KVM: PPC: Book3S HV: Add NO_HASH flag to GET_SMMU_INFO ioctl result

This adds a KVM_PPC_NO_HASH flag to the flags field of the
kvm_ppc_smmu_info struct, and arranges for it to be set when
running as a nested hypervisor, as an unambiguous indication
to userspace that HPT guests are not supported.  Reporting the
KVM_CAP_PPC_MMU_HASH_V3 capability as false could be taken as
indicating only that the new HPT features in ISA V3.0 are not
supported, leaving it ambiguous whether pre-V3.0 HPT features
are supported.

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

Documentation/virtual/kvm/api.txt

@@ -2270,6 +2270,10 @@ The supported flags are:
         The emulated MMU supports 1T segments in addition to the
         standard 256M ones.
 
+    - KVM_PPC_NO_HASH
+	This flag indicates that HPT guests are not supported by KVM,
+	thus all guests must use radix MMU mode.
+
 The "slb_size" field indicates how many SLB entries are supported
 
 The "sps" array contains 8 entries indicating the supported base

arch/powerpc/kvm/book3s_hv.c

@@ -4257,6 +4257,10 @@ static int kvm_vm_ioctl_get_smmu_info_hv(struct kvm *kvm,
 	kvmppc_add_seg_page_size(&sps, 16, SLB_VSID_L | SLB_VSID_LP_01);
 	kvmppc_add_seg_page_size(&sps, 24, SLB_VSID_L);
 
+	/* If running as a nested hypervisor, we don't support HPT guests */
+	if (kvmhv_on_pseries())
+		info->flags |= KVM_PPC_NO_HASH;
+
 	return 0;
 }
 

include/uapi/linux/kvm.h

@@ -719,6 +719,7 @@ struct kvm_ppc_one_seg_page_size {
 
 #define KVM_PPC_PAGE_SIZES_REAL		0x00000001
 #define KVM_PPC_1T_SEGMENTS		0x00000002
+#define KVM_PPC_NO_HASH			0x00000004
 
 struct kvm_ppc_smmu_info {
 	__u64 flags;