Some of the uses of dom_cow aren't easily DCE-able (without extra
#ifdef-ary), and hence it being constantly NULL when MEM_SHARING=n
misguides Coverity into thinking that there may be a NULL deref in
if ( p2m_is_shared(t) )
d = dom_cow;
if ( get_page(page, d) )
return page;
(in get_page_from_mfn_and_type()). Help the situation by making
p2m_is_shared() be compile-time false when MEM_SHARING=n, thus also
permitting the compiler to DCE some other code.
Note that p2m_is_sharable() isn't used outside of mem_sharing.c, and
hence P2M_SHARABLE_TYPES can simply be left undefined when
MEM_SHARING=n.
Coverity ID: 1645573
Fixes: 79d91e178a1a ("dom_cow is needed for mem-sharing only")
Signed-off-by: Jan Beulich <jbeul...@suse.com>
---
Might be nice to also eliminate p2m_ram_shared (and for MEM_PAGING=n
also the three paging types) entirely from such builds, to eliminate the
risk of accidental use. Yet that would apparently also come at the price
of more #ifdef-ary. Opinions?
--- a/xen/arch/x86/include/asm/p2m.h
+++ b/xen/arch/x86/include/asm/p2m.h
@@ -136,11 +136,16 @@ typedef unsigned int p2m_query_t;
#endif
/* Shared types */
+#ifdef CONFIG_MEM_SHARING
/* XXX: Sharable types could include p2m_ram_ro too, but we would need to
* reinit the type correctly after fault */
#define P2M_SHARABLE_TYPES (p2m_to_mask(p2m_ram_rw) \
| p2m_to_mask(p2m_ram_logdirty) )
#define P2M_SHARED_TYPES (p2m_to_mask(p2m_ram_shared))
+#else
+/* P2M_SHARABLE_TYPES deliberately not provided. */
+#define P2M_SHARED_TYPES 0
+#endif
/* Types established/cleaned up via special accessors. */
#define P2M_SPECIAL_TYPES (P2M_GRANT_TYPES | \
