x86: make certain memory sub-ops return valid values

When a domain's shared info field "max_pfn" is zero,
domain_get_maximum_gpfn() so far returned ULONG_MAX, which
do_memory_op() in turn converted to -1 (i.e. -EPERM). Make the former
always return a sensible number (i.e. zero if the field was zero) and
have the latter no longer truncate return values.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/xen/common/compat/memory.c b/xen/common/compat/memory.c
index caa24ccbe6..ba7e6eb0b9 100644
--- a/xen/common/compat/memory.c
+++ b/xen/common/compat/memory.c
@@ -15,7 +15,8 @@ CHECK_TYPE(domid);
 
 int compat_memory_op(unsigned int cmd, XEN_GUEST_HANDLE_PARAM(void) compat)
 {
-    int rc, split, op = cmd & MEMOP_CMD_MASK;
+    int split, op = cmd & MEMOP_CMD_MASK;
+    long rc;
     unsigned int start_extent = cmd >> MEMOP_EXTENT_SHIFT;
 
     do
@@ -204,7 +205,7 @@ int compat_memory_op(unsigned int cmd, XEN_GUEST_HANDLE_PARAM(void) compat)
 
         rc = do_memory_op(cmd, nat.hnd);
         if ( rc < 0 )
-            return rc;
+            break;
 
         cmd = 0;
         if ( hypercall_xlat_continuation(&cmd, 0x02, nat.hnd, compat) )
@@ -326,5 +327,11 @@ int compat_memory_op(unsigned int cmd, XEN_GUEST_HANDLE_PARAM(void) compat)
                 __HYPERVISOR_memory_op, "ih", cmd, compat);
     } while ( split > 0 );
 
+    if ( unlikely(rc > INT_MAX) )
+        return INT_MAX;
+
+    if ( unlikely(rc < INT_MIN) )
+        return INT_MIN;
+
     return rc;
 }