tcg: remove tb_lock

Use mmap_lock in user-mode to protect TCG state and the page descriptors.
In !user-mode, each vCPU has its own TCG state, so no locks needed.
Per-page locks are used to protect the page descriptors.

Per-TB locks are used in both modes to protect TB jumps.

Some notes:

- tb_lock is removed from notdirty_mem_write by passing a
  locked page_collection to tb_invalidate_phys_page_fast.

- tcg_tb_lookup/remove/insert/etc have their own internal lock(s),
  so there is no need to further serialize access to them.

- do_tb_flush is run in a safe async context, meaning no other
  vCPU threads are running. Therefore acquiring mmap_lock there
  is just to please tools such as thread sanitizer.

- Not visible in the diff, but tb_invalidate_phys_page already
  has an assert_memory_lock.

- cpu_io_recompile is !user-only, so no mmap_lock there.

- Added mmap_unlock()'s before all siglongjmp's that could
  be called in user-mode while mmap_lock is held.
  + Added an assert for !have_mmap_lock() after returning from
    the longjmp in cpu_exec, just like we do in cpu_exec_step_atomic.

Performance numbers before/after:

Host: AMD Opteron(tm) Processor 6376

                 ubuntu 17.04 ppc64 bootup+shutdown time

  700 +-+--+----+------+------------+-----------+------------*--+-+
      |    +    +      +            +           +           *B    |
      |         before ***B***                            ** *    |
      |tb lock removal ###D###                         ***        |
  600 +-+                                           ***         +-+
      |                                           **         #    |
      |                                        *B*          #D    |
      |                                     *** *         ##      |
  500 +-+                                ***           ###      +-+
      |                             * ***           ###           |
      |                            *B*          # ##              |
      |                          ** *          #D#                |
  400 +-+                      **            ##                 +-+
      |                      **           ###                     |
      |                    **           ##                        |
      |                  **         # ##                          |
  300 +-+  *           B*          #D#                          +-+
      |    B         ***        ###                               |
      |    *       **       ####                                  |
      |     *   ***      ###                                      |
  200 +-+   B  *B     #D#                                       +-+
      |     #B* *   ## #                                          |
      |     #*    ##                                              |
      |    + D##D#     +            +           +            +    |
  100 +-+--+----+------+------------+-----------+------------+--+-+
           1    8      16      Guest CPUs       48           64
  png: https://imgur.com/HwmBHXe

              debian jessie aarch64 bootup+shutdown time

  90 +-+--+-----+-----+------------+------------+------------+--+-+
     |    +     +     +            +            +            +    |
     |         before ***B***                                B    |
  80 +tb lock removal ###D###                              **D  +-+
     |                                                   **###    |
     |                                                 **##       |
  70 +-+                                             ** #       +-+
     |                                             ** ##          |
     |                                           **  #            |
  60 +-+                                       *B  ##           +-+
     |                                       **  ##               |
     |                                    ***  #D                 |
  50 +-+                               ***   ##                 +-+
     |                             * **   ###                     |
     |                           **B*  ###                        |
  40 +-+                     ****  # ##                         +-+
     |                   ****     #D#                             |
     |             ***B**      ###                                |
  30 +-+    B***B**        ####                                 +-+
     |    B *   *     # ###                                       |
     |     B       ###D#                                          |
  20 +-+   D  ##D##                                             +-+
     |      D#                                                    |
     |    +     +     +            +            +            +    |
  10 +-+--+-----+-----+------------+------------+------------+--+-+
          1     8     16      Guest CPUs        48           64
  png: https://imgur.com/iGpGFtv

The gains are high for 4-8 CPUs. Beyond that point, however, unrelated
lock contention significantly hurts scalability.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/exec/memory-internal.h

@@ -49,6 +49,8 @@ void mtree_print_dispatch(fprintf_function mon, void *f,
                           struct AddressSpaceDispatch *d,
                           MemoryRegion *root);
 
+struct page_collection;
+
 /* Opaque struct for passing info from memory_notdirty_write_prepare()
  * to memory_notdirty_write_complete(). Callers should treat all fields
  * as private, with the exception of @active.
@@ -60,10 +62,10 @@ void mtree_print_dispatch(fprintf_function mon, void *f,
  */
 typedef struct {
     CPUState *cpu;
+    struct page_collection *pages;
     ram_addr_t ram_addr;
     vaddr mem_vaddr;
     unsigned size;
-    bool locked;
     bool active;
 } NotDirtyInfo;
 
@@ -91,7 +93,7 @@ typedef struct {
  *
  * This must only be called if we are using TCG; it will assert otherwise.
  *
- * We may take a lock in the prepare call, so callers must ensure that
+ * We may take locks in the prepare call, so callers must ensure that
  * they don't exit (via longjump or otherwise) without calling complete.
  *
  * This call must only be made inside an RCU critical section.