[PATCH v6 1/1] target/arm/kvm: add kvm-psci-version vcpu property

[Sebastian Ott <sebott@redhat.com>]

Provide a kvm specific vcpu property to override the default
(as of kernel v6.13 that would be PSCI v1.3) PSCI version emulated
by kvm. Current valid values are: 0.1, 0.2, 1.0, 1.1, 1.2, and 1.3

Note: in order to support PSCI v0.1 we need to drop vcpu
initialization with KVM_CAP_ARM_PSCI_0_2 in that case.

Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Sebastian Ott <sebott@redhat.com>
---
 docs/system/arm/cpu-features.rst | 11 ++++++++
 target/arm/cpu.c                 |  8 +++++-
 target/arm/kvm.c                 | 48 ++++++++++++++++++++++++++++++--
 3 files changed, 64 insertions(+), 3 deletions(-)

diff --git a/docs/system/arm/cpu-features.rst b/docs/system/arm/cpu-features.rst
index 3db1f19401..ce19ae6a04 100644
--- a/docs/system/arm/cpu-features.rst
+++ b/docs/system/arm/cpu-features.rst
@@ -204,6 +204,17 @@ the list of KVM VCPU features and their descriptions.
   the guest scheduler behavior and/or be exposed to the guest
   userspace.
 
+``kvm-psci-version``
+  Set the Power State Coordination Interface (PSCI) firmware ABI version
+  that KVM provides to the guest. By default KVM will use the newest
+  version that it knows about (which is PSCI v1.3 in Linux v6.13).
+
+  You only need to set this if you want to be able to migrate this
+  VM to a host machine running an older kernel that does not
+  recognize the PSCI version that this host's kernel defaults to.
+
+  Current valid values are: 0.1, 0.2, 1.0, 1.1, 1.2, and 1.3.
+
 TCG VCPU Features
 =================
 
diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index 10f8280eef..60f391651d 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -1144,7 +1144,13 @@ static void arm_cpu_initfn(Object *obj)
      * picky DTB consumer will also provide a helpful error message.
      */
     cpu->dtb_compatible = "qemu,unknown";
-    cpu->psci_version = QEMU_PSCI_VERSION_0_1; /* By default assume PSCI v0.1 */
+    if (!kvm_enabled()) {
+        /* By default KVM will use the newest PSCI version that it knows about.
+         * This can be changed using the kvm-psci-version property.
+         * For others assume PSCI v0.1 by default.
+         */
+        cpu->psci_version = QEMU_PSCI_VERSION_0_1;
+    }
     cpu->kvm_target = QEMU_KVM_ARM_TARGET_NONE;
 
     if (tcg_enabled() || hvf_enabled()) {
diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index ded582e0da..5453460965 100644
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -485,6 +485,28 @@ static void kvm_steal_time_set(Object *obj, bool value, Error **errp)
     ARM_CPU(obj)->kvm_steal_time = value ? ON_OFF_AUTO_ON : ON_OFF_AUTO_OFF;
 }
 
+static char *kvm_get_psci_version(Object *obj, Error **errp)
+{
+    ARMCPU *cpu = ARM_CPU(obj);
+
+    return g_strdup_printf("%d.%d",
+                           (int) PSCI_VERSION_MAJOR(cpu->psci_version),
+                           (int) PSCI_VERSION_MINOR(cpu->psci_version));
+}
+
+static void kvm_set_psci_version(Object *obj, const char *value, Error **errp)
+{
+    ARMCPU *cpu = ARM_CPU(obj);
+    uint16_t maj, min;
+
+    if (sscanf(value, "%hd.%hd", &maj, &min) != 2) {
+        error_setg(errp, "Invalid PSCI version.");
+        return;
+    }
+
+    cpu->psci_version = PSCI_VERSION(maj, min);
+}
+
 /* KVM VCPU properties should be prefixed with "kvm-". */
 void kvm_arm_add_vcpu_properties(ARMCPU *cpu)
 {
@@ -506,6 +528,12 @@ void kvm_arm_add_vcpu_properties(ARMCPU *cpu)
                              kvm_steal_time_set);
     object_property_set_description(obj, "kvm-steal-time",
                                     "Set off to disable KVM steal time.");
+
+    object_property_add_str(obj, "kvm-psci-version", kvm_get_psci_version,
+                            kvm_set_psci_version);
+    object_property_set_description(obj, "kvm-psci-version",
+                                    "Set PSCI version. "
+                                    "Valid values are 0.1, 0.2, 1.0, 1.1, 1.2, 1.3");
 }
 
 bool kvm_arm_pmu_supported(void)
@@ -1976,8 +2004,12 @@ int kvm_arch_init_vcpu(CPUState *cs)
     if (cs->start_powered_off) {
         cpu->kvm_init_features[0] |= 1 << KVM_ARM_VCPU_POWER_OFF;
     }
-    if (kvm_check_extension(cs->kvm_state, KVM_CAP_ARM_PSCI_0_2)) {
-        cpu->psci_version = QEMU_PSCI_VERSION_0_2;
+    if (cpu->psci_version != QEMU_PSCI_VERSION_0_1 &&
+        kvm_check_extension(cs->kvm_state, KVM_CAP_ARM_PSCI_0_2)) {
+        /*
+         * Versions >= v0.2 are backward compatible with v0.2
+         * omit the feature flag for v0.1 .
+         */
         cpu->kvm_init_features[0] |= 1 << KVM_ARM_VCPU_PSCI_0_2;
     }
     if (!arm_feature(env, ARM_FEATURE_AARCH64)) {
@@ -2015,6 +2047,18 @@ int kvm_arch_init_vcpu(CPUState *cs)
         }
     }
 
+    if (cpu->psci_version) {
+        psciver = cpu->psci_version;
+        ret = kvm_set_one_reg(cs, KVM_REG_ARM_PSCI_VERSION, &psciver);
+        if (ret) {
+            error_report("KVM in this kernel does not support PSCI version %d.%d",
+                         (int) PSCI_VERSION_MAJOR(psciver),
+                         (int) PSCI_VERSION_MINOR(psciver));
+            error_printf("Consider setting the kvm-psci-version property on the "
+                         "migration source.\n");
+            return ret;
+        }
+    }
     /*
      * KVM reports the exact PSCI version it is implementing via a
      * special sysreg. If it is present, use its contents to determine
-- 
2.52.0