Re: [PATCH 11/16] accel/kvm: Consistently return CPU halt state from process_async_events

[Paolo Bonzini <pbonzini@redhat.com>]

On 8/13/26 20:16, Philippe Mathieu-Daudé wrote:
> When comparing the KVM implementations, RISCV and ARM differ
> from S390x / PPC and LoongArch. The caller expects a non-zero
> value to return pausing execution with the EXCP_HLT exception:
> 
>    3427 int kvm_cpu_exec(CPUState *cpu)
>    3428 {
>    ...
>    3434     if (kvm_arch_process_async_events(cpu)) {
>    3435         return EXCP_HLT;
>    3436     }
>    3437
>    3438     bql_unlock();
>    3439     cpu_exec_start(cpu);
>    3440
>    3441     /* Inner vCPU loop */
>    3442     do {
>    ...

Your patch is correct because, even if cpu_thread_is_idle() sees 
cpu->halted == false, the flag could become true during 
process_queued_cpu_work() because it releases the BQL.

However, I think the better fix is to remove the return code, and check 
cpu->halted in kvm_cpu_exec().

Thanks,

Paolo

> Change ARM and RISC-V to return cs->halted for consistent behavior.
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
> ---
>   target/arm/kvm.c           | 2 +-
>   target/riscv/kvm/kvm-cpu.c | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index d40a6a98591..5caabfab63f 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -1575,7 +1575,7 @@ bool kvm_arch_stop_on_emulation_error(CPUState *cs)
>   
>   int kvm_arch_process_async_events(CPUState *cs)
>   {
> -    return 0;
> +    return cs->halted;
>   }
>   
>   /**
> diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
> index 97069bf597a..1a61cd5ef37 100644
> --- a/target/riscv/kvm/kvm-cpu.c
> +++ b/target/riscv/kvm/kvm-cpu.c
> @@ -1568,7 +1568,7 @@ int kvm_arch_irqchip_create(KVMState *s)
>   
>   int kvm_arch_process_async_events(CPUState *cs)
>   {
> -    return 0;
> +    return cs->halted;
>   }
>   
>   void kvm_arch_pre_run(CPUState *cs, struct kvm_run *run)