x86: re-arrange struct page_info members

By combining the overlay fields that are 8 bytes long (on x86-64) into
a union separate from the one used for the 4 byte wide fields, no
unnecessary padding will be inserted while at the same time avoiding
to use __attribute__((__packed__)) on any of the sub-structures (which
risks misaligning structure members without immediately noticing).

Signed-off-by: Jan Beulich <jbeulich@novell.com>

xen/arch/x86/mm/shadow/common.c

@@ -1334,7 +1334,7 @@ static inline void trace_shadow_prealloc_unpin(struct domain *d, mfn_t smfn)
         /* Convert smfn to gfn */
         unsigned long gfn;
         ASSERT(mfn_valid(smfn));
-        gfn = mfn_to_gfn(d, _mfn(mfn_to_shadow_page(smfn)->u.sh.back));
+        gfn = mfn_to_gfn(d, _mfn(mfn_to_shadow_page(smfn)->v.sh.back));
         __trace_var(TRC_SHADOW_PREALLOC_UNPIN, 0/*!tsc*/,
                     sizeof(gfn), (unsigned char*)&gfn);
     }
@@ -1542,7 +1542,7 @@ mfn_t shadow_alloc(struct domain *d,
     while ( i != order )
     {
         i--;
-        sp->u.sh.order = i;
+        sp->v.free.order = i;
         page_list_add_tail(sp, &d->arch.paging.shadow.freelists[i]);
         sp += 1 << i;
     }
@@ -1569,7 +1569,7 @@ mfn_t shadow_alloc(struct domain *d,
         sp[i].u.sh.type = shadow_type;
         sp[i].u.sh.pinned = 0;
         sp[i].u.sh.count = 0;
-        sp[i].u.sh.back = backpointer;
+        sp[i].v.sh.back = backpointer;
         set_next_shadow(&sp[i], NULL);
         perfc_incr(shadow_alloc_count);
     }
@@ -1629,20 +1629,20 @@ void shadow_free(struct domain *d, mfn_t smfn)
         if ( (mfn_x(shadow_page_to_mfn(sp)) & mask) ) {
             /* Merge with predecessor block? */
             if ( ((sp-mask)->u.sh.type != PGT_none) ||
-                 ((sp-mask)->u.sh.order != order) )
+                 ((sp-mask)->v.free.order != order) )
                 break;
             sp -= mask;
             page_list_del(sp, &d->arch.paging.shadow.freelists[order]);
         } else {
             /* Merge with successor block? */
             if ( ((sp+mask)->u.sh.type != PGT_none) ||
-                 ((sp+mask)->u.sh.order != order) )
+                 ((sp+mask)->v.free.order != order) )
                 break;
             page_list_del(sp + mask, &d->arch.paging.shadow.freelists[order]);
         }
     }
 
-    sp->u.sh.order = order;
+    sp->v.free.order = order;
     page_list_add_tail(sp, &d->arch.paging.shadow.freelists[order]);
 }
 
@@ -1825,7 +1825,7 @@ static unsigned int sh_set_allocation(struct domain *d,
                 sp[j].u.sh.count = 0;
                 sp[j].tlbflush_timestamp = 0; /* Not in any TLB */
             }
-            sp->u.sh.order = order;
+            sp->v.free.order = order;
             page_list_add_tail(sp, &d->arch.paging.shadow.freelists[order]);
         } 
         else if ( d->arch.paging.shadow.total_pages > pages ) 
@@ -1904,17 +1904,17 @@ static void sh_hash_audit_bucket(struct domain *d, int bucket)
         BUG_ON( sp->u.sh.type == 0 );
         BUG_ON( sp->u.sh.type > SH_type_max_shadow );
         /* Wrong bucket? */
-        BUG_ON( sh_hash(sp->u.sh.back, sp->u.sh.type) != bucket );
+        BUG_ON( sh_hash(sp->v.sh.back, sp->u.sh.type) != bucket );
         /* Duplicate entry? */
         for ( x = next_shadow(sp); x; x = next_shadow(x) )
-            BUG_ON( x->u.sh.back == sp->u.sh.back &&
+            BUG_ON( x->v.sh.back == sp->v.sh.back &&
                     x->u.sh.type == sp->u.sh.type );
         /* Follow the backpointer to the guest pagetable */
         if ( sp->u.sh.type != SH_type_fl1_32_shadow
              && sp->u.sh.type != SH_type_fl1_pae_shadow
              && sp->u.sh.type != SH_type_fl1_64_shadow )
         {
-            struct page_info *gpg = mfn_to_page(_mfn(sp->u.sh.back));
+            struct page_info *gpg = mfn_to_page(_mfn(sp->v.sh.back));
             /* Bad shadow flags on guest page? */
             BUG_ON( !(gpg->shadow_flags & (1<<sp->u.sh.type)) );
             /* Bad type count on guest page? */
@@ -1930,7 +1930,7 @@ static void sh_hash_audit_bucket(struct domain *d, int bucket)
                     {
                         SHADOW_ERROR("MFN %#"PRpgmfn" shadowed (by %#"PRI_mfn")"
                                      " and not OOS but has typecount %#lx\n",
-                                     sp->u.sh.back,
+                                     sp->v.sh.back,
                                      mfn_x(shadow_page_to_mfn(sp)), 
                                      gpg->u.inuse.type_info);
                         BUG();
@@ -1944,7 +1944,7 @@ static void sh_hash_audit_bucket(struct domain *d, int bucket)
             {
                 SHADOW_ERROR("MFN %#"PRpgmfn" shadowed (by %#"PRI_mfn")"
                              " but has typecount %#lx\n",
-                             sp->u.sh.back, mfn_x(shadow_page_to_mfn(sp)),
+                             sp->v.sh.back, mfn_x(shadow_page_to_mfn(sp)),
                              gpg->u.inuse.type_info);
                 BUG();
             }
@@ -2030,7 +2030,7 @@ mfn_t shadow_hash_lookup(struct vcpu *v, unsigned long n, unsigned int t)
     prev = NULL;
     while(sp)
     {
-        if ( sp->u.sh.back == n && sp->u.sh.type == t )
+        if ( sp->v.sh.back == n && sp->u.sh.type == t )
         {
             /* Pull-to-front if 'sp' isn't already the head item */
             if ( unlikely(sp != d->arch.paging.shadow.hash_table[key]) )
@@ -2197,7 +2197,7 @@ void sh_destroy_shadow(struct vcpu *v, mfn_t smfn)
            t == SH_type_fl1_64_shadow  || 
            t == SH_type_monitor_table  || 
            (is_pv_32on64_vcpu(v) && t == SH_type_l4_64_shadow) ||
-           (page_get_owner(mfn_to_page(_mfn(sp->u.sh.back)))
+           (page_get_owner(mfn_to_page(_mfn(sp->v.sh.back)))
             == v->domain)); 
 
     /* The down-shifts here are so that the switch statement is on nice

xen/arch/x86/mm/shadow/multi.c

@@ -974,7 +974,7 @@ static int shadow_set_l2e(struct vcpu *v,
 #if (SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC)
         {
             struct shadow_page_info *sp = mfn_to_shadow_page(sl1mfn);
-            mfn_t gl1mfn = _mfn(sp->u.sh.back);
+            mfn_t gl1mfn = _mfn(sp->v.sh.back);
 
             /* If the shadow is a fl1 then the backpointer contains
                the GFN instead of the GMFN, and it's definitely not
@@ -1926,7 +1926,7 @@ void sh_destroy_l4_shadow(struct vcpu *v, mfn_t smfn)
     ASSERT(t == SH_type_l4_shadow);
 
     /* Record that the guest page isn't shadowed any more (in this type) */
-    gmfn = _mfn(mfn_to_shadow_page(smfn)->u.sh.back);
+    gmfn = _mfn(mfn_to_shadow_page(smfn)->v.sh.back);
     delete_shadow_status(v, gmfn, t, smfn);
     shadow_demote(v, gmfn, t);
     /* Decrement refcounts of all the old entries */
@@ -1955,7 +1955,7 @@ void sh_destroy_l3_shadow(struct vcpu *v, mfn_t smfn)
     ASSERT(t == SH_type_l3_shadow);
 
     /* Record that the guest page isn't shadowed any more (in this type) */
-    gmfn = _mfn(mfn_to_shadow_page(smfn)->u.sh.back);
+    gmfn = _mfn(mfn_to_shadow_page(smfn)->v.sh.back);
     delete_shadow_status(v, gmfn, t, smfn);
     shadow_demote(v, gmfn, t);
 
@@ -1990,7 +1990,7 @@ void sh_destroy_l2_shadow(struct vcpu *v, mfn_t smfn)
 #endif
 
     /* Record that the guest page isn't shadowed any more (in this type) */
-    gmfn = _mfn(mfn_to_shadow_page(smfn)->u.sh.back);
+    gmfn = _mfn(mfn_to_shadow_page(smfn)->v.sh.back);
     delete_shadow_status(v, gmfn, t, smfn);
     shadow_demote(v, gmfn, t);
 
@@ -2020,12 +2020,12 @@ void sh_destroy_l1_shadow(struct vcpu *v, mfn_t smfn)
     /* Record that the guest page isn't shadowed any more (in this type) */
     if ( t == SH_type_fl1_shadow )
     {
-        gfn_t gfn = _gfn(mfn_to_shadow_page(smfn)->u.sh.back);
+        gfn_t gfn = _gfn(mfn_to_shadow_page(smfn)->v.sh.back);
         delete_fl1_shadow_status(v, gfn, smfn);
     }
     else 
     {
-        mfn_t gmfn = _mfn(mfn_to_shadow_page(smfn)->u.sh.back);
+        mfn_t gmfn = _mfn(mfn_to_shadow_page(smfn)->v.sh.back);
         delete_shadow_status(v, gmfn, t, smfn);
         shadow_demote(v, gmfn, t);
     }
@@ -2349,7 +2349,7 @@ static int validate_gl1e(struct vcpu *v, void *new_ge, mfn_t sl1mfn, void *se)
     result |= shadow_set_l1e(v, sl1p, new_sl1e, sl1mfn);
 
 #if (SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC)
-    gl1mfn = _mfn(mfn_to_shadow_page(sl1mfn)->u.sh.back);
+    gl1mfn = _mfn(mfn_to_shadow_page(sl1mfn)->v.sh.back);
     if ( mfn_valid(gl1mfn) 
          && mfn_is_out_of_sync(gl1mfn) )
     {
@@ -2968,7 +2968,7 @@ static int sh_page_fault(struct vcpu *v,
                                        sizeof(sl2e)) != 0)
                      || !(shadow_l2e_get_flags(sl2e) & _PAGE_PRESENT)
                      || !mfn_valid(gl1mfn = _mfn(mfn_to_shadow_page(
-                                      shadow_l2e_get_mfn(sl2e))->u.sh.back))
+                                      shadow_l2e_get_mfn(sl2e))->v.sh.back))
                      || unlikely(mfn_is_out_of_sync(gl1mfn)) )
                {
                    /* Hit the slow path as if there had been no 
@@ -3530,7 +3530,7 @@ sh_invlpg(struct vcpu *v, unsigned long va)
 #if (SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC) 
     /* Check to see if the SL1 is out of sync. */
     {
-        mfn_t gl1mfn = _mfn(mfn_to_shadow_page(sl1mfn)->u.sh.back);
+        mfn_t gl1mfn = _mfn(mfn_to_shadow_page(sl1mfn)->v.sh.back);
         struct page_info *pg = mfn_to_page(gl1mfn);
         if ( mfn_valid(gl1mfn) 
              && page_is_out_of_sync(pg) )
@@ -3560,7 +3560,7 @@ sh_invlpg(struct vcpu *v, unsigned long va)
             }
 
             sl1mfn = shadow_l2e_get_mfn(sl2e);
-            gl1mfn = _mfn(mfn_to_shadow_page(sl1mfn)->u.sh.back);
+            gl1mfn = _mfn(mfn_to_shadow_page(sl1mfn)->v.sh.back);
             pg = mfn_to_page(gl1mfn);
             
             if ( likely(sh_mfn_is_a_page_table(gl1mfn)
@@ -4887,7 +4887,7 @@ int sh_audit_l1_table(struct vcpu *v, mfn_t sl1mfn, mfn_t x)
     int done = 0;
     
     /* Follow the backpointer */
-    gl1mfn = _mfn(mfn_to_shadow_page(sl1mfn)->u.sh.back);
+    gl1mfn = _mfn(mfn_to_shadow_page(sl1mfn)->v.sh.back);
 
 #if (SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC)
     /* Out-of-sync l1 shadows can contain anything: just check the OOS hash */
@@ -4977,7 +4977,7 @@ int sh_audit_l2_table(struct vcpu *v, mfn_t sl2mfn, mfn_t x)
     int done = 0;
 
     /* Follow the backpointer */
-    gl2mfn = _mfn(mfn_to_shadow_page(sl2mfn)->u.sh.back);
+    gl2mfn = _mfn(mfn_to_shadow_page(sl2mfn)->v.sh.back);
 
 #if (SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC)
     /* Only L1's may be out of sync. */
@@ -5026,7 +5026,7 @@ int sh_audit_l3_table(struct vcpu *v, mfn_t sl3mfn, mfn_t x)
     int done = 0;
 
     /* Follow the backpointer */
-    gl3mfn = _mfn(mfn_to_shadow_page(sl3mfn)->u.sh.back);
+    gl3mfn = _mfn(mfn_to_shadow_page(sl3mfn)->v.sh.back);
 
 #if (SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC) 
     /* Only L1's may be out of sync. */
@@ -5073,7 +5073,7 @@ int sh_audit_l4_table(struct vcpu *v, mfn_t sl4mfn, mfn_t x)
     int done = 0;
 
     /* Follow the backpointer */
-    gl4mfn = _mfn(mfn_to_shadow_page(sl4mfn)->u.sh.back);
+    gl4mfn = _mfn(mfn_to_shadow_page(sl4mfn)->v.sh.back);
 
 #if (SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC) 
     /* Only L1's may be out of sync. */

xen/arch/x86/mm/shadow/private.h

@@ -631,7 +631,7 @@ static inline int sh_get_ref(struct vcpu *v, mfn_t smfn, paddr_t entry_pa)
     if ( unlikely(nx >= 1U<<26) )
     {
         SHADOW_PRINTK("shadow ref overflow, gmfn=%" PRpgmfn " smfn=%lx\n",
-                       sp->u.sh.back, mfn_x(smfn));
+                       sp->v.sh.back, mfn_x(smfn));
         return 0;
     }
     

xen/include/asm-x86/mm.h

@@ -15,7 +15,7 @@
  *  1. 'struct page_info' contains a 'struct page_list_entry list'.
  *  2. Provide a PFN_ORDER() macro for accessing the order of a free page.
  */
-#define PFN_ORDER(_pfn) ((_pfn)->u.free.order)
+#define PFN_ORDER(_pfn) ((_pfn)->v.free.order)
 
 /*
  * This definition is solely for the use in struct page_info (and
@@ -59,8 +59,6 @@ struct page_info
 
         /* Page is in use: ((count_info & PGC_count_mask) != 0). */
         struct {
-            /* Owner of this page (NULL if page is anonymous). */
-            u32 _domain; /* pickled format */
             /* Type reference count and various PGT_xxx flags and fields. */
             unsigned long type_info;
         } inuse;
@@ -70,24 +68,38 @@ struct page_info
             unsigned long type:5;   /* What kind of shadow is this? */
             unsigned long pinned:1; /* Is the shadow pinned? */
             unsigned long count:26; /* Reference count */
-            union {
-                /* When in use, GMFN of guest page we're a shadow of. */
-                __mfn_t back;
-                /* When free, order of the freelist we're on. */
-                unsigned int order;
-            };
         } sh;
 
         /* Page is on a free list: ((count_info & PGC_count_mask) == 0). */
         struct {
-            /* Order-size of the free chunk this page is the head of. */
-            u32 order;
             /* Mask of possibly-tainted TLBs. */
             cpumask_t cpumask;
         } free;
 
     } u;
 
+    union {
+
+        /* Page is in use, but not as a shadow. */
+        struct {
+            /* Owner of this page (NULL if page is anonymous). */
+            u32 _domain; /* pickled format */
+        } inuse;
+
+        /* Page is in use as a shadow. */
+        struct {
+            /* GMFN of guest page we're a shadow of. */
+            __mfn_t back;
+        } sh;
+
+        /* Page is on a free list (including shadow code free lists). */
+        struct {
+            /* Order-size of the free chunk this page is the head of. */
+            unsigned int order;
+        } free;
+
+    } v;
+
     union {
         /*
          * Timestamp from 'TLB clock', used to avoid extra safety flushes.
@@ -225,10 +237,10 @@ struct page_info
 #define SHADOW_OOS_FIXUPS 2
 
 #define page_get_owner(_p)                                              \
-    ((struct domain *)((_p)->u.inuse._domain ?                          \
-                       mfn_to_virt((_p)->u.inuse._domain) : NULL))
+    ((struct domain *)((_p)->v.inuse._domain ?                          \
+                       mfn_to_virt((_p)->v.inuse._domain) : NULL))
 #define page_set_owner(_p,_d)                                           \
-    ((_p)->u.inuse._domain = (_d) ? virt_to_mfn(_d) : 0)
+    ((_p)->v.inuse._domain = (_d) ? virt_to_mfn(_d) : 0)
 
 #define maddr_get_owner(ma)   (page_get_owner(maddr_to_page((ma))))
 #define vaddr_get_owner(va)   (page_get_owner(virt_to_page((va))))