From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47419) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bNgQJ-0002HM-Vx for qemu-devel@nongnu.org; Thu, 14 Jul 2016 09:11:29 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bNgQE-0002XP-UP for qemu-devel@nongnu.org; Thu, 14 Jul 2016 09:11:26 -0400 Received: from mail-lf0-x242.google.com ([2a00:1450:4010:c07::242]:35639) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bNgQE-0002XF-IU for qemu-devel@nongnu.org; Thu, 14 Jul 2016 09:11:22 -0400 Received: by mail-lf0-x242.google.com with SMTP id l89so5366954lfi.2 for ; Thu, 14 Jul 2016 06:11:22 -0700 (PDT) References: <1468354426-837-1-git-send-email-sergey.fedorov@linaro.org> <1468354426-837-8-git-send-email-sergey.fedorov@linaro.org> <87mvlk4bpz.fsf@linaro.org> From: Sergey Fedorov Message-ID: <57878F78.1080000@gmail.com> Date: Thu, 14 Jul 2016 16:11:20 +0300 MIME-Version: 1.0 In-Reply-To: <87mvlk4bpz.fsf@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH v3 07/11] tcg: Prepare TB invalidation for lockless TB lookup List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?UTF-8?Q?Alex_Benn=c3=a9e?= , Sergey Fedorov Cc: qemu-devel@nongnu.org, mttcg@listserver.greensocs.com, fred.konrad@greensocs.com, a.rigo@virtualopensystems.com, cota@braap.org, bobby.prani@gmail.com, rth@twiddle.net, patches@linaro.org, mark.burton@greensocs.com, pbonzini@redhat.com, jan.kiszka@siemens.com, peter.maydell@linaro.org, claudio.fontana@huawei.com, Peter Crosthwaite On 14/07/16 15:59, Alex Bennée wrote: > Sergey Fedorov writes: > >> From: Sergey Fedorov >> >> 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? Yes, exactly. Thanks, Sergey > > Reviewed-by: Alex Bennée > >> Suggested-by: Paolo Bonzini >> Signed-off-by: Sergey Fedorov >> Signed-off-by: Sergey Fedorov >> --- >> 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