target/arm/helper: Propagate MDCR_EL2.HPMN into PMCR_EL0.N

MDCR_EL2.HPMN allows an hypervisor to limit the number of PMU counters
available to EL1 and EL0 (to keep the others to itself). QEMU already
implements this split correctly, except for PMCR_EL0.N reads: the number
of counters read by EL1 or EL0 should be the one configured in
MDCR_EL2.HPMN.

Cc: qemu-stable@nongnu.org
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Message-id: 20231215144652.4193815-2-jean-philippe@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/helper.c

@@ -1475,6 +1475,22 @@ static void pmcr_write(CPUARMState *env, const ARMCPRegInfo *ri,
     pmu_op_finish(env);
 }
 
+static uint64_t pmcr_read(CPUARMState *env, const ARMCPRegInfo *ri)
+{
+    uint64_t pmcr = env->cp15.c9_pmcr;
+
+    /*
+     * If EL2 is implemented and enabled for the current security state, reads
+     * of PMCR.N from EL1 or EL0 return the value of MDCR_EL2.HPMN or HDCR.HPMN.
+     */
+    if (arm_current_el(env) <= 1 && arm_is_el2_enabled(env)) {
+        pmcr &= ~PMCRN_MASK;
+        pmcr |= (env->cp15.mdcr_el2 & MDCR_HPMN) << PMCRN_SHIFT;
+    }
+
+    return pmcr;
+}
+
 static void pmswinc_write(CPUARMState *env, const ARMCPRegInfo *ri,
                           uint64_t value)
 {
@@ -7158,8 +7174,9 @@ static void define_pmu_regs(ARMCPU *cpu)
         .fgt = FGT_PMCR_EL0,
         .type = ARM_CP_IO | ARM_CP_ALIAS,
         .fieldoffset = offsetoflow32(CPUARMState, cp15.c9_pmcr),
-        .accessfn = pmreg_access, .writefn = pmcr_write,
-        .raw_writefn = raw_write,
+        .accessfn = pmreg_access,
+        .readfn = pmcr_read, .raw_readfn = raw_read,
+        .writefn = pmcr_write, .raw_writefn = raw_write,
     };
     ARMCPRegInfo pmcr64 = {
         .name = "PMCR_EL0", .state = ARM_CP_STATE_AA64,
@@ -7169,6 +7186,7 @@ static void define_pmu_regs(ARMCPU *cpu)
         .type = ARM_CP_IO,
         .fieldoffset = offsetof(CPUARMState, cp15.c9_pmcr),
         .resetvalue = cpu->isar.reset_pmcr_el0,
+        .readfn = pmcr_read, .raw_readfn = raw_read,
         .writefn = pmcr_write, .raw_writefn = raw_write,
     };