Re: [PATCH v2 07/14] KVM: arm64: Use a cpucap to determine if system supports FEAT_PMUv3

KVM is about to learn some new tricks to virtualize PMUv3 on IMPDEF
hardware. As part of that, we now need to differentiate host support
from guest support for PMUv3.

Add a cpucap to determine if an architectural PMUv3 is present to guard
host usage of PMUv3 controls.

Tested-by: Janne Grunau <j@jannau.net>
Signed-off-by: Oliver Upton <redacted>
---
 arch/arm64/include/asm/cpufeature.h     |  5 +++++
 arch/arm64/kernel/cpufeature.c          | 19 +++++++++++++++++++
 arch/arm64/kvm/hyp/include/hyp/switch.h |  4 ++--
 arch/arm64/kvm/pmu.c                    | 10 +++++-----
 arch/arm64/tools/cpucaps                |  1 +
 include/kvm/arm_pmu.h                   |  2 +-
 6 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index e0e4478f5fb5..0eff048848b8 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h

@@ -866,6 +866,11 @@ static __always_inline bool system_supports_mpam_hcr(void)
 	return alternative_has_cap_unlikely(ARM64_MPAM_HCR);
 }
 
+static inline bool system_supports_pmuv3(void)
+{
+	return cpus_have_final_cap(ARM64_HAS_PMUV3);
+}
+
 int do_emulate_mrs(struct pt_regs *regs, u32 sys_reg, u32 rt);
 bool try_emulate_mrs(struct pt_regs *regs, u32 isn);
 

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 4eb7c6698ae4..6886d2875fac 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c

@@ -1898,6 +1898,19 @@ static bool has_lpa2(const struct arm64_cpu_capabilities *entry, int scope)
 }
 #endif
 
+static bool has_pmuv3(const struct arm64_cpu_capabilities *entry, int scope)
+{
+	u64 dfr0 = read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1);
+	unsigned int pmuver;
+
+	pmuver = cpuid_feature_extract_unsigned_field(dfr0,
+						      ID_AA64DFR0_EL1_PMUVer_SHIFT);
+	if (pmuver == ID_AA64DFR0_EL1_PMUVer_IMP_DEF)
+		return false;
+
+	return pmuver >= ID_AA64DFR0_EL1_PMUVer_IMP;

+}
+
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
 #define KPTI_NG_TEMP_VA		(-(1UL << PMD_SHIFT))
 

@@ -2999,6 +3012,12 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		ARM64_CPUID_FIELDS(ID_AA64PFR1_EL1, GCS, IMP)
 	},
 #endif
+	{
+		.desc = "PMUv3",
+		.capability = ARM64_HAS_PMUV3,
+		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.matches = has_pmuv3,
+	},

 	{},
 };
 

diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index f838a45665f2..0edc7882bedb 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h

@@ -244,7 +244,7 @@ static inline void __activate_traps_common(struct kvm_vcpu *vcpu)
 	 * counter, which could make a PMXEVCNTR_EL0 access UNDEF at
 	 * EL1 instead of being trapped to EL2.
 	 */
-	if (kvm_arm_support_pmu_v3()) {
+	if (system_supports_pmuv3()) {