[PATCH 1/2] KVM: arm64: Fix MDCR_EL2.HPMN reset value

[Marc Zyngier]

The MDCR_EL2 documentation indicates that the HPMN field has
the following behaviour:

"On a Warm reset, this field resets to the expression NUM_PMU_COUNTERS."

However, it appears we reset it to zero, which is not very useful.

Add a reset helper for MDCR_EL2, and handle the case where userspace
changes the target PMU, which may force us to change HPMN again.

Reported-by: Joey Gouly <joey.gouly at arm.com>
Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/kvm/pmu-emul.c | 13 +++++++++++++
 arch/arm64/kvm/sys_regs.c |  7 ++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 6c5950b9ceac8..5a71c3744c4d7 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -1007,6 +1007,19 @@ static void kvm_arm_set_pmu(struct kvm *kvm, struct arm_pmu *arm_pmu)
 
 	kvm->arch.arm_pmu = arm_pmu;
 	kvm->arch.pmcr_n = kvm_arm_pmu_get_max_counters(kvm);
+
+	/* Reset MDCR_EL2.HPMN behind the vcpus' back... */
+	if (test_bit(KVM_ARM_VCPU_HAS_EL2, kvm->arch.vcpu_features)) {
+		struct kvm_vcpu *vcpu;
+		unsigned long i;
+
+		kvm_for_each_vcpu(i, vcpu, kvm) {
+			u64 val = __vcpu_sys_reg(vcpu, MDCR_EL2);
+			val &= ~MDCR_EL2_HPMN;
+			val |= FIELD_PREP(MDCR_EL2_HPMN, kvm->arch.pmcr_n);
+			__vcpu_sys_reg(vcpu, MDCR_EL2) = val;
+		}
+	}
 }
 
 /**
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 82430c1e1dd02..380f22f19cb42 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -2493,6 +2493,11 @@ static bool access_mdcr(struct kvm_vcpu *vcpu,
 	return true;
 }
 
+static u64 reset_mdcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
+{
+	__vcpu_sys_reg(vcpu, r->reg) = vcpu->kvm->arch.pmcr_n;
+	return vcpu->kvm->arch.pmcr_n;
+}
 
 /*
  * Architected system registers.
@@ -3034,7 +3039,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	EL2_REG(SCTLR_EL2, access_rw, reset_val, SCTLR_EL2_RES1),
 	EL2_REG(ACTLR_EL2, access_rw, reset_val, 0),
 	EL2_REG_VNCR(HCR_EL2, reset_hcr, 0),
-	EL2_REG(MDCR_EL2, access_mdcr, reset_val, 0),
+	EL2_REG(MDCR_EL2, access_mdcr, reset_mdcr, 0),
 	EL2_REG(CPTR_EL2, access_rw, reset_val, CPTR_NVHE_EL2_RES1),
 	EL2_REG_VNCR(HSTR_EL2, reset_val, 0),
 	EL2_REG_VNCR(HFGRTR_EL2, reset_val, 0),
-- 
2.39.2