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

[Alex Bennée]

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.

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