xen/m2p: No need to catch exceptions when we know that there is no RAM

.. beyound what we think is the end of memory. However there might
be more System RAM - but assigned to a guest. Hence jump to the
M2P override check and consult.

[v1: Added Review-by tag]

Reviewed-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
index 78ebbeb88d9c..195707060493 100644
--- a/arch/x86/include/asm/xen/page.h
+++ b/arch/x86/include/asm/xen/page.h
@@ -85,6 +85,10 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
         if (xen_feature(XENFEAT_auto_translated_physmap))
                 return mfn;
 
+        if (unlikely((mfn >> machine_to_phys_order) != 0)) {
+                pfn = ~0;
+                goto try_override;
+        }
         pfn = 0;
         /*
          * The array access can fail (e.g., device space beyond end of RAM).
@@ -92,7 +96,7 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
          * but we must handle the fault without crashing!
          */
         __get_user(pfn, &machine_to_phys_mapping[mfn]);
-
+try_override:
         /*
          * If this appears to be a foreign mfn (because the pfn
          * doesn't map back to the mfn), then check the local override