linux-kernel - Re: [PATCH 01/17] arm64: cpufeature: Add cpucap for HPMN0

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Message-ID: <gsnt7c1s35yj.fsf@coltonlewis-kvm.c.googlers.com>
Date: Tue, 03 Jun 2025 20:50:28 +0000
From: Colton Lewis <coltonlewis@...gle.com>
To: Oliver Upton <oliver.upton@...ux.dev>
Cc: kvm@...r.kernel.org, pbonzini@...hat.com, corbet@....net, 
	linux@...linux.org.uk, catalin.marinas@....com, will@...nel.org, 
	maz@...nel.org, joey.gouly@....com, suzuki.poulose@....com, 
	yuzenghui@...wei.com, mark.rutland@....com, 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 01/17] arm64: cpufeature: Add cpucap for HPMN0

Hi Oliver. Thanks for the speedy response.

Oliver Upton <oliver.upton@...ux.dev> writes:

> Hi Colton,

> On Mon, Jun 02, 2025 at 07:26:46PM +0000, 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.

>> 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 a3da020f1d1c..578eea321a60 100644
>> --- a/arch/arm64/kernel/cpufeature.c
>> +++ b/arch/arm64/kernel/cpufeature.c
>> @@ -541,6 +541,7 @@ 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),
>>   	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),
>> @@ -2884,6 +2885,13 @@ static const struct arm64_cpu_capabilities  
>> arm64_features[] = {
>>   		.matches = has_cpuid_feature,
>>   		ARM64_CPUID_FIELDS(ID_AA64MMFR0_EL1, FGT, FGT2)
>>   	},
>> +	{
>> +		.desc = "Hypervisor PMU Partitioning 0 Guest Counters",

> nit: just use the the FEAT_xxx name for the description (i.e. "HPMN0").

Okay