[PATCH 6/9] KVM: arm64: PMU: Move the ID_AA64DFR0_EL1.PMUver limit to VM creation

[Marc Zyngier <maz@kernel.org>]

As further patches will enable the selection of a PMU revision
from userspace, sample the supported PMU revision at VM creation
time, rather than building each time the ID_AA64DFR0_EL1 register
is accessed.

This shouldn't result in any change in behaviour.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/include/asm/kvm_host.h |  1 +
 arch/arm64/kvm/arm.c              |  6 ++++++
 arch/arm64/kvm/pmu-emul.c         | 11 +++++++++++
 arch/arm64/kvm/sys_regs.c         | 26 +++++++++++++++++++++-----
 include/kvm/arm_pmu.h             |  6 ++++++
 5 files changed, 45 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index f38ef299f13b..411114510634 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -163,6 +163,7 @@ struct kvm_arch {
 
 	u8 pfr0_csv2;
 	u8 pfr0_csv3;
+	u8 dfr0_pmuver;
 
 	/* Hypercall features firmware registers' descriptor */
 	struct kvm_smccc_features smccc_feat;
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 8fe73ee5fa84..e4f80f0c1e97 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -164,6 +164,12 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	set_default_spectre(kvm);
 	kvm_arm_init_hypercalls(kvm);
 
+	/*
+	 * Initialise the default PMUver before there is a chance to
+	 * create an actual PMU.
+	 */
+	kvm->arch.dfr0_pmuver = kvm_arm_pmu_get_host_pmuver();
+
 	return ret;
 out_free_stage2_pgd:
 	kvm_free_stage2_pgd(&kvm->arch.mmu);
diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index ddd79b64b38a..33a88ca7b7fd 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -1021,3 +1021,14 @@ int kvm_arm_pmu_v3_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 
 	return -ENXIO;
 }
+
+u8 kvm_arm_pmu_get_host_pmuver(void)
+{
+	u64 tmp;
+
+	tmp = read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1);
+	tmp = cpuid_feature_cap_perfmon_field(tmp,
+					      ID_AA64DFR0_PMUVER_SHIFT,
+					      ID_AA64DFR0_PMUVER_8_4);
+	return FIELD_GET(ARM64_FEATURE_MASK(ID_AA64DFR0_PMUVER), tmp);
+}
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 333efddb1e27..55451f49017c 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1062,6 +1062,22 @@ static bool access_arch_timer(struct kvm_vcpu *vcpu,
 	return true;
 }
 
+static u8 pmuver_to_perfmon(const struct kvm_vcpu *vcpu)
+{
+	if (!kvm_vcpu_has_pmu(vcpu))
+		return 0;
+
+	switch (vcpu->kvm->arch.dfr0_pmuver) {
+	case ID_AA64DFR0_PMUVER_8_0:
+		return ID_DFR0_PERFMON_8_0;
+	case ID_AA64DFR0_PMUVER_IMP_DEF:
+		return 0;
+	default:
+		/* Anything ARMv8.4+ has the same value. For now. */
+		return vcpu->kvm->arch.dfr0_pmuver;
+	}
+}
+
 /* Read a sanitised cpufeature ID register by sys_reg_desc */
 static u64 read_id_reg(const struct kvm_vcpu *vcpu,
 		struct sys_reg_desc const *r, bool raz)
@@ -1112,10 +1128,10 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
 		/* Limit debug to ARMv8.0 */
 		val &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_DEBUGVER);
 		val |= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64DFR0_DEBUGVER), 6);
-		/* Limit guests to PMUv3 for ARMv8.4 */
-		val = cpuid_feature_cap_perfmon_field(val,
-						      ID_AA64DFR0_PMUVER_SHIFT,
-						      kvm_vcpu_has_pmu(vcpu) ? ID_AA64DFR0_PMUVER_8_4 : 0);
+		/* Set PMUver to the required version */
+		val &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_PMUVER);
+		val |= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64DFR0_PMUVER),
+				  kvm_vcpu_has_pmu(vcpu) ? vcpu->kvm->arch.dfr0_pmuver : 0);
 		/* Hide SPE from guests */
 		val &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_PMSVER);
 		break;
@@ -1123,7 +1139,7 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
 		/* Limit guests to PMUv3 for ARMv8.4 */
 		val = cpuid_feature_cap_perfmon_field(val,
 						      ID_DFR0_PERFMON_SHIFT,
-						      kvm_vcpu_has_pmu(vcpu) ? ID_DFR0_PERFMON_8_4 : 0);
+						      pmuver_to_perfmon(vcpu));
 		break;
 	}
 
diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
index 96b192139a23..6bda9b071084 100644
--- a/include/kvm/arm_pmu.h
+++ b/include/kvm/arm_pmu.h
@@ -89,6 +89,8 @@ void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu);
 			vcpu->arch.pmu.events = *kvm_get_pmu_events();	\
 	} while (0)
 
+u8 kvm_arm_pmu_get_host_pmuver(void);
+
 #else
 struct kvm_pmu {
 };
@@ -154,6 +156,10 @@ static inline u64 kvm_pmu_get_pmceid(struct kvm_vcpu *vcpu, bool pmceid1)
 static inline void kvm_pmu_update_vcpu_events(struct kvm_vcpu *vcpu) {}
 static inline void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu) {}
 static inline void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu) {}
+static inline u8 kvm_arm_pmu_get_host_pmuver(void)
+{
+	return 0;
+}
 
 #endif
 
-- 
2.34.1