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>

3 files changed, 9 insertions, 0 deletions

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index fde48b6708f1..df98b6304769 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/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
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 89bcf923d542..788bc61bd08c 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/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;
 }
 
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index d9cec6b5cb37..7f2ff3a76995 100644
--- a/include/uapi/linux/kvm.h
+++ b/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;