Re: [PATCH v2 20/21] accel/tcg: allow plugin instrumentation to be disable via cflags

[Alex Bennée]

Aaron Lindsay <aaron@os.amperecomputing.com> writes:

> On Feb 12 16:04, Alex Bennée wrote:
>> Do you see two stores or one store? I think I got the sense the wrong
>> way around because the store is instrumented before the mmu code,
>> hence should be skipped on a re-instrumented block.
>
> I only see one store between the instruction callback for the store and
> the instruction callback for the subsequent instruction.

I've posted:

  Subject: [PATCH  v3 00/23] plugins/next pre-PR (hwprofile, regression fixes, 
icount count fix)
  Date: Sat, 13 Feb 2021 13:03:02 +0000
  Message-Id: <20210213130325.14781-1-alex.bennee@linaro.org>

which I think solves it. Could you have a look?

>
> -Aaron
>
>> On Fri, 12 Feb 2021 at 15:41, Aaron Lindsay
>> <aaron@os.amperecomputing.com> wrote:
>> >
>> > On Feb 12 14:43, Alex Bennée wrote:
>> > > Aaron Lindsay <aaron@os.amperecomputing.com> writes:
>> > > > On Feb 10 22:10, Alex Bennée wrote:
>> > > >> When icount is enabled and we recompile an MMIO access we end up
>> > > >> double counting the instruction execution. To avoid this we introduce
>> > > >> the CF_NOINSTR cflag which disables instrumentation for the next TB.
>> > > >> As this is part of the hashed compile flags we will only execute the
>> > > >> generated TB while coming out of a cpu_io_recompile.
>> > > >
>> > > > Unfortunately this patch works a little too well!
>> > > >
>> > > > With this change, the memory access callbacks registered via
>> > > > `qemu_plugin_register_vcpu_mem_cb()` are never called for the
>> > > > re-translated instruction making the IO access, since we've disabled 
>> > > > all
>> > > > instrumentation.
>> > > >
>> > > > Is it possible to selectively disable only instruction callbacks using
>> > > > this mechanism, while still allowing others that would not yet have 
>> > > > been
>> > > > called for the re-translated instruction?
>> > >
>> > > Can you try the following fugly patch on top of this series:
>> >
>> > This patch does allow me to successfully observe memory callbacks for
>> > stores in this case. It seems from looking at the patch that you
>> > intentionally only allowed memory callbacks for stores in this case, and
>> > I still don't see callbacks any for loads.
>> >
>> > -Aaron
>> >
>> > > --8<---------------cut here---------------start------------->8---
>> > > diff --git a/include/exec/plugin-gen.h b/include/exec/plugin-gen.h
>> > > index 4834a9e2f4..b1b72b5d90 100644
>> > > --- a/include/exec/plugin-gen.h
>> > > +++ b/include/exec/plugin-gen.h
>> > > @@ -19,7 +19,7 @@ struct DisasContextBase;
>> > >
>> > >  #ifdef CONFIG_PLUGIN
>> > >
>> > > -bool plugin_gen_tb_start(CPUState *cpu, const TranslationBlock *tb);
>> > > +bool plugin_gen_tb_start(CPUState *cpu, const TranslationBlock *tb, 
>> > > bool supress);
>> > >  void plugin_gen_tb_end(CPUState *cpu);
>> > >  void plugin_gen_insn_start(CPUState *cpu, const struct DisasContextBase 
>> > > *db);
>> > >  void plugin_gen_insn_end(void);
>> > > @@ -41,7 +41,7 @@ static inline void plugin_insn_append(const void 
>> > > *from, size_t size)
>> > >  #else /* !CONFIG_PLUGIN */
>> > >
>> > >  static inline
>> > > -bool plugin_gen_tb_start(CPUState *cpu, const TranslationBlock *tb)
>> > > +bool plugin_gen_tb_start(CPUState *cpu, const TranslationBlock *tb, 
>> > > bool supress)
>> > >  {
>> > >      return false;
>> > >  }
>> > > diff --git a/include/qemu/plugin.h b/include/qemu/plugin.h
>> > > index 841deed79c..2a26a2277f 100644
>> > > --- a/include/qemu/plugin.h
>> > > +++ b/include/qemu/plugin.h
>> > > @@ -92,6 +92,7 @@ struct qemu_plugin_dyn_cb {
>> > >      };
>> > >  };
>> > >
>> > > +/* Internal context for instrumenting an instruction */
>> > >  struct qemu_plugin_insn {
>> > >      GByteArray *data;
>> > >      uint64_t vaddr;
>> > > @@ -99,6 +100,7 @@ struct qemu_plugin_insn {
>> > >      GArray *cbs[PLUGIN_N_CB_TYPES][PLUGIN_N_CB_SUBTYPES];
>> > >      bool calls_helpers;
>> > >      bool mem_helper;
>> > > +    bool store_only;
>> > >  };
>> > >
>> > >  /*
>> > > @@ -128,6 +130,7 @@ static inline struct qemu_plugin_insn 
>> > > *qemu_plugin_insn_alloc(void)
>> > >      return insn;
>> > >  }
>> > >
>> > > +/* Internal context for this TranslationBlock */
>> > >  struct qemu_plugin_tb {
>> > >      GPtrArray *insns;
>> > >      size_t n;
>> > > @@ -135,6 +138,7 @@ struct qemu_plugin_tb {
>> > >      uint64_t vaddr2;
>> > >      void *haddr1;
>> > >      void *haddr2;
>> > > +    bool store_only;
>> > >      GArray *cbs[PLUGIN_N_CB_SUBTYPES];
>> > >  };
>> > >
>> > > diff --git a/accel/tcg/plugin-gen.c b/accel/tcg/plugin-gen.c
>> > > index 8a1bb801e0..137b91282e 100644
>> > > --- a/accel/tcg/plugin-gen.c
>> > > +++ b/accel/tcg/plugin-gen.c
>> > > @@ -842,7 +842,7 @@ static void plugin_gen_inject(const struct 
>> > > qemu_plugin_tb *plugin_tb)
>> > >      pr_ops();
>> > >  }
>> > >
>> > > -bool plugin_gen_tb_start(CPUState *cpu, const TranslationBlock *tb)
>> > > +bool plugin_gen_tb_start(CPUState *cpu, const TranslationBlock *tb, 
>> > > bool store_only)
>> > >  {
>> > >      struct qemu_plugin_tb *ptb = tcg_ctx->plugin_tb;
>> > >      bool ret = false;
>> > > @@ -855,6 +855,7 @@ bool plugin_gen_tb_start(CPUState *cpu, const 
>> > > TranslationBlock *tb)
>> > >          ptb->vaddr2 = -1;
>> > >          get_page_addr_code_hostp(cpu->env_ptr, tb->pc, &ptb->haddr1);
>> > >          ptb->haddr2 = NULL;
>> > > +        ptb->store_only = store_only;
>> > >
>> > >          plugin_gen_empty_callback(PLUGIN_GEN_FROM_TB);
>> > >      }
>> > > diff --git a/accel/tcg/translator.c b/accel/tcg/translator.c
>> > > index 14d1ea795d..082f2c8ee1 100644
>> > > --- a/accel/tcg/translator.c
>> > > +++ b/accel/tcg/translator.c
>> > > @@ -58,7 +58,7 @@ void translator_loop(const TranslatorOps *ops, 
>> > > DisasContextBase *db,
>> > >      ops->tb_start(db, cpu);
>> > >      tcg_debug_assert(db->is_jmp == DISAS_NEXT);  /* no early exit */
>> > >
>> > > -    plugin_enabled = !(tb_cflags(db->tb) & CF_NOINSTR) && 
>> > > plugin_gen_tb_start(cpu, tb);
>> > > +    plugin_enabled = plugin_gen_tb_start(cpu, tb, tb_cflags(db->tb) & 
>> > > CF_NOINSTR);
>> > >
>> > >      while (true) {
>> > >          db->num_insns++;
>> > > @@ -100,6 +100,8 @@ void translator_loop(const TranslatorOps *ops, 
>> > > DisasContextBase *db,
>> > >              gen_io_start();
>> > >              ops->translate_insn(db, cpu);
>> > >          } else {
>> > > +            /* we should only see NOINSTR for io_recompile */
>> > > +            g_assert(!(tb_cflags(db->tb) & CF_NOINSTR));
>> > >              ops->translate_insn(db, cpu);
>> > >          }
>> > >
>> > > diff --git a/plugins/api.c b/plugins/api.c
>> > > index 5dc8e6f934..ac8475707d 100644
>> > > --- a/plugins/api.c
>> > > +++ b/plugins/api.c
>> > > @@ -84,15 +84,19 @@ void qemu_plugin_register_vcpu_tb_exec_cb(struct 
>> > > qemu_plugin_tb *tb,
>> > >                                            enum qemu_plugin_cb_flags 
>> > > flags,
>> > >                                            void *udata)
>> > >  {
>> > > -    plugin_register_dyn_cb__udata(&tb->cbs[PLUGIN_CB_REGULAR],
>> > > -                                  cb, flags, udata);
>> > > +    if (!tb->store_only) {
>> > > +        plugin_register_dyn_cb__udata(&tb->cbs[PLUGIN_CB_REGULAR],
>> > > +                                      cb, flags, udata);
>> > > +    }
>> > >  }
>> > >
>> > >  void qemu_plugin_register_vcpu_tb_exec_inline(struct qemu_plugin_tb *tb,
>> > >                                                enum qemu_plugin_op op,
>> > >                                                void *ptr, uint64_t imm)
>> > >  {
>> > > -    plugin_register_inline_op(&tb->cbs[PLUGIN_CB_INLINE], 0, op, ptr, 
>> > > imm);
>> > > +    if (!tb->store_only) {
>> > > +        plugin_register_inline_op(&tb->cbs[PLUGIN_CB_INLINE], 0, op, 
>> > > ptr, imm);
>> > > +    }
>> > >  }
>> > >
>> > >  void qemu_plugin_register_vcpu_insn_exec_cb(struct qemu_plugin_insn 
>> > > *insn,
>> > > @@ -100,16 +104,20 @@ void qemu_plugin_register_vcpu_insn_exec_cb(struct 
>> > > qemu_plugin_insn *insn,
>> > >                                              enum qemu_plugin_cb_flags 
>> > > flags,
>> > >                                              void *udata)
>> > >  {
>> > > -    
>> > > plugin_register_dyn_cb__udata(&insn->cbs[PLUGIN_CB_INSN][PLUGIN_CB_REGULAR],
>> > > -        cb, flags, udata);
>> > > +    if (!insn->store_only) {
>> > > +        
>> > > plugin_register_dyn_cb__udata(&insn->cbs[PLUGIN_CB_INSN][PLUGIN_CB_REGULAR],
>> > > +                                      cb, flags, udata);
>> > > +    }
>> > >  }
>> > >
>> > >  void qemu_plugin_register_vcpu_insn_exec_inline(struct qemu_plugin_insn 
>> > > *insn,
>> > >                                                  enum qemu_plugin_op op,
>> > >                                                  void *ptr, uint64_t imm)
>> > >  {
>> > > -    
>> > > plugin_register_inline_op(&insn->cbs[PLUGIN_CB_INSN][PLUGIN_CB_INLINE],
>> > > -                              0, op, ptr, imm);
>> > > +    if (!insn->store_only) {
>> > > +        
>> > > plugin_register_inline_op(&insn->cbs[PLUGIN_CB_INSN][PLUGIN_CB_INLINE],
>> > > +                                  0, op, ptr, imm);
>> > > +    }
>> > >  }
>> > >
>> > >
>> > > @@ -120,8 +128,13 @@ void qemu_plugin_register_vcpu_mem_cb(struct 
>> > > qemu_plugin_insn *insn,
>> > >                                        enum qemu_plugin_mem_rw rw,
>> > >                                        void *udata)
>> > >  {
>> > > -    
>> > > plugin_register_vcpu_mem_cb(&insn->cbs[PLUGIN_CB_MEM][PLUGIN_CB_REGULAR],
>> > > -                                cb, flags, rw, udata);
>> > > +    if (insn->store_only && (rw & QEMU_PLUGIN_MEM_W)) {
>> > > +        
>> > > plugin_register_vcpu_mem_cb(&insn->cbs[PLUGIN_CB_MEM][PLUGIN_CB_REGULAR],
>> > > +                                    cb, flags, QEMU_PLUGIN_MEM_W, 
>> > > udata);
>> > > +    } else {
>> > > +        
>> > > plugin_register_vcpu_mem_cb(&insn->cbs[PLUGIN_CB_MEM][PLUGIN_CB_REGULAR],
>> > > +                                    cb, flags, rw, udata);
>> > > +    }
>> > >  }
>> > >
>> > >  void qemu_plugin_register_vcpu_mem_inline(struct qemu_plugin_insn *insn,
>> > > @@ -129,8 +142,10 @@ void qemu_plugin_register_vcpu_mem_inline(struct 
>> > > qemu_plugin_insn *insn,
>> > >                                            enum qemu_plugin_op op, void 
>> > > *ptr,
>> > >                                            uint64_t imm)
>> > >  {
>> > > -    
>> > > plugin_register_inline_op(&insn->cbs[PLUGIN_CB_MEM][PLUGIN_CB_INLINE],
>> > > -        rw, op, ptr, imm);
>> > > +    if (!insn->store_only) {
>> > > +        
>> > > plugin_register_inline_op(&insn->cbs[PLUGIN_CB_MEM][PLUGIN_CB_INLINE],
>> > > +                                  rw, op, ptr, imm);
>> > > +    }
>> > >  }
>> > >
>> > >  void qemu_plugin_register_vcpu_tb_trans_cb(qemu_plugin_id_t id,
>> > > @@ -181,10 +196,13 @@ uint64_t qemu_plugin_tb_vaddr(const struct 
>> > > qemu_plugin_tb *tb)
>> > >  struct qemu_plugin_insn *
>> > >  qemu_plugin_tb_get_insn(const struct qemu_plugin_tb *tb, size_t idx)
>> > >  {
>> > > +    struct qemu_plugin_insn *insn;
>> > >      if (unlikely(idx >= tb->n)) {
>> > >          return NULL;
>> > >      }
>> > > -    return g_ptr_array_index(tb->insns, idx);
>> > > +    insn = g_ptr_array_index(tb->insns, idx);
>> > > +    insn->store_only = tb->store_only;
>> > > +    return insn;
>> > >  }
>> > >
>> > >  /*
>> > > --8<---------------cut here---------------end--------------->8---
>> > >
>> > > --
>> > > Alex Bennée
>> 
>> 
>> 
>> -- 
>> Alex Bennée
>> KVM/QEMU Hacker for Linaro


-- 
Alex Bennée