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 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:

--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