[Qemu-devel] [PATCH] accel/tcg: Consider cluster index in tb_lookup__cpu_state()

[Peter Maydell]

In commit f7b78602fdc6c6e4be we added the CPU cluster number to the
cflags field of the TB hash; this included adding it to the value
kept in tb->cflags, since we pass that field directly into the hash
calculation in some places. Unfortunately we forgot to check whether
other parts of the code were doing comparisons against tb->cflags
that would need to be updated.

It turns out that there is exactly one such place: the
tb_lookup__cpu_state() function checks whether the TB it has
found in the tb_jmp_cache has a tb->cflags matching the cf_mask
that is passed in. The tb->cflags has the cluster_index in it
but the cf_mask does not.

Hoist the "add cluster index to the cf_mask" code up from
tb_htable_lookup() to tb_lookup__cpu_state() so it can be considered
in the "did this TB match in the jmp cache" condition, as well as
when we do the full hash lookup by physical PC, flags, etc.
(tb_htable_lookup() is only called from tb_lookup__cpu_state(),
so this change doesn't require any further knock-on changes.)

Fixes: f7b78602fdc6c6e4be ("accel/tcg: Add cluster number to TCG TB hash")
Reported-by: Howard Spoelstra <address@hidden>
Reported-by: Cleber Rosa <address@hidden>
Signed-off-by: Peter Maydell <address@hidden>
---
Does anybody know why tb_lookup__cpu_state() has that odd
double-underscore in the middle of its name?

Since the jmp_cache is per-vcpu we know that we're always going
to match on the cluster_index, so the other option would be to
leave the cluster_index bits out of the comparison, and leave the
"fold in cluster index to cf_mask" code in tb_htable_lookup().
Or we could require the callers of tb_lookup__cpu_state() to all
provide the cluster index, but that's more places to change,
so I prefer this.
---
 include/exec/tb-lookup.h | 4 ++++
 accel/tcg/cpu-exec.c     | 3 ---
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/exec/tb-lookup.h b/include/exec/tb-lookup.h
index 492cb682894..26921b6dafd 100644
--- a/include/exec/tb-lookup.h
+++ b/include/exec/tb-lookup.h
@@ -28,6 +28,10 @@ tb_lookup__cpu_state(CPUState *cpu, target_ulong *pc, 
target_ulong *cs_base,
     cpu_get_tb_cpu_state(env, pc, cs_base, flags);
     hash = tb_jmp_cache_hash_func(*pc);
     tb = atomic_rcu_read(&cpu->tb_jmp_cache[hash]);
+
+    cf_mask &= ~CF_CLUSTER_MASK;
+    cf_mask |= cpu->cluster_index << CF_CLUSTER_SHIFT;
+
     if (likely(tb &&
                tb->pc == *pc &&
                tb->cs_base == *cs_base &&
diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
index 7cf1292546f..60d87d5a19b 100644
--- a/accel/tcg/cpu-exec.c
+++ b/accel/tcg/cpu-exec.c
@@ -325,9 +325,6 @@ TranslationBlock *tb_htable_lookup(CPUState *cpu, 
target_ulong pc,
     struct tb_desc desc;
     uint32_t h;
 
-    cf_mask &= ~CF_CLUSTER_MASK;
-    cf_mask |= cpu->cluster_index << CF_CLUSTER_SHIFT;
-
     desc.env = (CPUArchState *)cpu->env_ptr;
     desc.cs_base = cs_base;
     desc.flags = flags;
-- 
2.20.1