[PATCH] KVM: PPC: Book3S HV: Fix L2 guest reboot failure due to empty 'arch_compat'

[Amit Machhiwal <amachhiw@xxxxxxxxxxxxx>]

Currently, rebooting a pseries nested qemu-kvm guest (L2) results in
below error as L1 qemu sends PVR value 'arch_compat' == 0 via
ppc_set_compat ioctl. This triggers a condition failure in
kvmppc_set_arch_compat() resulting in an EINVAL.

qemu-system-ppc64: Unable to set CPU compatibility mode in KVM: Invalid

This patch updates kvmppc_set_arch_compat() to use the host PVR value if
'compat_pvr' == 0 indicating that qemu doesn't want to enforce any
specific PVR compat mode.

Signed-off-by: Amit Machhiwal <amachhiw@xxxxxxxxxxxxx>
---
 arch/powerpc/kvm/book3s_hv.c          |  2 +-
 arch/powerpc/kvm/book3s_hv_nestedv2.c | 12 ++++++++++--
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 1ed6ec140701..9573d7f4764a 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -439,7 +439,7 @@ static int kvmppc_set_arch_compat(struct kvm_vcpu *vcpu, u32 arch_compat)
 	if (guest_pcr_bit > host_pcr_bit)
 		return -EINVAL;
 
-	if (kvmhv_on_pseries() && kvmhv_is_nestedv2()) {
+	if (kvmhv_on_pseries() && kvmhv_is_nestedv2() && arch_compat) {
 		if (!(cap & nested_capabilities))
 			return -EINVAL;
 	}
diff --git a/arch/powerpc/kvm/book3s_hv_nestedv2.c b/arch/powerpc/kvm/book3s_hv_nestedv2.c
index fd3c4f2d9480..069a1fcfd782 100644
--- a/arch/powerpc/kvm/book3s_hv_nestedv2.c
+++ b/arch/powerpc/kvm/book3s_hv_nestedv2.c
@@ -138,6 +138,7 @@ static int gs_msg_ops_vcpu_fill_info(struct kvmppc_gs_buff *gsb,
 	vector128 v;
 	int rc, i;
 	u16 iden;
+	u32 arch_compat = 0;
 
 	vcpu = gsm->data;
 
@@ -347,8 +348,15 @@ static int gs_msg_ops_vcpu_fill_info(struct kvmppc_gs_buff *gsb,
 			break;
 		}
 		case KVMPPC_GSID_LOGICAL_PVR:
-			rc = kvmppc_gse_put_u32(gsb, iden,
-						vcpu->arch.vcore->arch_compat);
+			if (!vcpu->arch.vcore->arch_compat) {
+				if (cpu_has_feature(CPU_FTR_ARCH_31))
+					arch_compat = PVR_ARCH_31;
+				else if (cpu_has_feature(CPU_FTR_ARCH_300))
+					arch_compat = PVR_ARCH_300;
+			} else {
+				arch_compat = vcpu->arch.vcore->arch_compat;
+			}
+			rc = kvmppc_gse_put_u32(gsb, iden, arch_compat);
 			break;
 		}
 
-- 
2.43.0