virtio-balloon: Better names for offset variables in inflate/deflate …

…code

"host_page_base" is really confusing, let's make this clearer, also
rename the other offsets to indicate to which base they apply.

offset -> mr_offset
ram_offset -> rb_offset
host_page_base -> rb_aligned_offset

While at it, use QEMU_ALIGN_DOWN() instead of a handcrafted computation
and move the computation to the place where it is needed.

Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20190722134108.22151-5-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit e6129b2)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

hw/virtio/virtio-balloon.c

@@ -40,24 +40,23 @@ struct PartiallyBalloonedPage {
 };
 
 static void balloon_inflate_page(VirtIOBalloon *balloon,
-                                 MemoryRegion *mr, hwaddr offset)
+                                 MemoryRegion *mr, hwaddr mr_offset)
 {
-    void *addr = memory_region_get_ram_ptr(mr) + offset;
+    void *addr = memory_region_get_ram_ptr(mr) + mr_offset;
+    ram_addr_t rb_offset, rb_aligned_offset;
     RAMBlock *rb;
     size_t rb_page_size;
     int subpages;
-    ram_addr_t ram_offset, host_page_base;
 
     /* XXX is there a better way to get to the RAMBlock than via a
      * host address? */
-    rb = qemu_ram_block_from_host(addr, false, &ram_offset);
+    rb = qemu_ram_block_from_host(addr, false, &rb_offset);
     rb_page_size = qemu_ram_pagesize(rb);
-    host_page_base = ram_offset & ~(rb_page_size - 1);
 
     if (rb_page_size == BALLOON_PAGE_SIZE) {
         /* Easy case */
 
-        ram_block_discard_range(rb, ram_offset, rb_page_size);
+        ram_block_discard_range(rb, rb_offset, rb_page_size);
         /* We ignore errors from ram_block_discard_range(), because it
          * has already reported them, and failing to discard a balloon
          * page is not fatal */
@@ -73,11 +72,12 @@ static void balloon_inflate_page(VirtIOBalloon *balloon,
     warn_report_once(
 "Balloon used with backing page size > 4kiB, this may not be reliable");
 
+    rb_aligned_offset = QEMU_ALIGN_DOWN(rb_offset, rb_page_size);
     subpages = rb_page_size / BALLOON_PAGE_SIZE;
 
     if (balloon->pbp
         && (rb != balloon->pbp->rb
-            || host_page_base != balloon->pbp->base)) {
+            || rb_aligned_offset != balloon->pbp->base)) {
         /* We've partially ballooned part of a host page, but now
          * we're trying to balloon part of a different one.  Too hard,
          * give up on the old partial page */
@@ -90,10 +90,10 @@ static void balloon_inflate_page(VirtIOBalloon *balloon,
         size_t bitlen = BITS_TO_LONGS(subpages) * sizeof(unsigned long);
         balloon->pbp = g_malloc0(sizeof(PartiallyBalloonedPage) + bitlen);
         balloon->pbp->rb = rb;
-        balloon->pbp->base = host_page_base;
+        balloon->pbp->base = rb_aligned_offset;
     }
 
-    set_bit((ram_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE,
+    set_bit((rb_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE,
             balloon->pbp->bitmap);
 
     if (bitmap_full(balloon->pbp->bitmap, subpages)) {
@@ -111,18 +111,18 @@ static void balloon_inflate_page(VirtIOBalloon *balloon,
 }
 
 static void balloon_deflate_page(VirtIOBalloon *balloon,
-                                 MemoryRegion *mr, hwaddr offset)
+                                 MemoryRegion *mr, hwaddr mr_offset)
 {
-    void *addr = memory_region_get_ram_ptr(mr) + offset;
+    void *addr = memory_region_get_ram_ptr(mr) + mr_offset;
+    ram_addr_t rb_offset;
     RAMBlock *rb;
     size_t rb_page_size;
-    ram_addr_t ram_offset;
     void *host_addr;
     int ret;
 
     /* XXX is there a better way to get to the RAMBlock than via a
      * host address? */
-    rb = qemu_ram_block_from_host(addr, false, &ram_offset);
+    rb = qemu_ram_block_from_host(addr, false, &rb_offset);
     rb_page_size = qemu_ram_pagesize(rb);
 
     if (balloon->pbp) {