KVM: arm64: Move PMUVer filtering into KVM code

The supported guest PMU version on a particular platform is ultimately a
KVM decision. Move PMUVer filtering into KVM code.

Tested-by: Janne Grunau <j@jannau.net>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250305202641.428114-9-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Author: oupton

arch/arm64/include/asm/cpufeature.h

@@ -525,29 +525,6 @@ cpuid_feature_extract_unsigned_field(u64 features, int field)
 	return cpuid_feature_extract_unsigned_field_width(features, field, 4);
 }
 
-/*
- * Fields that identify the version of the Performance Monitors Extension do
- * not follow the standard ID scheme. See ARM DDI 0487E.a page D13-2825,
- * "Alternative ID scheme used for the Performance Monitors Extension version".
- */
-static inline u64 __attribute_const__
-cpuid_feature_cap_perfmon_field(u64 features, int field, u64 cap)
-{
-	u64 val = cpuid_feature_extract_unsigned_field(features, field);
-	u64 mask = GENMASK_ULL(field + 3, field);
-
-	/* Treat IMPLEMENTATION DEFINED functionality as unimplemented */
-	if (val == ID_AA64DFR0_EL1_PMUVer_IMP_DEF)
-		val = 0;
-
-	if (val > cap) {
-		features &= ~mask;
-		features |= (cap << field) & mask;
-	}
-
-	return features;
-}
-
 static inline u64 arm64_ftr_mask(const struct arm64_ftr_bits *ftrp)
 {
 	return (u64)GENMASK(ftrp->shift + ftrp->width - 1, ftrp->shift);

arch/arm64/kvm/pmu-emul.c

@@ -1226,13 +1226,16 @@ int kvm_arm_pmu_v3_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 
 u8 kvm_arm_pmu_get_pmuver_limit(void)
 {
-	u64 tmp;
+	unsigned int pmuver;
 
-	tmp = read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1);
-	tmp = cpuid_feature_cap_perfmon_field(tmp,
-					      ID_AA64DFR0_EL1_PMUVer_SHIFT,
-					      ID_AA64DFR0_EL1_PMUVer_V3P5);
-	return FIELD_GET(ARM64_FEATURE_MASK(ID_AA64DFR0_EL1_PMUVer), tmp);
+	pmuver = SYS_FIELD_GET(ID_AA64DFR0_EL1, PMUVer,
+			       read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1));
+
+	/* Treat IMPLEMENTATION DEFINED functionality as unimplemented */
+	if (pmuver == ID_AA64DFR0_EL1_PMUVer_IMP_DEF)
+		return 0;
+
+	return min(pmuver, ID_AA64DFR0_EL1_PMUVer_V3P5);
 }
 
 /**