[Qemu-devel] [PATCH 1/3] ppc: Correctly handle errors reading ibm, vmx and ibm, dfp properties

[David Gibson <david@gibson.dropbear.id.au>]

kvmppc_read_int_cpu_dt() returns -1 on errors. However
kvmppc_host_cpu_def() assumes that it can use the return value
directly for setting the corresponding instruction support bits.  This
will give invalid results when kvmppc_read_int_cpu_dt() returns -1
(i.e. 0xffffffff).

In fact, it gets worse: the common case for -1 return values is when
the properties are simply not present.  On some machines this means
the features are not available but in other cases it just means that
the firmware on this platform does not provide this information.  So,
when there's an error reading the properties we really can't tell if
vmx or dfp is supported.

Therefore, this patch checks for -1 return values and falls back to
qemu's built in table of CPU capabilities in that case.

Reported-by: Nishanth Aravamudan <nacc@us.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 target-ppc/kvm.c |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c
index a090d79..6b156be 100644
--- a/target-ppc/kvm.c
+++ b/target-ppc/kvm.c
@@ -912,9 +912,13 @@ const ppc_def_t *kvmppc_host_cpu_def(void)
 
     /* Now fix up the spec with information we can query from the host */
 
-    alter_insns(&spec->insns_flags, PPC_ALTIVEC, vmx > 0);
-    alter_insns(&spec->insns_flags2, PPC2_VSX, vmx > 1);
-    alter_insns(&spec->insns_flags2, PPC2_DFP, dfp);
+    if (vmx != -1) {
+        alter_insns(&spec->insns_flags, PPC_ALTIVEC, vmx > 0);
+        alter_insns(&spec->insns_flags2, PPC2_VSX, vmx > 1);
+    }
+    if (dfp != -1) {
+        alter_insns(&spec->insns_flags2, PPC2_DFP, dfp);
+    }
 
     return spec;
 }
-- 
1.7.7