[PATCH for-4.15] x86/dmop: Properly fail for PV guests

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

The current code has an early exit for PV guests, but it returns 0 having done
nothing.

Fixes: 524a98c2ac5 ("public / x86: introduce __HYPERCALL_dm_op...")
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Ian Jackson <iwj@xxxxxxxxxxxxxx>
CC: Paul Durrant <paul@xxxxxxx>

For 4.15.  Found while testing XEN_DMOP_nr_vcpus.  Needs backporting to all
stable releases.
---
 xen/arch/x86/hvm/dm.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/xen/arch/x86/hvm/dm.c b/xen/arch/x86/hvm/dm.c
index 5bc172a5d4..612749442e 100644
--- a/xen/arch/x86/hvm/dm.c
+++ b/xen/arch/x86/hvm/dm.c
@@ -365,6 +365,7 @@ int dm_op(const struct dmop_args *op_args)
     if ( rc )
         return rc;
 
+    rc = -EINVAL;
     if ( !is_hvm_domain(d) )
         goto out;
 
-- 
2.11.0