Re: [PATCH 12/18] accel/tcg: inline cpu_exit()

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 29 Aug 2025 17:31:09 +0200
Paolo Bonzini <pbonzini@redhat.com> wrote:

> Right now, cpu_exit() is not usable from all accelerators because it
> includes a TCG-specific thread kick.  In fact, cpu_exit() doubles as
> the TCG thread-kick via tcg_kick_vcpu_thread().
> 
> In preparation for changing that, inline cpu_exit() into
> tcg_kick_vcpu_thread().  The direction of the calls can then be
> reversed, with an accelerator-independent cpu_exit() calling into
> qemu_vcpu_kick() rather than the opposite.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reviewed-by: Igor Mammedov <imammedo@redhat.com>

> ---
>  accel/tcg/cpu-exec.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
> index 9241bcadb5f..3ae545e888f 100644
> --- a/accel/tcg/cpu-exec.c
> +++ b/accel/tcg/cpu-exec.c
> @@ -751,7 +751,16 @@ static inline bool cpu_handle_exception(CPUState *cpu, int *ret)
>  
>  void tcg_kick_vcpu_thread(CPUState *cpu)
>  {
> -    cpu_exit(cpu);
> +    /*
> +     * Ensure cpu_exec will see the reason why the exit request was set.
> +     * FIXME: this is not always needed.  Other accelerators instead
> +     * read interrupt_request and set exit_request on demand from the
> +     * CPU thread; see kvm_arch_pre_run() for example.
> +     */
> +    qatomic_store_release(&cpu->exit_request, true);
> +
> +    /* Ensure cpu_exec will see the exit request after TCG has exited.  */
> +    qatomic_store_release(&cpu->neg.icount_decr.u16.high, -1);
>  }
>  
>  static inline bool icount_exit_request(CPUState *cpu)
> @@ -780,7 +789,8 @@ static inline bool cpu_handle_interrupt(CPUState *cpu,
>      /* Clear the interrupt flag now since we're processing
>       * cpu->interrupt_request and cpu->exit_request.
>       * Ensure zeroing happens before reading cpu->exit_request or
> -     * cpu->interrupt_request (see also smp_wmb in cpu_exit())
> +     * cpu->interrupt_request (see also store-release in
> +     * tcg_kick_vcpu_thread())
>       */
>      qatomic_set_mb(&cpu->neg.icount_decr.u16.high, 0);
>