target/arm: GICv5 cpuif: Implement ICC_HPPIR_EL1

Implement ICC_HPPIR_EL1, which the guest can use to read the current
highest priority pending interrupt.  Like APR, PCR and CR0, this is
banked, with the _EL1 register reading the answer for the current
logical interrupt domain, and the _EL3 register reading the answer
for the EL3 interrupt domain.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Message-id: 20260327111700.795099-47-peter.maydell@linaro.org

hw/intc/arm_gicv5.c

@@ -527,6 +527,16 @@ static void irs_recall_hppis(GICv5 *s, GICv5Domain domain)
     }
 }
 
+GICv5PendingIrq gicv5_get_hppi(GICv5Common *cs, GICv5Domain domain,
+                               uint32_t iaffid)
+{
+    GICv5 *s = ARM_GICV5(cs);
+    int cpuidx = irs_cpuidx_from_iaffid(cs, iaffid);
+
+    assert(cpuidx >= 0);
+    return s->hppi[domain][cpuidx];
+}
+
 static hwaddr l1_iste_addr(GICv5Common *cs, const GICv5ISTConfig *cfg,
                            uint32_t id)
 {

include/hw/intc/arm_gicv5_stream.h

@@ -175,4 +175,17 @@ uint64_t gicv5_request_config(GICv5Common *cs, uint32_t id, GICv5Domain domain,
  */
 void gicv5_forward_interrupt(ARMCPU *cpu, GICv5Domain domain);
 
+/**
+ * gicv5_get_hppi
+ * @cs: GIC IRS to query
+ * @domain: interrupt domain to act on
+ * @iaffid: IAFFID of this CPU interface
+ *
+ * Ask the IRS for the highest priority pending interrupt that it has
+ * for this CPU. This returns the equivalent of what in the stream
+ * protocol is the outstanding interrupt sent with a Forward packet.
+ */
+GICv5PendingIrq gicv5_get_hppi(GICv5Common *cs, GICv5Domain domain,
+                               uint32_t iaffid);
+
 #endif

target/arm/tcg/gicv5-cpuif.c

@@ -51,6 +51,10 @@ FIELD(ICC_CR0, PID, 38, 1)
 
 FIELD(ICC_PCR, PRIORITY, 0, 5)
 
+FIELD(ICC_HPPIR_EL1, ID, 0, 24)
+FIELD(ICC_HPPIR_EL1, TYPE, 29, 3)
+FIELD(ICC_HPPIR_EL1, HPPIV, 32, 1)
+
 /*
  * We implement 24 bits of interrupt ID, the mandated 5 bits of priority,
  * and no legacy GICv3.3 vcpu interface (yet)
@@ -114,6 +118,51 @@ static uint64_t gic_running_prio(CPUARMState *env, GICv5Domain domain)
     return hap < 32 ? hap : PRIO_IDLE;
 }
 
+static GICv5PendingIrq gic_hppi(CPUARMState *env, GICv5Domain domain)
+{
+    /*
+     * Return the current highest priority pending interrupt for the
+     * specified domain, if it has sufficient priority to preempt. The
+     * intid field of the return value will be in the format of the
+     * ICC_HPPIR register (and will be zero if and only if there is no
+     * interrupt that can preempt).
+     */
+
+    GICv5Common *gic = gicv5_get_gic(env);
+    GICv5PendingIrq best, irs_hppi;
+
+    if (!(env->gicv5_cpuif.icc_cr0[domain] & R_ICC_CR0_EN_MASK)) {
+        /* If cpuif is disabled there is no HPPI */
+        return (GICv5PendingIrq) { .intid = 0, .prio = PRIO_IDLE };
+    }
+
+    irs_hppi = gicv5_get_hppi(gic, domain, env->gicv5_iaffid);
+
+    /*
+     * If the best PPI and the best interrupt from the IRS have the
+     * same priority, it's IMPDEF which we pick (R_VVBPS). We choose
+     * the PPI.
+     */
+    if (env->gicv5_cpuif.ppi_hppi[domain].prio <= irs_hppi.prio) {
+        best = env->gicv5_cpuif.ppi_hppi[domain];
+    } else {
+        best = irs_hppi;
+    }
+
+    /*
+     * D_MSQKF: an interrupt has sufficient priority if its priority
+     * is higher than the current running priority and equal to or
+     * higher than the priority mask.
+     */
+    if (best.prio == PRIO_IDLE ||
+        best.prio > env->gicv5_cpuif.icc_pcr[domain] ||
+        best.prio >= gic_running_prio(env, domain)) {
+        return (GICv5PendingIrq) { .intid = 0, .prio = PRIO_IDLE };
+    }
+    best.intid |= R_ICC_HPPIR_EL1_HPPIV_MASK;
+    return best;
+}
+
 static void gic_recalc_ppi_hppi(CPUARMState *env)
 {
     /*
@@ -407,6 +456,13 @@ static void gic_icc_pcr_el1_reset(CPUARMState *env, const ARMCPRegInfo *ri)
     }
 }
 
+static uint64_t gic_icc_hppir_el1_read(CPUARMState *env, const ARMCPRegInfo *ri)
+{
+    GICv5Domain domain = gicv5_logical_domain(env);
+    GICv5PendingIrq hppi = gic_hppi(env, domain);
+    return hppi.intid;
+}
+
 static const ARMCPRegInfo gicv5_cpuif_reginfo[] = {
     /*
      * Barrier: wait until the effects of a cpuif system register
@@ -522,6 +578,11 @@ static const ARMCPRegInfo gicv5_cpuif_reginfo[] = {
         .fieldoffset = offsetof(CPUARMState, gicv5_cpuif.ppi_hm[1]),
         .resetvalue = PPI_HMR1_RESET,
     },
+    {   .name = "ICC_HPPIR_EL1", .state = ARM_CP_STATE_AA64,
+        .opc0 = 3, .opc1 = 0, .crn = 12, .crm = 10, .opc2 = 3,
+        .access = PL1_R, .type = ARM_CP_IO | ARM_CP_NO_RAW,
+        .readfn = gic_icc_hppir_el1_read,
+    },
     {   .name = "ICC_PPI_ENABLER0_EL1", .state = ARM_CP_STATE_AA64,
         .opc0 = 3, .opc1 = 0, .crn = 12, .crm = 10, .opc2 = 6,
         .access = PL1_RW, .type = ARM_CP_IO | ARM_CP_NO_RAW,