Nested KVM HV only works if the kernel is using the radix MMU mode, ie.
the CPU is POWER9 and it is not running in some pre-power9 compat mode.
Otherwise, the KVM HV module fails to load in the guest with -ENODEV.
It might be painful for a user to discover this late that nested cannot
work with their setup. Erroring out at machine init instead seems to be
the best we can do.

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
---
 hw/ppc/spapr_caps.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
index 275f5bd0342c..10a80a8159f4 100644
--- a/hw/ppc/spapr_caps.c
+++ b/hw/ppc/spapr_caps.c
@@ -382,6 +382,8 @@ static void cap_nested_kvm_hv_apply(SpaprMachineState *spapr,
                                     uint8_t val, Error **errp)
 {
     ERRP_GUARD();
+    PowerPCCPU *cpu = POWERPC_CPU(first_cpu);
+
     if (!val) {
         /* capability disabled by default */
         return;
@@ -391,6 +393,14 @@ static void cap_nested_kvm_hv_apply(SpaprMachineState *spapr,
         error_setg(errp, "No Nested KVM-HV support in TCG");
         error_append_hint(errp, "Try appending -machine cap-nested-hv=off\n");
     } else if (kvm_enabled()) {
+        if (!ppc_check_compat(cpu, CPU_POWERPC_LOGICAL_3_00, 0,
+                              spapr->max_compat_pvr)) {
+            error_setg(errp, "Nested KVM-HV only supported on POWER9");
+            error_append_hint(errp,
+                              "Try appending -machine max-cpu-compat=power9\n");
+            return;
+        }
+
         if (!kvmppc_has_cap_nested_kvm_hv()) {
             error_setg(errp,
                        "KVM implementation does not support Nested KVM-HV");

On Thu, Jul 16, 2020 at 07:11:21PM +0200, Greg Kurz wrote:
> Nested KVM HV only works if the kernel is using the radix MMU mode, ie.
> the CPU is POWER9 and it is not running in some pre-power9 compat mode.
> Otherwise, the KVM HV module fails to load in the guest with -ENODEV.
> It might be painful for a user to discover this late that nested cannot
> work with their setup. Erroring out at machine init instead seems to be
> the best we can do.
> 
> Signed-off-by: Greg Kurz <groug@kaod.org>
> Reviewed-by: Laurent Vivier <lvivier@redhat.com>

Applied to ppc-for-5.2.

> ---
>  hw/ppc/spapr_caps.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
> index 275f5bd0342c..10a80a8159f4 100644
> --- a/hw/ppc/spapr_caps.c
> +++ b/hw/ppc/spapr_caps.c
> @@ -382,6 +382,8 @@ static void cap_nested_kvm_hv_apply(SpaprMachineState *spapr,
>                                      uint8_t val, Error **errp)
>  {
>      ERRP_GUARD();
> +    PowerPCCPU *cpu = POWERPC_CPU(first_cpu);
> +
>      if (!val) {
>          /* capability disabled by default */
>          return;
> @@ -391,6 +393,14 @@ static void cap_nested_kvm_hv_apply(SpaprMachineState *spapr,
>          error_setg(errp, "No Nested KVM-HV support in TCG");
>          error_append_hint(errp, "Try appending -machine cap-nested-hv=off\n");
>      } else if (kvm_enabled()) {
> +        if (!ppc_check_compat(cpu, CPU_POWERPC_LOGICAL_3_00, 0,
> +                              spapr->max_compat_pvr)) {
> +            error_setg(errp, "Nested KVM-HV only supported on POWER9");
> +            error_append_hint(errp,
> +                              "Try appending -machine max-cpu-compat=power9\n");
> +            return;
> +        }
> +
>          if (!kvmppc_has_cap_nested_kvm_hv()) {
>              error_setg(errp,
>                         "KVM implementation does not support Nested KVM-HV");
> 
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson