tcg: Prepare TB invalidation for lockless TB lookup

When invalidating a translation block, set an invalid flag into the
TranslationBlock structure first.  It is also necessary to check whether
the target TB is still valid after acquiring 'tb_lock' but before calling
tb_add_jump() since TB lookup is to be performed out of 'tb_lock' in
future. Note that we don't have to check 'last_tb'; an already invalidated
TB will not be executed anyway and it is thus safe to patch it.
Suggested-by: NSergey Fedorov <serge.fdrv@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

cpu-exec.c

@@ -241,7 +241,8 @@ static bool tb_cmp(const void *p, const void *d)
     if (tb->pc == desc->pc &&
         tb->page_addr[0] == desc->phys_page1 &&
         tb->cs_base == desc->cs_base &&
-        tb->flags == desc->flags) {
+        tb->flags == desc->flags &&
+        !atomic_read(&tb->invalid)) {
         /* check next page if needed */
         if (tb->page_addr[1] == -1) {
             return true;
@@ -352,7 +353,7 @@ static inline TranslationBlock *tb_find_fast(CPUState *cpu,
         /* Check if translation buffer has been flushed */
         if (cpu->tb_flushed) {
             cpu->tb_flushed = false;
-        } else {
+        } else if (!tb->invalid) {
             tb_add_jump(last_tb, tb_exit, tb);
         }
     }

include/exec/exec-all.h

@@ -225,6 +225,8 @@ struct TranslationBlock {
 #define CF_USE_ICOUNT  0x20000
 #define CF_IGNORE_ICOUNT 0x40000 /* Do not generate icount code */
 
+    uint16_t invalid;
+
     void *tc_ptr;    /* pointer to the translated code */
     uint8_t *tc_search;  /* pointer to search data */
     /* original tb when cflags has CF_NOCACHE */

translate-all.c

@@ -773,6 +773,7 @@ static TranslationBlock *tb_alloc(target_ulong pc)
     tb = &tcg_ctx.tb_ctx.tbs[tcg_ctx.tb_ctx.nb_tbs++];
     tb->pc = pc;
     tb->cflags = 0;
+    tb->invalid = false;
     return tb;
 }
 
@@ -994,6 +995,8 @@ void tb_phys_invalidate(TranslationBlock *tb, tb_page_addr_t page_addr)
     uint32_t h;
     tb_page_addr_t phys_pc;
 
+    atomic_set(&tb->invalid, true);
+
     /* remove the TB from the hash list */
     phys_pc = tb->page_addr[0] + (tb->pc & ~TARGET_PAGE_MASK);
     h = tb_hash_func(phys_pc, tb->pc, tb->flags);