x86: fix off-by-one in is_xen_fixed_mfn()

__2M_rwdata_end marks the first byte after the Xen image, not its last
byte. Subtract 1 to obtain the upper bound to compare against. (Note
that instead switching from <= to < is less desirable, as in principle
__pa() might return rubbish for addresses outside of the Xen image.)

Since the & needs to be dropped from the line in question, also drop it
from the adjacent one.

Reported-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 9633929824
master date: 2019-10-25 10:38:58 +0200

xen/include/asm-x86/mm.h

@@ -295,8 +295,8 @@ struct page_info
 #define is_xen_heap_mfn(mfn) \
     (__mfn_valid(mfn) && is_xen_heap_page(mfn_to_page(_mfn(mfn))))
 #define is_xen_fixed_mfn(mfn)                     \
-    ((((mfn) << PAGE_SHIFT) >= __pa(&_stext)) &&  \
-     (((mfn) << PAGE_SHIFT) <= __pa(&__2M_rwdata_end)))
+    ((((mfn) << PAGE_SHIFT) >= __pa(_stext)) &&  \
+     (((mfn) << PAGE_SHIFT) <= __pa(__2M_rwdata_end - 1)))
 
 #define PRtype_info "016lx"/* should only be used for printk's */