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64DFR0_EL1_PMSVer_SHIFT, 4, 0),
>   	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64DFR0_EL1_CTX_CMPs_SHIFT, 4, 0),
> @@ -2896,6 +2897,13 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>   		.matches = has_cpuid_feature,
>   		ARM64_CPUID_FIELDS(ID_AA64MMFR0_EL1, FGT, FGT2)
>   	},
> +	{
> +		.desc = "HPMN0",
> +		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
> +		.capability = ARM64_HAS_HPMN0,
> +		.matches = has_cpuid_feature,
> +		ARM64_CPUID_FIELDS(ID_AA64DFR0_EL1, HPMN0, IMP)
> +	},
>   #ifdef CONFIG_ARM64_SME
>   	{
>   		.desc = "Scalable Matrix Extension",
> diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
> index 10effd4cff6b..5b196ba21629 100644
> --- a/arch/arm64/tools/cpucaps
> +++ b/arch/arm64/tools/cpucaps
> @@ -39,6 +39,7 @@ HAS_GIC_CPUIF_SYSREGS
>   HAS_GIC_PRIO_MASKING
>   HAS_GIC_PRIO_RELAXED_SYNC
>   HAS_HCR_NV1
> +HAS_HPMN0
>   HAS_HCX
>   HAS_LDAPR
>   HAS_LPA2
> diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg
> index 8a8cf6874298..d29742481754 100644
> --- a/arch/arm64/tools/sysreg
> +++ b/arch/arm64/tools/sysreg
> @@ -1531,9 +1531,9 @@ EndEnum
>   EndSysreg
>   
>   Sysreg	ID_AA64DFR0_EL1	3	0	0	5	0
> -Enum	63:60	HPMN0
> -	0b0000	UNPREDICTABLE
> -	0b0001	DEF
> +UnsignedEnum	63:60	HPMN0
> +	0b0000	NI
> +	0b0001	IMP
>   EndEnum
>   UnsignedEnum	59:56	ExtTrcBuff
>   	0b0000	NI