KVM: Allow KVM_CHECK_EXTENSION on the vm fd

The KVM_CHECK_EXTENSION is only available on the kvm fd today. Unfortunately
on PPC some of the capabilities change depending on the way a VM was created.

So instead we need a way to expose capabilities as VM ioctl, so that we can
see which VM type we're using (HV or PR). To enable this, add the
KVM_CHECK_EXTENSION ioctl to our vm ioctl portfolio.

Signed-off-by: Alexander Graf <agraf@suse.de>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>

3 files changed, 37 insertions, 29 deletions

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 884f819e1908..8898caf8c090 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -148,9 +148,9 @@ of banks, as set via the KVM_X86_SETUP_MCE ioctl.
 
 4.4 KVM_CHECK_EXTENSION
 
-Capability: basic
+Capability: basic, KVM_CAP_CHECK_EXTENSION_VM for vm ioctl
 Architectures: all
-Type: system ioctl
+Type: system ioctl, vm ioctl
 Parameters: extension identifier (KVM_CAP_*)
 Returns: 0 if unsupported; 1 (or some other positive integer) if supported
 
@@ -160,6 +160,9 @@ receives an integer that describes the extension availability.
 Generally 0 means no and 1 means yes, but some extensions may report
 additional information in the integer return value.
 
+Based on their initialization different VMs may have different capabilities.
+It is thus encouraged to use the vm ioctl to query for capabilities (available
+with KVM_CAP_CHECK_EXTENSION_VM on the vm fd)
 
 4.5 KVM_GET_VCPU_MMAP_SIZE
 
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 0418b746cb68..51776cac6a9b 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -759,6 +759,7 @@ struct kvm_ppc_smmu_info {
 #define KVM_CAP_ARM_PSCI_0_2 102
 #define KVM_CAP_PPC_FIXUP_HCALL 103
 #define KVM_CAP_PPC_ENABLE_HCALL 104
+#define KVM_CAP_CHECK_EXTENSION_VM 105
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e28f3caa539d..1b95cc926cfc 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2324,6 +2324,34 @@ static int kvm_ioctl_create_device(struct kvm *kvm,
         return 0;
 }
 
+static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
+{
+        switch (arg) {
+        case KVM_CAP_USER_MEMORY:
+        case KVM_CAP_DESTROY_MEMORY_REGION_WORKS:
+        case KVM_CAP_JOIN_MEMORY_REGIONS_WORKS:
+#ifdef CONFIG_KVM_APIC_ARCHITECTURE
+        case KVM_CAP_SET_BOOT_CPU_ID:
+#endif
+        case KVM_CAP_INTERNAL_ERROR_DATA:
+#ifdef CONFIG_HAVE_KVM_MSI
+        case KVM_CAP_SIGNAL_MSI:
+#endif
+#ifdef CONFIG_HAVE_KVM_IRQ_ROUTING
+        case KVM_CAP_IRQFD_RESAMPLE:
+#endif
+        case KVM_CAP_CHECK_EXTENSION_VM:
+                return 1;
+#ifdef CONFIG_HAVE_KVM_IRQ_ROUTING
+        case KVM_CAP_IRQ_ROUTING:
+                return KVM_MAX_IRQ_ROUTES;
+#endif
+        default:
+                break;
+        }
+        return kvm_vm_ioctl_check_extension(kvm, arg);
+}
+
 static long kvm_vm_ioctl(struct file *filp,
                            unsigned int ioctl, unsigned long arg)
 {
@@ -2487,6 +2515,9 @@ static long kvm_vm_ioctl(struct file *filp,
                 r = 0;
                 break;
         }
+        case KVM_CHECK_EXTENSION:
+                r = kvm_vm_ioctl_check_extension_generic(kvm, arg);
+                break;
         default:
                 r = kvm_arch_vm_ioctl(filp, ioctl, arg);
                 if (r == -ENOTTY)
@@ -2571,33 +2602,6 @@ static int kvm_dev_ioctl_create_vm(unsigned long type)
         return r;
 }
 
-static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
-{
-        switch (arg) {
-        case KVM_CAP_USER_MEMORY:
-        case KVM_CAP_DESTROY_MEMORY_REGION_WORKS:
-        case KVM_CAP_JOIN_MEMORY_REGIONS_WORKS:
-#ifdef CONFIG_KVM_APIC_ARCHITECTURE
-        case KVM_CAP_SET_BOOT_CPU_ID:
-#endif
-        case KVM_CAP_INTERNAL_ERROR_DATA:
-#ifdef CONFIG_HAVE_KVM_MSI
-        case KVM_CAP_SIGNAL_MSI:
-#endif
-#ifdef CONFIG_HAVE_KVM_IRQ_ROUTING
-        case KVM_CAP_IRQFD_RESAMPLE:
-#endif
-                return 1;
-#ifdef CONFIG_HAVE_KVM_IRQ_ROUTING
-        case KVM_CAP_IRQ_ROUTING:
-                return KVM_MAX_IRQ_ROUTES;
-#endif
-        default:
-                break;
-        }
-        return kvm_vm_ioctl_check_extension(kvm, arg);
-}
-
 static long kvm_dev_ioctl(struct file *filp,
                           unsigned int ioctl, unsigned long arg)
 {