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Re: [Qemu-devel] [PATCH v3 07/11] tcg: Prepare TB invalidation for lockl
From: |
Alex Bennée |
Subject: |
Re: [Qemu-devel] [PATCH v3 07/11] tcg: Prepare TB invalidation for lockless TB lookup |
Date: |
Thu, 14 Jul 2016 13:59:20 +0100 |
User-agent: |
mu4e 0.9.17; emacs 25.0.95.9 |
Sergey Fedorov <address@hidden> writes:
> 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.
This looks fine. So I guess it's possible for the block to have been
looked up just before it gets invalidated and get one final run but not
get patched?
Reviewed-by: Alex Bennée <address@hidden>
>
> 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);
--
Alex Bennée
- Re: [Qemu-devel] [PATCH v3 03/11] tcg: Prepare safe tb_jmp_cache lookup out of tb_lock, (continued)
- [Qemu-devel] [PATCH v3 05/11] target-i386: Remove redundant HF_SOFTMMU_MASK, Sergey Fedorov, 2016/07/12
- [Qemu-devel] [PATCH v3 08/11] tcg: set up tb->page_addr before insertion, Sergey Fedorov, 2016/07/12
- [Qemu-devel] [PATCH v3 07/11] tcg: Prepare TB invalidation for lockless TB lookup, Sergey Fedorov, 2016/07/12
- Re: [Qemu-devel] [PATCH v3 07/11] tcg: Prepare TB invalidation for lockless TB lookup,
Alex Bennée <=
- [Qemu-devel] [PATCH v3 09/11] tcg: cpu-exec: remove tb_lock from the hot-path, Sergey Fedorov, 2016/07/12
- [Qemu-devel] [PATCH v3 06/11] tcg: Introduce tb_mark_invalid() and tb_is_invalid(), Sergey Fedorov, 2016/07/12
Re: [Qemu-devel] [PATCH v3 06/11] tcg: Introduce tb_mark_invalid() and tb_is_invalid(), Alex Bennée, 2016/07/14