[PATCH RFC 07/22] arm/cpuhp: Init PMU at host for all possible vcpus

[Salil Mehta]

PMU for all possible vcpus must be initialized at the virt machine
initialization time. This patch refactors existing code to accomodate possible
vcpus. This also assumes that all processor being used are identical at least
for now but does not affect the normal scanarios where they might not be in
future. This assumption only affects the future hotplug scenarios if ever there
exists any hetergenous processors. In such a case PMU might not be enabled on
some vcpus. Is it acceptable and doable tradeoff for now?

This perhaps needs more discussion. please check below link,
Link: https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg00131.html

Co-developed-by: Keqian Zhu <zhukeqian1@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
---
 hw/arm/virt.c         | 51 ++++++++++++++++++++++++++++++-------------
 include/hw/arm/virt.h |  1 +
 2 files changed, 37 insertions(+), 15 deletions(-)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 9e55b20685..7f938f289b 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -525,23 +525,9 @@ static void fdt_add_gic_node(VirtMachineState *vms)
 
 static void fdt_add_pmu_nodes(const VirtMachineState *vms)
 {
-    CPUState *cpu;
     ARMCPU *armcpu;
     uint32_t irqflags = GIC_FDT_IRQ_FLAGS_LEVEL_HI;
 
-    CPU_FOREACH(cpu) {
-        armcpu = ARM_CPU(cpu);
-        if (!arm_feature(&armcpu->env, ARM_FEATURE_PMU)) {
-            return;
-        }
-        if (kvm_enabled()) {
-            if (kvm_irqchip_in_kernel()) {
-                kvm_arm_pmu_set_irq(cpu, PPI(VIRTUAL_PMU_IRQ));
-            }
-            kvm_arm_pmu_init(cpu);
-        }
-    }
-
     if (vms->gic_version == VIRT_GIC_VERSION_2) {
         irqflags = deposit32(irqflags, GIC_FDT_IRQ_PPI_CPU_START,
                              GIC_FDT_IRQ_PPI_CPU_WIDTH,
@@ -1414,6 +1400,38 @@ static void create_secure_ram(VirtMachineState *vms,
     g_free(nodename);
 }
 
+static bool virt_pmu_init(VirtMachineState *vms)
+{
+    CPUArchIdList *possible_cpus = vms->parent.possible_cpus;
+    ARMCPU *armcpu;
+    int n;
+
+    /*
+     * As of now KVM ensures that within the host all the vcpus have same
+     * features configured. This cannot be changed later and cannot be diferent
+     * for new vcpus being plugged in. Also, -cpu option/virt machine cpu-type
+     * ensures all the vcpus are identical.
+     */
+    for (n = 0; n < possible_cpus->len; n++) {
+        CPUState *cpu = qemu_get_possible_cpu(n);
+        armcpu = ARM_CPU(cpu);
+
+        if (!arm_feature(&armcpu->env, ARM_FEATURE_PMU)) {
+            warn_report("Not all vcpus might have PMU initialized");
+            return false;
+        }
+
+        if (kvm_enabled()) {
+            if (kvm_irqchip_in_kernel()) {
+                kvm_arm_pmu_set_irq(cpu, PPI(VIRTUAL_PMU_IRQ));
+            }
+            kvm_arm_pmu_init(cpu);
+        }
+    }
+
+    return true;
+}
+
 static void *machvirt_dtb(const struct arm_boot_info *binfo, int *fdt_size)
 {
     const VirtMachineState *board = container_of(binfo, VirtMachineState,
@@ -1909,7 +1927,10 @@ static void machvirt_init(MachineState *machine)
 
     create_gic(vms);
 
-    fdt_add_pmu_nodes(vms);
+    if (!vmc->no_pmu && virt_pmu_init(vms)) {
+        vms->pmu = true;
+        fdt_add_pmu_nodes(vms);
+    }
 
     create_uart(vms, VIRT_UART, sysmem, serial_hd(0));
 
diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
index 38a9cad168..3ffbda6217 100644
--- a/include/hw/arm/virt.h
+++ b/include/hw/arm/virt.h
@@ -134,6 +134,7 @@ typedef struct {
     bool its;
     bool virt;
     bool ras;
+    bool pmu;
     OnOffAuto acpi;
     VirtGICType gic_version;
     VirtIOMMUType iommu;
-- 
2.17.1