[Qemu-devel] [PATCH v3 07/11] tcg: Prepare TB invalidation for lockless TB lookup

[Sergey Fedorov]

From: Sergey Fedorov <address@hidden>

When invalidating a translation block, set an invalid CPU state into the
TranslationBlock structure first. All subsequent changes are ordered
after it with smp_wmb(). This pairs with implied smp_rmb() of
qht_lookup() in tb_find_physical().

As soon as the TB is marked with an invalid CPU state, there is no need
to remove it from CPU's 'tb_jmp_cache'. However it will be necessary to
recheck 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' since
it is safe to patch an already invalidated TB since it will not be
executed anyway.

Suggested-by: Paolo Bonzini <address@hidden>
Signed-off-by: Sergey Fedorov <address@hidden>
Signed-off-by: Sergey Fedorov <address@hidden>
---
 cpu-exec.c      |  2 +-
 translate-all.c | 12 +++---------
 2 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/cpu-exec.c b/cpu-exec.c
index c973e3b85922..07dc50c56e8d 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -352,7 +352,7 @@ 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_is_invalid(tb)) {
             tb_add_jump(last_tb, tb_exit, tb);
         }
     }
diff --git a/translate-all.c b/translate-all.c
index 788fed1e0765..ee8308209350 100644
--- a/translate-all.c
+++ b/translate-all.c
@@ -986,11 +986,13 @@ static inline void tb_jmp_unlink(TranslationBlock *tb)
 /* invalidate one TB */
 void tb_phys_invalidate(TranslationBlock *tb, tb_page_addr_t page_addr)
 {
-    CPUState *cpu;
     PageDesc *p;
     uint32_t h;
     tb_page_addr_t phys_pc;
 
+    tb_mark_invalid(tb);
+    smp_wmb();
+
     /* 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);
@@ -1008,14 +1010,6 @@ void tb_phys_invalidate(TranslationBlock *tb, 
tb_page_addr_t page_addr)
         invalidate_page_bitmap(p);
     }
 
-    /* remove the TB from the hash list */
-    h = tb_jmp_cache_hash_func(tb->pc);
-    CPU_FOREACH(cpu) {
-        if (atomic_read(&cpu->tb_jmp_cache[h]) == tb) {
-            atomic_set(&cpu->tb_jmp_cache[h], NULL);
-        }
-    }
-
     /* suppress this TB from the two jump lists */
     tb_remove_from_jmp_list(tb, 0);
     tb_remove_from_jmp_list(tb, 1);
-- 
1.9.1