x86/mm: introduce l{1,2}t local variables to modify_xen_mappings

The pl2e and pl1e variables are heavily (ab)used in that function.  It
is fine at the moment because all page tables are always mapped so
there is no need to track the life time of each variable.

We will soon have the requirement to map and unmap page tables. We
need to track the life time of each variable to avoid leakage.

Introduce some l{1,2}t variables with limited scope so that we can
track life time of pointers to xen page tables more easily.

No functional change.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 5089fb10b910a61917c9dc451631cf958835109c..6b8eef36d6812d482112a04ed3f66a8fff5f6982 100644 (file)
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -5601,6 +5601,8 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
 
         if ( l3e_get_flags(*pl3e) & _PAGE_PSE )
         {
+            l2_pgentry_t *l2t;
+
             if ( l2_table_offset(v) == 0 &&
                  l1_table_offset(v) == 0 &&
                  ((e - v) >= (1UL << L3_PAGETABLE_SHIFT)) )
@@ -5616,11 +5618,11 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
             }
 
             /* PAGE1GB: shatter the superpage and fall through. */
-            pl2e = alloc_xen_pagetable();
-            if ( !pl2e )
+            l2t = alloc_xen_pagetable();
+            if ( !l2t )
                 return -ENOMEM;
             for ( i = 0; i < L2_PAGETABLE_ENTRIES; i++ )
-                l2e_write(pl2e + i,
+                l2e_write(l2t + i,
                           l2e_from_pfn(l3e_get_pfn(*pl3e) +
                                        (i << PAGETABLE_ORDER),
                                        l3e_get_flags(*pl3e)));
@@ -5629,14 +5631,14 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
             if ( (l3e_get_flags(*pl3e) & _PAGE_PRESENT) &&
                  (l3e_get_flags(*pl3e) & _PAGE_PSE) )
             {
-                l3e_write_atomic(pl3e, l3e_from_mfn(virt_to_mfn(pl2e),
+                l3e_write_atomic(pl3e, l3e_from_mfn(virt_to_mfn(l2t),
                                                     __PAGE_HYPERVISOR));
-                pl2e = NULL;
+                l2t = NULL;
             }
             if ( locking )
                 spin_unlock(&map_pgdir_lock);
-            if ( pl2e )
-                free_xen_pagetable(pl2e);
+            if ( l2t )
+                free_xen_pagetable(l2t);
         }
 
         /*
@@ -5670,12 +5672,14 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
             }
             else
             {
+                l1_pgentry_t *l1t;
+
                 /* PSE: shatter the superpage and try again. */
-                pl1e = alloc_xen_pagetable();
-                if ( !pl1e )
+                l1t = alloc_xen_pagetable();
+                if ( !l1t )
                     return -ENOMEM;
                 for ( i = 0; i < L1_PAGETABLE_ENTRIES; i++ )
-                    l1e_write(&pl1e[i],
+                    l1e_write(&l1t[i],
                               l1e_from_pfn(l2e_get_pfn(*pl2e) + i,
                                            l2e_get_flags(*pl2e) & ~_PAGE_PSE));
                 if ( locking )
@@ -5683,19 +5687,19 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
                 if ( (l2e_get_flags(*pl2e) & _PAGE_PRESENT) &&
                      (l2e_get_flags(*pl2e) & _PAGE_PSE) )
                 {
-                    l2e_write_atomic(pl2e, l2e_from_mfn(virt_to_mfn(pl1e),
+                    l2e_write_atomic(pl2e, l2e_from_mfn(virt_to_mfn(l1t),
                                                         __PAGE_HYPERVISOR));
-                    pl1e = NULL;
+                    l1t = NULL;
                 }
                 if ( locking )
                     spin_unlock(&map_pgdir_lock);
-                if ( pl1e )
-                    free_xen_pagetable(pl1e);
+                if ( l1t )
+                    free_xen_pagetable(l1t);
             }
         }
         else
         {
-            l1_pgentry_t nl1e;
+            l1_pgentry_t nl1e, *l1t;
 
             /*
              * Ordinary 4kB mapping: The L2 entry has been verified to be
@@ -5742,9 +5746,9 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
                 continue;
             }
 
-            pl1e = l2e_to_l1e(*pl2e);
+            l1t = l2e_to_l1e(*pl2e);
             for ( i = 0; i < L1_PAGETABLE_ENTRIES; i++ )
-                if ( l1e_get_intpte(pl1e[i]) != 0 )
+                if ( l1e_get_intpte(l1t[i]) != 0 )
                     break;
             if ( i == L1_PAGETABLE_ENTRIES )
             {
@@ -5753,7 +5757,7 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
                 if ( locking )
                     spin_unlock(&map_pgdir_lock);
                 flush_area(NULL, FLUSH_TLB_GLOBAL); /* flush before free */
-                free_xen_pagetable(pl1e);
+                free_xen_pagetable(l1t);
             }
             else if ( locking )
                 spin_unlock(&map_pgdir_lock);
@@ -5782,21 +5786,25 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
             continue;
         }
 
-        pl2e = l3e_to_l2e(*pl3e);
-        for ( i = 0; i < L2_PAGETABLE_ENTRIES; i++ )
-            if ( l2e_get_intpte(pl2e[i]) != 0 )
-                break;
-        if ( i == L2_PAGETABLE_ENTRIES )
         {
-            /* Empty: zap the L3E and free the L2 page. */
-            l3e_write_atomic(pl3e, l3e_empty());
-            if ( locking )
+            l2_pgentry_t *l2t;
+
+            l2t = l3e_to_l2e(*pl3e);
+            for ( i = 0; i < L2_PAGETABLE_ENTRIES; i++ )
+                if ( l2e_get_intpte(l2t[i]) != 0 )
+                    break;
+            if ( i == L2_PAGETABLE_ENTRIES )
+            {
+                /* Empty: zap the L3E and free the L2 page. */
+                l3e_write_atomic(pl3e, l3e_empty());
+                if ( locking )
+                    spin_unlock(&map_pgdir_lock);
+                flush_area(NULL, FLUSH_TLB_GLOBAL); /* flush before free */
+                free_xen_pagetable(l2t);
+            }
+            else if ( locking )
                 spin_unlock(&map_pgdir_lock);
-            flush_area(NULL, FLUSH_TLB_GLOBAL); /* flush before free */
-            free_xen_pagetable(pl2e);
         }
-        else if ( locking )
-            spin_unlock(&map_pgdir_lock);
     }
 
     flush_area(NULL, FLUSH_TLB_GLOBAL);