In case when atomic operation is not supported, exit_atomic is called
and we stop the world and execute the atomic operation. This results
in a following call chain:

tcg_gen_atomic_cmpxchg_tl()
  -> gen_helper_exit_atomic()
     -> HELPER(exit_atomic)
        -> cpu_loop_exit_atomic() -> EXCP_ATOMIC
           -> qemu_tcg_cpu_thread_fn() => case EXCP_ATOMIC
              -> cpu_exec_step_atomic()
                 -> cpu_step_atomic()
                    -> cc->cpu_exec_enter() = ppc_cpu_exec_enter()
                       Sets env->reserve_addr = -1;

But by the time it return back, the reservation is erased and the code
fails, this continues forever and the lock is never taken.

Instead set this in powerpc_excp()

Now that ppc_cpu_exec_enter() doesn't have anything meaningful to do,
let us get rid of the function.

Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
---

Depends on following fix by Richard Henderson:
https://patchwork.ozlabs.org/patch/755582/

---

 target/ppc/excp_helper.c    | 3 +++
 target/ppc/translate_init.c | 9 ---------
 2 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/target/ppc/excp_helper.c b/target/ppc/excp_helper.c
index f4ee7aa..a6bcb47 100644
--- a/target/ppc/excp_helper.c
+++ b/target/ppc/excp_helper.c
@@ -728,6 +728,9 @@ static inline void powerpc_excp(PowerPCCPU *cpu, int excp_model, int excp)
     cs->exception_index = POWERPC_EXCP_NONE;
     env->error_code = 0;
 
+    /* Reset the reservation */
+    env->reserve_addr = -1;
+
     /* Any interrupt is context synchronizing, check if TCG TLB
      * needs a delayed flush on ppc64
      */
diff --git a/target/ppc/translate_init.c b/target/ppc/translate_init.c
index 77e5463..dc4239d 100644
--- a/target/ppc/translate_init.c
+++ b/target/ppc/translate_init.c
@@ -10426,14 +10426,6 @@ static bool ppc_cpu_has_work(CPUState *cs)
     return msr_ee && (cs->interrupt_request & CPU_INTERRUPT_HARD);
 }
 
-static void ppc_cpu_exec_enter(CPUState *cs)
-{
-    PowerPCCPU *cpu = POWERPC_CPU(cs);
-    CPUPPCState *env = &cpu->env;
-
-    env->reserve_addr = -1;
-}
-
 /* CPUClass::reset() */
 static void ppc_cpu_reset(CPUState *s)
 {
@@ -10650,7 +10642,6 @@ static void ppc_cpu_class_init(ObjectClass *oc, void *data)
     cc->get_phys_page_debug = ppc_cpu_get_phys_page_debug;
     cc->vmsd = &vmstate_ppc_cpu;
 #endif
-    cc->cpu_exec_enter = ppc_cpu_exec_enter;
 #if defined(CONFIG_SOFTMMU)
     cc->write_elf64_note = ppc64_cpu_write_elf64_note;
     cc->write_elf32_note = ppc32_cpu_write_elf32_note;
-- 
2.9.3

On 04/26/2017 08:29 PM, Nikunj A Dadhania wrote:
> @@ -728,6 +728,9 @@ static inline void powerpc_excp(PowerPCCPU *cpu, int excp_model, int excp)
>       cs->exception_index = POWERPC_EXCP_NONE;
>       env->error_code = 0;
>   
> +    /* Reset the reservation */
> +    env->reserve_addr = -1;
> +

It occurs to me that we might also need this in do_rfi, for transitioning back 
to userspace after the interrupt.


r~