Subject: [PATCH v7 01/20] arm64: cpufeature: Add cpucap for HPMN0

From: Colton Lewis <[email-masked]>
Date: Mon, 4 May 2026 21:17:54 +0000

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 <[email-masked]>
Reviewed-by: Suzuki K Poulose <[email-masked]>
Signed-off-by: Colton Lewis <[email-masked]>
---
 arch/arm64/kernel/cpufeature.c | 8 ++++++++
 arch/arm64/kvm/sys_regs.c      | 3 ++-
 arch/arm64/tools/cpucaps       | 1 +
 arch/arm64/tools/sysreg        | 6 +++---
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 32c2dbcc0c641..5c6c76a9696cc 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -556,6 +556,7 @@ static const struct arm64_ftr_bits ftr_id_mmfr0[] = {
 };
 
 static const struct arm64_ftr_bits ftr_id_aa64dfr0[] = {
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, 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),
@@ -2964,6 +2965,13 @@ 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/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 1b4cacb6e918a..0a8e8ee69cd00 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -3232,7 +3232,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 		    ID_AA64DFR0_EL1_DoubleLock_MASK |
 		    ID_AA64DFR0_EL1_WRPs_MASK |
 		    ID_AA64DFR0_EL1_PMUVer_MASK |
-		    ID_AA64DFR0_EL1_DebugVer_MASK),
+		    ID_AA64DFR0_EL1_DebugVer_MASK |
+		    ID_AA64DFR0_EL1_HPMN0_MASK),
 	ID_SANITISED(ID_AA64DFR1_EL1),
 	ID_UNALLOCATED(5,2),
 	ID_UNALLOCATED(5,3),
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 7261553b644b2..654b165781854 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -42,6 +42,7 @@ HAS_GIC_PRIO_MASKING
 HAS_GIC_PRIO_RELAXED_SYNC
 HAS_ICH_HCR_EL2_TDIR
 HAS_HCR_NV1
+HAS_HPMN0
 HAS_HCX
 HAS_LDAPR
 HAS_LPA2
diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg
index 9d1c211080571..92135f8834be0 100644
--- a/arch/arm64/tools/sysreg
+++ b/arch/arm64/tools/sysreg
@@ -1666,9 +1666,9 @@ 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
-- 
2.54.0.545.g6539524ca2-goog