common: guard iommu symbols with CONFIG_HAS_PASSTHROUGH

The variables iommu_enabled and iommu_dont_flush_iotlb are defined in
drivers/passthrough/iommu.c and are referenced in common code, which
causes the link to fail when !CONFIG_HAS_PASSTHROUGH.

Guard references to these variables in common code so that xen
builds when !CONFIG_HAS_PASSTHROUGH.
Signed-off-by: Connor Davis <connojdavis@gmail.com>
[jb: further massage xen/iommu.h adjustment]
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/common/memory.c

@@ -294,7 +294,9 @@ int guest_remove_page(struct domain *d, unsigned long gmfn)
     p2m_type_t p2mt;
 #endif
     mfn_t mfn;
+#ifdef CONFIG_HAS_PASSTHROUGH
     bool *dont_flush_p, dont_flush;
+#endif
     int rc;
 
 #ifdef CONFIG_X86
@@ -385,13 +387,17 @@ int guest_remove_page(struct domain *d, unsigned long gmfn)
      * Since we're likely to free the page below, we need to suspend
      * xenmem_add_to_physmap()'s suppressing of IOMMU TLB flushes.
      */
+#ifdef CONFIG_HAS_PASSTHROUGH
     dont_flush_p = &this_cpu(iommu_dont_flush_iotlb);
     dont_flush = *dont_flush_p;
     *dont_flush_p = false;
+#endif
 
     rc = guest_physmap_remove_page(d, _gfn(gmfn), mfn, 0);
 
+#ifdef CONFIG_HAS_PASSTHROUGH
     *dont_flush_p = dont_flush;
+#endif
 
     /*
      * With the lack of an IOMMU on some platforms, domains with DMA-capable
@@ -839,11 +845,13 @@ int xenmem_add_to_physmap(struct domain *d, struct xen_add_to_physmap *xatp,
     xatp->gpfn += start;
     xatp->size -= start;
 
+#ifdef CONFIG_HAS_PASSTHROUGH
     if ( is_iommu_enabled(d) )
     {
        this_cpu(iommu_dont_flush_iotlb) = 1;
        extra.ppage = &pages[0];
     }
+#endif
 
     while ( xatp->size > done )
     {
@@ -868,6 +876,7 @@ int xenmem_add_to_physmap(struct domain *d, struct xen_add_to_physmap *xatp,
         }
     }
 
+#ifdef CONFIG_HAS_PASSTHROUGH
     if ( is_iommu_enabled(d) )
     {
         int ret;
@@ -894,6 +903,7 @@ int xenmem_add_to_physmap(struct domain *d, struct xen_add_to_physmap *xatp,
         if ( unlikely(ret) && rc >= 0 )
             rc = ret;
     }
+#endif
 
     return rc;
 }

xen/include/xen/iommu.h

@@ -51,8 +51,12 @@ static inline bool_t dfn_eq(dfn_t x, dfn_t y)
     return dfn_x(x) == dfn_x(y);
 }
 
+#ifdef CONFIG_HAS_PASSTHROUGH
 extern bool_t iommu_enable, iommu_enabled;
 extern bool force_iommu, iommu_quarantine, iommu_verbose;
+#else
+#define iommu_enabled false
+#endif
 
 #ifdef CONFIG_X86
 extern enum __packed iommu_intremap {