[v2] accel, cpus: clean up cpu->exit_request

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

Paolo Bonzini posted 18 patches 1 week ago

Diff against v1
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Maintainers: Richard Henderson <richard.henderson@linaro.org>, Paolo Bonzini <pbonzini@redhat.com>, "Philippe Mathieu-Daudé" <philmd@linaro.org>, Cameron Esfahani <dirty@apple.com>, Roman Bolshakov <rbolshakov@ddn.com>, Phil Dennis-Jordan <phil@philjordan.eu>, Mads Ynddal <mads@ynddal.dk>, Riku Voipio <riku.voipio@iki.fi>, Warner Losh <imp@bsdimp.com>, Kyle Evans <kevans@freebsd.org>, Eduardo Habkost <eduardo@habkost.net>, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, Yanan Wang <wangyanan55@huawei.com>, Zhao Liu <zhao1.liu@intel.com>, Nicholas Piggin <npiggin@gmail.com>, Chinmay Rath <rathc@linux.ibm.com>, Harsh Prateek Bora <harshpb@linux.ibm.com>, Laurent Vivier <laurent@vivier.eu>, Brian Cain <brian.cain@oss.qualcomm.com>, "Alex Bennée" <alex.bennee@linaro.org>, Peter Maydell <peter.maydell@linaro.org>, Michael Rolnik <mrolnik@gmail.com>, Marcelo Tosatti <mtosatti@redhat.com>, Reinoud Zandijk <reinoud@netbsd.org>, Sunil Muthuswamy <sunilmut@microsoft.com>, Stafford Horne <shorne@gmail.com>, Yoshinori Sato <yoshinori.sato@nifty.com>, David Hildenbrand <david@redhat.com>, Ilya Leoshkevich <iii@linux.ibm.com>, Thomas Huth <thuth@redhat.com>, Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>, Artyom Tarasenko <atar4qemu@gmail.com>

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

Posted by Paolo Bonzini 1 week ago

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>
---
 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);
 
-- 
2.51.0

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

Posted by Igor Mammedov 4 days, 14 hours ago

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);
>

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

Posted by Richard Henderson 1 week ago

On 8/30/25 01:31, Paolo Bonzini 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>
> ---
>   accel/tcg/cpu-exec.c | 14 ++++++++++++--
>   1 file changed, 12 insertions(+), 2 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~