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[Qemu-devel] [PATCH 04/10] tcg: Prepare safe access to tb_flushed out of
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH 04/10] tcg: Prepare safe access to tb_flushed out of tb_lock |
Date: |
Tue, 19 Jul 2016 10:32:15 +0200 |
From: Sergey Fedorov <address@hidden>
Ensure atomicity and ordering of CPU's 'tb_flushed' access for future
translation block lookup out of 'tb_lock'.
This field can only be touched from another thread by tb_flush() in user
mode emulation. So the only access to be sequential atomic is:
* a single write in tb_flush();
* reads/writes out of 'tb_lock'.
In future, before enabling MTTCG in system mode, tb_flush() must be safe
and this field becomes unnecessary.
Signed-off-by: Sergey Fedorov <address@hidden>
Signed-off-by: Sergey Fedorov <address@hidden>
Reviewed-by: Alex Bennée <address@hidden>
Message-Id: <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
---
cpu-exec.c | 16 +++++++---------
translate-all.c | 4 ++--
2 files changed, 9 insertions(+), 11 deletions(-)
diff --git a/cpu-exec.c b/cpu-exec.c
index 32b58ed..877ff8e 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -338,13 +338,6 @@ static inline TranslationBlock *tb_find_fast(CPUState *cpu,
tb->flags != flags)) {
tb = tb_find_slow(cpu, pc, cs_base, flags);
}
- if (cpu->tb_flushed) {
- /* Ensure that no TB jump will be modified as the
- * translation buffer has been flushed.
- */
- last_tb = NULL;
- cpu->tb_flushed = false;
- }
#ifndef CONFIG_USER_ONLY
/* We don't take care of direct jumps when address mapping changes in
* system emulation. So it's not safe to make a direct jump to a TB
@@ -356,7 +349,12 @@ static inline TranslationBlock *tb_find_fast(CPUState *cpu,
#endif
/* See if we can patch the calling TB. */
if (last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
- tb_add_jump(last_tb, tb_exit, tb);
+ /* Check if translation buffer has been flushed */
+ if (cpu->tb_flushed) {
+ cpu->tb_flushed = false;
+ } else {
+ tb_add_jump(last_tb, tb_exit, tb);
+ }
}
tb_unlock();
return tb;
@@ -617,7 +615,7 @@ int cpu_exec(CPUState *cpu)
break;
}
- cpu->tb_flushed = false; /* reset before first TB lookup */
+ atomic_mb_set(&cpu->tb_flushed, false); /* reset before first TB
lookup */
for(;;) {
cpu_handle_interrupt(cpu, &last_tb);
tb = tb_find_fast(cpu, last_tb, tb_exit);
diff --git a/translate-all.c b/translate-all.c
index fdf520a..788fed1 100644
--- a/translate-all.c
+++ b/translate-all.c
@@ -845,7 +845,6 @@ void tb_flush(CPUState *cpu)
> tcg_ctx.code_gen_buffer_size) {
cpu_abort(cpu, "Internal error: code buffer overflow\n");
}
- tcg_ctx.tb_ctx.nb_tbs = 0;
CPU_FOREACH(cpu) {
int i;
@@ -853,9 +852,10 @@ void tb_flush(CPUState *cpu)
for (i = 0; i < TB_JMP_CACHE_SIZE; ++i) {
atomic_set(&cpu->tb_jmp_cache[i], NULL);
}
- cpu->tb_flushed = true;
+ atomic_mb_set(&cpu->tb_flushed, true);
}
+ tcg_ctx.tb_ctx.nb_tbs = 0;
qht_reset_size(&tcg_ctx.tb_ctx.htable, CODE_GEN_HTABLE_SIZE);
page_flush_tb();
--
2.7.4
- [Qemu-devel] [PATCH v5 00/10] Reduce lock contention on TCG hot-path, Paolo Bonzini, 2016/07/19
- [Qemu-devel] [PATCH 02/10] tcg: Pass last_tb by value to tb_find_fast(), Paolo Bonzini, 2016/07/19
- [Qemu-devel] [PATCH 01/10] util/qht: Document memory ordering assumptions, Paolo Bonzini, 2016/07/19
- [Qemu-devel] [PATCH 05/10] tcg: Prepare TB invalidation for lockless TB lookup, Paolo Bonzini, 2016/07/19
- [Qemu-devel] [PATCH 03/10] tcg: Prepare safe tb_jmp_cache lookup out of tb_lock, Paolo Bonzini, 2016/07/19
- [Qemu-devel] [PATCH 04/10] tcg: Prepare safe access to tb_flushed out of tb_lock,
Paolo Bonzini <=
- [Qemu-devel] [PATCH 06/10] tcg: set up tb->page_addr before insertion, Paolo Bonzini, 2016/07/19
- [Qemu-devel] [PATCH 08/10] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Paolo Bonzini, 2016/07/19
- [Qemu-devel] [PATCH 10/10] tcg: rename tb_find_physical(), Paolo Bonzini, 2016/07/19
- [Qemu-devel] [PATCH 09/10] tcg: Merge tb_find_slow() and tb_find_fast(), Paolo Bonzini, 2016/07/19
- [Qemu-devel] [PATCH 07/10] tcg: cpu-exec: remove tb_lock from the hot-path, Paolo Bonzini, 2016/07/19