KVM: PPC: Add CAP to indicate hcall fixes

We worked around some nasty KVM magic page hcall breakages:

  1) NX bit not honored, so ignore NX when we detect it
  2) LE guests swizzle hypercall instruction

Without these fixes in place, there's no way it would make sense to expose kvm
hypercalls to a guest. Chances are immensely high it would trip over and break.

So add a new CAP that gives user space a hint that we have workarounds for the
bugs above in place. It can use those as hint to disable PV hypercalls when
the guest CPU is anything POWER7 or higher and the host does not have fixes
in place.

Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/kvm/powerpc.c

@@ -416,6 +416,7 @@ int kvm_dev_ioctl_check_extension(long ext)
 	case KVM_CAP_SPAPR_TCE:
 	case KVM_CAP_PPC_ALLOC_HTAB:
 	case KVM_CAP_PPC_RTAS:
+	case KVM_CAP_PPC_FIXUP_HCALL:
 #ifdef CONFIG_KVM_XICS
 	case KVM_CAP_IRQ_XICS:
 #endif

include/uapi/linux/kvm.h

@@ -748,6 +748,7 @@ struct kvm_ppc_smmu_info {
 #define KVM_CAP_S390_IRQCHIP 99
 #define KVM_CAP_IOEVENTFD_NO_LENGTH 100
 #define KVM_CAP_VM_ATTRIBUTES 101
+#define KVM_CAP_PPC_FIXUP_HCALL 102
 
 #ifdef KVM_CAP_IRQ_ROUTING