KVM: arm64: nv: Reload PMU events upon MDCR_EL2.HPME change

MDCR_EL2.HPME is the 'global' enable bit for event counters reserved for
EL2. Give the PMU a kick when it's changed to ensure events are
reprogrammed before returning to the guest.

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241217175550.3658212-1-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/kvm/sys_regs.c

@@ -2448,6 +2448,26 @@ static unsigned int s1pie_el2_visibility(const struct kvm_vcpu *vcpu,
 	return __el2_visibility(vcpu, rd, s1pie_visibility);
 }
 
+static bool access_mdcr(struct kvm_vcpu *vcpu,
+			struct sys_reg_params *p,
+			const struct sys_reg_desc *r)
+{
+	u64 old = __vcpu_sys_reg(vcpu, MDCR_EL2);
+
+	if (!access_rw(vcpu, p, r))
+		return false;
+
+	/*
+	 * Request a reload of the PMU to enable/disable the counters affected
+	 * by HPME.
+	 */
+	if ((old ^ __vcpu_sys_reg(vcpu, MDCR_EL2)) & MDCR_EL2_HPME)
+		kvm_make_request(KVM_REQ_RELOAD_PMU, vcpu);
+
+	return true;
+}
+
+
 /*
  * Architected system registers.
  * Important: Must be sorted ascending by Op0, Op1, CRn, CRm, Op2
@@ -2981,7 +3001,7 @@ 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_rw, reset_val, 0),
+	EL2_REG(MDCR_EL2, access_mdcr, reset_val, 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),