Re: [Qemu-devel] [RFC 01/10] exec: Introduce tcg_exclusive_{lock, unlock}()

["Alex Bennée" <alex.bennee@linaro.org>]

Alvise Rigo <a.rigo@virtualopensystems.com> writes:

> Add tcg_exclusive_{lock,unlock}() functions that will be used for making
> the emulation of LL and SC instructions thread safe.

I wonder how much similarity there is to the mechanism linus-user ends
up using for it's exclusive-start/end?

>
> Signed-off-by: Alvise Rigo <a.rigo@virtualopensystems.com>
> ---
>  cpus.c            |  2 ++
>  exec.c            | 18 ++++++++++++++++++
>  include/qom/cpu.h |  5 +++++
>  3 files changed, 25 insertions(+)
>
> diff --git a/cpus.c b/cpus.c
> index 860e7ba..b9ec903 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -961,6 +961,8 @@ void qemu_init_cpu_loop(void)
>      qemu_cond_init(&qemu_work_cond);
>      qemu_mutex_init(&qemu_global_mutex);
>
> +    qemu_spin_init(&cpu_exclusive_lock);
> +
>      qemu_thread_get_self(&io_thread);
>
>      safe_work = g_array_sized_new(TRUE, TRUE, sizeof(qemu_safe_work_item), 128);
> diff --git a/exec.c b/exec.c
> index a24b31c..1c72113 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -197,6 +197,24 @@ void cpu_exclusive_history_free(void)
>          g_free(excl_history.c_array);
>      }
>  }
> +
> +__thread bool cpu_have_exclusive_lock;
> +QemuSpin cpu_exclusive_lock;
> +inline void tcg_exclusive_lock(void)
> +{
> +    if (!cpu_have_exclusive_lock) {
> +        qemu_spin_lock(&cpu_exclusive_lock);
> +        cpu_have_exclusive_lock = true;
> +    }
> +}
> +
> +inline void tcg_exclusive_unlock(void)
> +{
> +    if (cpu_have_exclusive_lock) {
> +        cpu_have_exclusive_lock = false;
> +        qemu_spin_unlock(&cpu_exclusive_lock);
> +    }
> +}
>  #endif
>
>  #if !defined(CONFIG_USER_ONLY)
> diff --git a/include/qom/cpu.h b/include/qom/cpu.h
> index 0f51870..019f06d 100644
> --- a/include/qom/cpu.h
> +++ b/include/qom/cpu.h
> @@ -201,6 +201,11 @@ typedef struct CPUClass {
>      void (*disas_set_info)(CPUState *cpu, disassemble_info *info);
>  } CPUClass;
>
> +/* Protect cpu_exclusive_* variable .*/
> +void tcg_exclusive_lock(void);
> +void tcg_exclusive_unlock(void);
> +extern QemuSpin cpu_exclusive_lock;
> +
>  #ifdef HOST_WORDS_BIGENDIAN
>  typedef struct icount_decr_u16 {
>      uint16_t high;


--
Alex Bennée