tmem: Fix uses of unmatched __map_domain_page()

__map_domain_page() *must* be matched with an unmap_domain_page().  These five
static inline functions each map a page (or two), then throw away the context
needed to unmap it.

Each of the changes are limited to their respective functions.  In two cases,
this involved replacing a large amount of pointer arithmetic with memcpy()
(all callers were relying on memcpy() semantics of positive/negative returns
rather than specifically -1/+1). A third case had its pointer arithmetic
entirely replaced with memcpy().

In addition, remove redundant casts of void pointers and assertions.

This fixes Coverity IDs 1135373 1135374 1135375 1135376 1135377 1135378
11353739 which were retroactively identified following modelling improvements.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: Bob Liu <bob.liu@oracle.com>

xen/include/xen/tmem_xen.h

@@ -228,26 +228,24 @@ static inline bool_t tmem_current_is_privileged(void)
 
 static inline uint8_t tmem_get_first_byte(struct page_info *pfp)
 {
-    void *p = __map_domain_page(pfp);
+    const uint8_t *p = __map_domain_page(pfp);
+    uint8_t byte = p[0];
 
-    return (uint8_t)(*(char *)p);
+    unmap_domain_page(p);
+
+    return byte;
 }
 
 static inline int tmem_page_cmp(struct page_info *pfp1, struct page_info *pfp2)
 {
-    const uint64_t *p1 = (uint64_t *)__map_domain_page(pfp1);
-    const uint64_t *p2 = (uint64_t *)__map_domain_page(pfp2);
-    int i;
+    const uint64_t *p1 = __map_domain_page(pfp1);
+    const uint64_t *p2 = __map_domain_page(pfp2);
+    int rc = memcmp(p1, p2, PAGE_SIZE);
 
-    // FIXME: code in assembly?
-ASSERT(p1 != NULL);
-ASSERT(p2 != NULL);
-    for ( i = PAGE_SIZE/sizeof(uint64_t); i && *p1 == *p2; i--, p1++, p2++ );
-    if ( !i )
-        return 0;
-    if ( *p1 < *p2 )
-        return -1;
-    return 1;
+    unmap_domain_page(p2);
+    unmap_domain_page(p1);
+
+    return rc;
 }
 
 static inline int tmem_pcd_cmp(void *va1, pagesize_t len1, void *va2, pagesize_t len2)
@@ -271,54 +269,58 @@ static inline int tmem_pcd_cmp(void *va1, pagesize_t len1, void *va2, pagesize_t
     return 1;
 }
 
-static inline int tmem_tze_pfp_cmp(struct page_info *pfp1, pagesize_t pfp_len, void *tva, pagesize_t tze_len)
+static inline int tmem_tze_pfp_cmp(struct page_info *pfp1, pagesize_t pfp_len,
+                                   void *tva, const pagesize_t tze_len)
 {
-    const uint64_t *p1 = (uint64_t *)__map_domain_page(pfp1);
-    const uint64_t *p2;
-    pagesize_t i;
+    const uint64_t *p1 = __map_domain_page(pfp1);
+    const uint64_t *p2 = tze_len == PAGE_SIZE ?
+        __map_domain_page((struct page_info *)tva) : tva;
+    int rc;
 
-    if ( tze_len == PAGE_SIZE )
-       p2 = (uint64_t *)__map_domain_page((struct page_info *)tva);
-    else
-       p2 = (uint64_t *)tva;
     ASSERT(pfp_len <= PAGE_SIZE);
     ASSERT(!(pfp_len & (sizeof(uint64_t)-1)));
     ASSERT(tze_len <= PAGE_SIZE);
     ASSERT(!(tze_len & (sizeof(uint64_t)-1)));
     if ( pfp_len < tze_len )
-        return -1;
-    if ( pfp_len > tze_len )
-        return 1;
-    ASSERT(pfp_len == tze_len);
-    for ( i = tze_len/sizeof(uint64_t); i && *p1 == *p2; i--, p1++, p2++ );
-    if ( !i )
-        return 0;
-    if ( *p1 < *p2 )
-        return -1;
-    return 1;
+        rc = -1;
+    else if ( pfp_len > tze_len )
+        rc = 1;
+    else
+        rc = memcmp(p1, p2, tze_len);
+
+    if ( tze_len == PAGE_SIZE )
+        unmap_domain_page(p2);
+    unmap_domain_page(p1);
+
+    return rc;
 }
 
 /* return the size of the data in the pfp, ignoring trailing zeroes and
  * rounded up to the nearest multiple of 8 */
 static inline pagesize_t tmem_tze_pfp_scan(struct page_info *pfp)
 {
-    const uint64_t *p = (uint64_t *)__map_domain_page(pfp);
+    const uint64_t *const page = __map_domain_page(pfp);
+    const uint64_t *p = page;
     pagesize_t bytecount = PAGE_SIZE;
     pagesize_t len = PAGE_SIZE/sizeof(uint64_t);
+
     p += len;
     while ( len-- && !*--p )
         bytecount -= sizeof(uint64_t);
+
+    unmap_domain_page(page);
+
     return bytecount;
 }
 
 static inline void tmem_tze_copy_from_pfp(void *tva, struct page_info *pfp, pagesize_t len)
 {
-    uint64_t *p1 = (uint64_t *)tva;
-    const uint64_t *p2 = (uint64_t *)__map_domain_page(pfp);
+    const uint64_t *p = __map_domain_page(pfp);
 
-    pagesize_t i;
     ASSERT(!(len & (sizeof(uint64_t)-1)));
-    for ( i = len/sizeof(uint64_t); i--; *p1++ = *p2++);
+    memcpy(tva, p, len);
+
+    unmap_domain_page(p);
 }
 
 /* these typedefs are in the public/tmem.h interface