From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46776) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b0TW0-0000t1-53 for qemu-devel@nongnu.org; Wed, 11 May 2016 08:45:25 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b0TVu-0007Zk-Sj for qemu-devel@nongnu.org; Wed, 11 May 2016 08:45:23 -0400 Received: from mail-lf0-x241.google.com ([2a00:1450:4010:c07::241]:34401) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b0TVu-0007Ze-Fu for qemu-devel@nongnu.org; Wed, 11 May 2016 08:45:18 -0400 Received: by mail-lf0-x241.google.com with SMTP id m101so4990907lfi.1 for ; Wed, 11 May 2016 05:45:17 -0700 (PDT) References: <1459870344-16773-1-git-send-email-alex.bennee@linaro.org> <1459870344-16773-6-git-send-email-alex.bennee@linaro.org> From: Sergey Fedorov Message-ID: <5733295B.8090401@gmail.com> Date: Wed, 11 May 2016 15:45:15 +0300 MIME-Version: 1.0 In-Reply-To: <1459870344-16773-6-git-send-email-alex.bennee@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [RFC v2 05/11] tcg: protect TBContext with tb_lock. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?UTF-8?Q?Alex_Benn=c3=a9e?= , mttcg@listserver.greensocs.com, fred.konrad@greensocs.com, a.rigo@virtualopensystems.com, cota@braap.org Cc: qemu-devel@nongnu.org, mark.burton@greensocs.com, pbonzini@redhat.com, jan.kiszka@siemens.com, rth@twiddle.net, peter.maydell@linaro.org, claudio.fontana@huawei.com, Peter Crosthwaite , "Michael S. Tsirkin" , Eduardo Habkost On 05/04/16 18:32, Alex Bennée wrote: (snip) > diff --git a/cpu-exec.c b/cpu-exec.c > index 74065d9..bd50fef 100644 > --- a/cpu-exec.c > +++ b/cpu-exec.c > @@ -205,18 +205,24 @@ static void cpu_exec_nocache(CPUState *cpu, int max_cycles, > if (max_cycles > CF_COUNT_MASK) > max_cycles = CF_COUNT_MASK; > > + tb_lock(); > cpu->tb_invalidated_flag = false; > tb = tb_gen_code(cpu, orig_tb->pc, orig_tb->cs_base, orig_tb->flags, > max_cycles | CF_NOCACHE > | (ignore_icount ? CF_IGNORE_ICOUNT : 0)); > tb->orig_tb = cpu->tb_invalidated_flag ? NULL : orig_tb; > cpu->current_tb = tb; > + tb_unlock(); > + > /* execute the generated code */ > trace_exec_tb_nocache(tb, tb->pc); > - cpu_tb_exec(cpu, tb); > + cpu_tb_exec(cpu, tb->tc_ptr); Very suspicious change. I can't even find which patch changes cpu_tb_exec() accordingly. > + > + tb_lock(); > cpu->current_tb = NULL; > tb_phys_invalidate(tb, -1); > tb_free(tb); > + tb_unlock(); > } > #endif > > diff --git a/exec.c b/exec.c > index 17f390e..c46c123 100644 > --- a/exec.c > +++ b/exec.c > @@ -2111,6 +2111,9 @@ static void check_watchpoint(int offset, int len, MemTxAttrs attrs, int flags) > continue; > } > cpu->watchpoint_hit = wp; > + > + /* Unlocked by cpu_loop_exit or cpu_resume_from_signal. */ In fact, neither cpu_resume_from_signal() nor cpu_loop_exit() unlocks the lock by itself, it gets unlocked after sigsetjmp() returns via siglongjmp() back to cpu_exec(). So maybe it would be more clear to say something like "'tb_lock' gets unlocked after siglongjmp()"? > + tb_lock(); > tb_check_watchpoint(cpu); > if (wp->flags & BP_STOP_BEFORE_ACCESS) { > cpu->exception_index = EXCP_DEBUG; (snip) > diff --git a/translate-all.c b/translate-all.c > index a7ff5e7..935d24c 100644 > --- a/translate-all.c > +++ b/translate-all.c > @@ -834,7 +834,9 @@ static void page_flush_tb(void) > } > > /* flush all the translation blocks */ > -/* XXX: tb_flush is currently not thread safe */ > +/* XXX: tb_flush is currently not thread safe. System emulation calls it only > + * with tb_lock taken or from safe_work, so no need to take tb_lock here. > + */ "System emulation"? What about user-mode emulation? > void tb_flush(CPUState *cpu) > { > #if defined(DEBUG_FLUSH) > @@ -1350,6 +1352,7 @@ void tb_invalidate_phys_page_range(tb_page_addr_t start, tb_page_addr_t end, > /* we remove all the TBs in the range [start, end[ */ > /* XXX: see if in some cases it could be faster to invalidate all > the code */ > + tb_lock(); Don't we need also protect a call to page_find() above? page_find() calls page_find_alloc() which is noted to be called with 'tb_lock' held. However, it might depend on the way we treat 'mmap_lock' in system mode emulation. We might also consider taking the lock outside of tb_invalidate_phys*() functions because they can be called after page_find(). > tb = p->first_tb; > while (tb != NULL) { > n = (uintptr_t)tb & 3; > @@ -1417,12 +1420,13 @@ void tb_invalidate_phys_page_range(tb_page_addr_t start, tb_page_addr_t end, > if (current_tb_modified) { > /* we generate a block containing just the instruction > modifying the memory. It will ensure that it cannot modify > - itself */ > + itself. cpu_resume_from_signal unlocks tb_lock. */ > cpu->current_tb = NULL; > tb_gen_code(cpu, current_pc, current_cs_base, current_flags, 1); > cpu_resume_from_signal(cpu, NULL); > } > #endif > + tb_unlock(); > } > > #ifdef CONFIG_SOFTMMU (snip) > @ -1627,6 +1636,7 @@ void cpu_io_recompile(CPUState *cpu, uintptr_t retaddr) > target_ulong pc, cs_base; > uint64_t flags; > > + tb_lock(); We don't have to take 'tb_lock' for nether tb_find_pc() nor cpu_restore_state_from_tb() because the lock does not protect from tb_flush() anyway. I think the lock should be taken just before the first call to tb_phys_invalidate() in this function. > tb = tb_find_pc(retaddr); > if (!tb) { > cpu_abort(cpu, "cpu_io_recompile: could not find TB for pc=%p", > @@ -1678,11 +1688,15 @@ void cpu_io_recompile(CPUState *cpu, uintptr_t retaddr) > /* FIXME: In theory this could raise an exception. In practice > we have already translated the block once so it's probably ok. */ > tb_gen_code(cpu, pc, cs_base, flags, cflags); > - /* TODO: If env->pc != tb->pc (i.e. the faulting instruction was not > - the first in the TB) then we end up generating a whole new TB and > - repeating the fault, which is horribly inefficient. > - Better would be to execute just this insn uncached, or generate a > - second new TB. */ > + > + /* This unlocks the tb_lock. > + * > + * TODO: If env->pc != tb->pc (i.e. the faulting instruction was not > + * the first in the TB) then we end up generating a whole new TB and > + * repeating the fault, which is horribly inefficient. > + * Better would be to execute just this insn uncached, or generate a > + * second new TB. > + */ > cpu_resume_from_signal(cpu, NULL); > } (snip) Kind regards, Sergey