[Xen-devel] [PATCH] x86: Address "Bitwise-and with zero CONSTANT_EXPRESSION_RESULT" Coverity issues

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Coverity complains at code which which performs a bitwise and with a constant
that happens to be zero.  Both _PAGE_GNTTAB and PG_SH_enable may be 0
depending on Kconfig settings.

Rearrange the C to test the constant first and short circuit the bitwise and.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Tim Deegan <tim@xxxxxxx>
CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
---
 xen/arch/x86/mm.c            | 2 +-
 xen/include/asm-x86/paging.h | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 2b74392..8d1120a 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -1225,7 +1225,7 @@ void put_page_from_l1e(l1_pgentry_t l1e, struct domain 
*l1e_owner)
      * (Note that the undestroyable active grants are not a security hole in
      * Xen. All active grants can safely be cleaned up when the domain dies.)
      */
-    if ( (l1e_get_flags(l1e) & _PAGE_GNTTAB) &&
+    if ( _PAGE_GNTTAB && (l1e_get_flags(l1e) & _PAGE_GNTTAB) &&
          !l1e_owner->is_shutting_down && !l1e_owner->is_dying )
     {
         gdprintk(XENLOG_WARNING,
diff --git a/xen/include/asm-x86/paging.h b/xen/include/asm-x86/paging.h
index f008551..f0b6705 100644
--- a/xen/include/asm-x86/paging.h
+++ b/xen/include/asm-x86/paging.h
@@ -61,7 +61,8 @@
 #define PG_MASK (PG_refcounts | PG_log_dirty | PG_translate | PG_external)
 
 #define paging_mode_enabled(_d)   (!!(_d)->arch.paging.mode)
-#define paging_mode_shadow(_d)    (!!((_d)->arch.paging.mode & PG_SH_enable))
+#define paging_mode_shadow(_d)    (PG_SH_enable && \
+                                   !!((_d)->arch.paging.mode & PG_SH_enable))
 #define paging_mode_hap(_d)       (!!((_d)->arch.paging.mode & PG_HAP_enable))
 
 #define paging_mode_refcounts(_d) (!!((_d)->arch.paging.mode & PG_refcounts))
-- 
2.1.4


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