[Qemu-devel] [PATCH qemu] spapr/target-ppc/kvm: Only add hcall-instructions if KVM supports it

[Alexey Kardashevskiy <aik@ozlabs.ru>]

ePAPR defines "hcall-instructions" device-tree property which contains
code to call hypercalls in ePAPR paravirtualized guests. However this
property is also present for pseries guests where it does not make sense,
even though it contains dummy code which simply fails.

Instead of maintaining the property (which used to be BE only; then was
fixed to be endian-agnostic) and confusing the guest (which might think
there is ePAPR host while there is none), this simply does not
the property to the device tree if the host kernel does not implement it.

In order to tell the machine code if the host kernel supports
KVM_CAP_PPC_GET_PVINFO, this changes kvmppc_get_hypercall() to return 1
if the host kernel does not implement it (which is HV KVM case).

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---


Alexander,

We just got a bug report that LE guests would not boot under quite old QEMU
and we (powerkvm) wonder if it makes sense to backport endian-agnostic
hypercall code to older QEMU or it is simpler/more correct
not to have epapr-hypercall property in the tree.


---
 hw/ppc/spapr.c   | 9 +++++----
 target-ppc/kvm.c | 2 +-
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 43708a2..8130eb4 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -497,10 +497,11 @@ static void *spapr_create_fdt_skel(hwaddr initrd_base,
              * Older KVM versions with older guest kernels were broken with the
              * magic page, don't allow the guest to map it.
              */
-            kvmppc_get_hypercall(first_cpu->env_ptr, hypercall,
-                                 sizeof(hypercall));
-            _FDT((fdt_property(fdt, "hcall-instructions", hypercall,
-                              sizeof(hypercall))));
+            if (!kvmppc_get_hypercall(first_cpu->env_ptr, hypercall,
+                                      sizeof(hypercall))) {
+                _FDT((fdt_property(fdt, "hcall-instructions", hypercall,
+                                   sizeof(hypercall))));
+            }
         }
         _FDT((fdt_end_node(fdt)));
     }
diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c
index 776336b..e5183db 100644
--- a/target-ppc/kvm.c
+++ b/target-ppc/kvm.c
@@ -2001,7 +2001,7 @@ int kvmppc_get_hypercall(CPUPPCState *env, uint8_t *buf, int buf_len)
     hc[2] = cpu_to_be32(0x48000008);
     hc[3] = cpu_to_be32(bswap32(0x3860ffff));
 
-    return 0;
+    return 1;
 }
 
 static inline int kvmppc_enable_hcall(KVMState *s, target_ulong hcall)
-- 
2.5.0.rc3