> From: Richard Henderson [mailto:richard.hender...@linaro.org] > On 27 February 2018 at 17:53, Pavel Dovgalyuk <pavel.dovga...@ispras.ru> > wrote: > > > > cpu_io_recompile() function was broken by > > the commit 9b990ee5a3cc6aa38f81266fb0c6ef37a36c45b9. Instead of regenerating > > the block starting from PC of the original block, it just set the > > instruction > > counter for TCG. In most cases this was unnoticed, but in icount mode > > there was an exception for incorrect usage of CF_LAST_IO flag. > > This patch recovers recompilation of the original block and also > > configures translation for executing single IO instruction which > > caused a recompilation. > > > > Signed-off-by: Pavel Dovgalyuk <pavel.dovga...@ispras.ru> > > --- > > accel/tcg/translate-all.c | 18 +++++++++++++++--- > > 1 file changed, 15 insertions(+), 3 deletions(-) > > > > diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c > > index 67795cd..5ad1b91 100644 > > --- a/accel/tcg/translate-all.c > > +++ b/accel/tcg/translate-all.c > > @@ -1728,7 +1728,8 @@ void cpu_io_recompile(CPUState *cpu, uintptr_t > > retaddr) > > CPUArchState *env = cpu->env_ptr; > > #endif > > TranslationBlock *tb; > > - uint32_t n; > > + uint32_t n, flags; > > + target_ulong pc, cs_base; > > > > tb_lock(); > > tb = tb_find_pc(retaddr); > > @@ -1766,8 +1767,14 @@ void cpu_io_recompile(CPUState *cpu, uintptr_t > > retaddr) > > cpu_abort(cpu, "TB too big during recompile"); > > } > > > > - /* Adjust the execution state of the next TB. */ > > - cpu->cflags_next_tb = curr_cflags() | CF_LAST_IO | n; > > + pc = tb->pc; > > + cs_base = tb->cs_base; > > + flags = tb->flags; > > + tb_phys_invalidate(tb, -1); > > + > > + /* Execute one IO instruction without caching > > + instead of creating large TB. */ > > + cpu->cflags_next_tb = curr_cflags() | CF_LAST_IO | CF_NOCACHE | 1; > > > > if (tb->cflags & CF_NOCACHE) { > > if (tb->orig_tb) { > > @@ -1778,6 +1785,11 @@ void cpu_io_recompile(CPUState *cpu, uintptr_t > > retaddr) > > tb_remove(tb); > > } > > > > + /* Generate new TB instead of the current one. */ > > + /* 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, curr_cflags() | CF_LAST_IO | n); > > This isn't right. The whole point of the patch that you reference as > having broken > things is that calls to tb_gen_code which ignore their return value > are by definition > relying on the side effect of altering the TB cache, and are therefore > by definition racy.
I see. > That is exactly the point of cpu->cflags_next_tb, that when we next > arrive in cpu_exec > we look up (or generate) the next TB with the given flags. At which > point we will *not* > be relying on the TB cache, and we'll execute the generated TB right away. Well, as a ineffective solution, we can just omit tb_gen_code, but still make + cpu->cflags_next_tb = curr_cflags() | CF_LAST_IO | CF_NOCACHE | 1; Then the recompilation will occur every time, because the translation for the original address is not limited by some counter. > I do not have enough context within this patch to determine what the > proper solution is. The context is here: https://lists.gnu.org/archive/html/qemu-devel/2018-02/msg04818.html Pavel Dovgalyuk
