icount: fix cpu_restore_state_from_tb for non-tb-exit cases

In icount mode, instructions that access io memory spaces in the middle
of the translation block invoke TB recompilation.  After recompilation,
such instructions become last in the TB and are allowed to access io
memory spaces.

When the code includes instruction like i386 'xchg eax, 0xffffd080'
which accesses APIC, QEMU goes into an infinite loop of the recompilation.

This instruction includes two memory accesses - one read and one write.
After the first access, APIC calls cpu_report_tpr_access, which restores
the CPU state to get the current eip.  But cpu_restore_state_from_tb
resets the cpu->can_do_io flag which makes the second memory access invalid.
Therefore the second memory access causes a recompilation of the block.
Then these operations repeat again and again.

This patch moves resetting cpu->can_do_io flag from
cpu_restore_state_from_tb to cpu_loop_exit* functions.

It also adds a parameter for cpu_restore_state which controls restoring
icount.  There is no need to restore icount when we only query CPU state
without breaking the TB.  Restoring it in such cases leads to the
incorrect flow of the virtual time.

In most cases new parameter is true (icount should be recalculated).
But there are two cases in i386 and openrisc when the CPU state is only
queried without the need to break the TB.  This patch fixes both of
these cases.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Message-Id: <20180409091320.12504.35329.stgit@pasha-VirtualBox>
[rth: Make can_do_io setting unconditional; move from cpu_exec;
make cpu_loop_exit_{noexc,restore} call cpu_loop_exit.]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

4 files changed, 20 insertions, 20 deletions

diff --git a/accel/tcg/cpu-exec-common.c b/accel/tcg/cpu-exec-common.c
index dac5aac..2988fde 100644
--- a/accel/tcg/cpu-exec-common.c
+++ b/accel/tcg/cpu-exec-common.c
@@ -27,10 +27,8 @@ bool tcg_allowed;
 /* exit the current TB, but without causing any exception to be raised */
 void cpu_loop_exit_noexc(CPUState *cpu)
 {
-    /* XXX: restore cpu registers saved in host registers */
-
     cpu->exception_index = -1;
-    siglongjmp(cpu->jmp_env, 1);
+    cpu_loop_exit(cpu);
 }
 
 #if defined(CONFIG_SOFTMMU)
@@ -65,15 +63,17 @@ void cpu_reloading_memory_map(void)
 
 void cpu_loop_exit(CPUState *cpu)
 {
+    /* Undo the setting in cpu_tb_exec.  */
+    cpu->can_do_io = 1;
     siglongjmp(cpu->jmp_env, 1);
 }
 
 void cpu_loop_exit_restore(CPUState *cpu, uintptr_t pc)
 {
     if (pc) {
-        cpu_restore_state(cpu, pc);
+        cpu_restore_state(cpu, pc, true);
     }
-    siglongjmp(cpu->jmp_env, 1);
+    cpu_loop_exit(cpu);
 }
 
 void cpu_loop_exit_atomic(CPUState *cpu, uintptr_t pc)
diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
index 9cc6972..81153e7 100644
--- a/accel/tcg/cpu-exec.c
+++ b/accel/tcg/cpu-exec.c
@@ -704,7 +704,6 @@ int cpu_exec(CPUState *cpu)
         g_assert(cpu == current_cpu);
         g_assert(cc == CPU_GET_CLASS(cpu));
 #endif /* buggy compiler */
-        cpu->can_do_io = 1;
         tb_lock_reset();
         if (qemu_mutex_iothread_locked()) {
             qemu_mutex_unlock_iothread();
diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
index d419060..f409d42 100644
--- a/accel/tcg/translate-all.c
+++ b/accel/tcg/translate-all.c
@@ -299,9 +299,11 @@ static int encode_search(TranslationBlock *tb, uint8_t *block)
 
 /* The cpu state corresponding to 'searched_pc' is restored.
  * Called with tb_lock held.
+ * When reset_icount is true, current TB will be interrupted and
+ * icount should be recalculated.
  */
 static int cpu_restore_state_from_tb(CPUState *cpu, TranslationBlock *tb,
-                                     uintptr_t searched_pc)
+                                     uintptr_t searched_pc, bool reset_icount)
 {
     target_ulong data[TARGET_INSN_START_WORDS] = { tb->pc };
     uintptr_t host_pc = (uintptr_t)tb->tc.ptr;
@@ -333,14 +335,12 @@ static int cpu_restore_state_from_tb(CPUState *cpu, TranslationBlock *tb,
     return -1;
 
  found:
-    if (tb->cflags & CF_USE_ICOUNT) {
+    if (reset_icount && (tb->cflags & CF_USE_ICOUNT)) {
         assert(use_icount);
-        /* Reset the cycle counter to the start of the block.  */
-        cpu->icount_decr.u16.low += num_insns;
-        /* Clear the IO flag.  */
-        cpu->can_do_io = 0;
+        /* Reset the cycle counter to the start of the block
+           and shift if to the number of actually executed instructions */
+        cpu->icount_decr.u16.low += num_insns - i;
     }
-    cpu->icount_decr.u16.low -= i;
     restore_state_to_opc(env, tb, data);
 
 #ifdef CONFIG_PROFILER
@@ -351,7 +351,7 @@ static int cpu_restore_state_from_tb(CPUState *cpu, TranslationBlock *tb,
     return 0;
 }
 
-bool cpu_restore_state(CPUState *cpu, uintptr_t host_pc)
+bool cpu_restore_state(CPUState *cpu, uintptr_t host_pc, bool will_exit)
 {
     TranslationBlock *tb;
     bool r = false;
@@ -377,7 +377,7 @@ bool cpu_restore_state(CPUState *cpu, uintptr_t host_pc)
         tb_lock();
         tb = tb_find_pc(host_pc);
         if (tb) {
-            cpu_restore_state_from_tb(cpu, tb, host_pc);
+            cpu_restore_state_from_tb(cpu, tb, host_pc, will_exit);
             if (tb->cflags & CF_NOCACHE) {
                 /* one-shot translation, invalidate it immediately */
                 tb_phys_invalidate(tb, -1);
@@ -1511,7 +1511,8 @@ void tb_invalidate_phys_page_range(tb_page_addr_t start, tb_page_addr_t end,
                 restore the CPU state */
 
                 current_tb_modified = 1;
-                cpu_restore_state_from_tb(cpu, current_tb, cpu->mem_io_pc);
+                cpu_restore_state_from_tb(cpu, current_tb,
+                                          cpu->mem_io_pc, true);
                 cpu_get_tb_cpu_state(env, &current_pc, &current_cs_base,
                                      &current_flags);
             }
@@ -1634,7 +1635,7 @@ static bool tb_invalidate_phys_page(tb_page_addr_t addr, uintptr_t pc)
                    restore the CPU state */
 
             current_tb_modified = 1;
-            cpu_restore_state_from_tb(cpu, current_tb, pc);
+            cpu_restore_state_from_tb(cpu, current_tb, pc, true);
             cpu_get_tb_cpu_state(env, &current_pc, &current_cs_base,
                                  &current_flags);
         }
@@ -1700,7 +1701,7 @@ void tb_check_watchpoint(CPUState *cpu)
     tb = tb_find_pc(cpu->mem_io_pc);
     if (tb) {
         /* We can use retranslation to find the PC.  */
-        cpu_restore_state_from_tb(cpu, tb, cpu->mem_io_pc);
+        cpu_restore_state_from_tb(cpu, tb, cpu->mem_io_pc, true);
         tb_phys_invalidate(tb, -1);
     } else {
         /* The exception probably happened in a helper.  The CPU state should
@@ -1736,7 +1737,7 @@ void cpu_io_recompile(CPUState *cpu, uintptr_t retaddr)
         cpu_abort(cpu, "cpu_io_recompile: could not find TB for pc=%p",
                   (void *)retaddr);
     }
-    cpu_restore_state_from_tb(cpu, tb, retaddr);
+    cpu_restore_state_from_tb(cpu, tb, retaddr, true);
 
     /* On MIPS and SH, delay slot instructions can only be restarted if
        they were already the first instruction in the TB.  If this is not
diff --git a/accel/tcg/user-exec.c b/accel/tcg/user-exec.c
index 7789958..26a3ffb 100644
--- a/accel/tcg/user-exec.c
+++ b/accel/tcg/user-exec.c
@@ -168,7 +168,7 @@ static inline int handle_cpu_signal(uintptr_t pc, siginfo_t *info,
     }
 
     /* Now we have a real cpu fault.  */
-    cpu_restore_state(cpu, pc);
+    cpu_restore_state(cpu, pc, true);
 
     sigprocmask(SIG_SETMASK, old_set, NULL);
     cpu_loop_exit(cpu);