mem_access: fix setting default mem_access type

When xc_hvm_set_mem_access(xch, domain_id, default_access, ~0ull, 0)
is called, first_pfn=~0ull is a hint to HVMOP_set_mem_access as to
what the default mem_access type is for the domain. This call was
failing because it was gated by the memory range check in the
HVMOP_set_mem_access case statement in do_hvm_op(). The following
patch fixes this issue.

Signed-off-by: Aravindh Puthiyaparambil <aravindh@virtuata.com>
Acked-by: Tim Deegan <tim@xen.org>
Committed-by: Tim Deegan <tim@xen.org>

---
 xen/arch/x86/hvm/hvm.c |  5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

xen/arch/x86/hvm/hvm.c

@@ -4195,9 +4195,10 @@ long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE(void) arg)
             goto param_fail5;
 
         rc = -EINVAL;
-        if ( (a.first_pfn > domain_get_maximum_gpfn(d)) ||
+        if ( (a.first_pfn != ~0ull) &&
+             ((a.first_pfn > domain_get_maximum_gpfn(d)) ||
              ((a.first_pfn + a.nr - 1) < a.first_pfn) ||
-             ((a.first_pfn + a.nr - 1) > domain_get_maximum_gpfn(d)) )
+             ((a.first_pfn + a.nr - 1) > domain_get_maximum_gpfn(d))) )
             goto param_fail5;
             
         rc = p2m_set_mem_access(d, a.first_pfn, a.nr, a.hvmmem_access);