Re: [PATCH kvmtool 12/21] Add helpers to pause the VM from vCPU thread

[Shaoqin Huang <shahuang@xxxxxxxxxx>]

Hi Oliver,

I have a play with this series, the guest always hang when hotplug two 
more cpus, it seems the kvm_cpu_continue_vm forget to continue the 
current cpu.

On 5/27/23 06:17, Oliver Upton wrote:
> Pausing the VM from a vCPU thread is perilous with the current helpers,
> as it waits indefinitely for a signal that never comes when invoked from
> a vCPU thread. Instead, add a helper for pausing the VM from a vCPU,
> working around the issue by explicitly marking the caller as paused
> before proceeding.
>
> Signed-off-by: Oliver Upton <oliver.upton@xxxxxxxxx>
> ---
>   include/kvm/kvm-cpu.h |  3 +++
>   kvm-cpu.c             | 15 +++++++++++++++
>   2 files changed, 18 insertions(+)
>
> diff --git a/include/kvm/kvm-cpu.h b/include/kvm/kvm-cpu.h
> index 0f16f8d6e872..9a4901bf94ca 100644
> --- a/include/kvm/kvm-cpu.h
> +++ b/include/kvm/kvm-cpu.h
> @@ -29,4 +29,7 @@ void kvm_cpu__show_page_tables(struct kvm_cpu *vcpu);
>   void kvm_cpu__arch_nmi(struct kvm_cpu *cpu);
>   void kvm_cpu__run_on_all_cpus(struct kvm *kvm, struct kvm_cpu_task *task);
>   
> +void kvm_cpu__pause_vm(struct kvm_cpu *vcpu);
> +void kvm_cpu__continue_vm(struct kvm_cpu *vcpu);
> +
>   #endif /* KVM__KVM_CPU_H */
> diff --git a/kvm-cpu.c b/kvm-cpu.c
> index 7dec08894cd3..9eb857b859c3 100644
> --- a/kvm-cpu.c
> +++ b/kvm-cpu.c
> @@ -141,6 +141,21 @@ void kvm_cpu__run_on_all_cpus(struct kvm *kvm, struct kvm_cpu_task *task)
>   	mutex_unlock(&task_lock);
>   }
>   
> +void kvm_cpu__pause_vm(struct kvm_cpu *vcpu)
> +{
> +	/*
> +	 * Mark the calling vCPU as paused to avoid waiting indefinitely for a
> +	 * signal exit.
> +	 */
> +	vcpu->paused = true;
> +	kvm__pause(vcpu->kvm);
> +}
> +
> +void kvm_cpu__continue_vm(struct kvm_cpu *vcpu)
> +{
Here should add:
	vcpu->paused = false;
> +	kvm__continue(vcpu->kvm);
> +}
> +
>   int kvm_cpu__start(struct kvm_cpu *cpu)
>   {
>   	sigset_t sigset;

--
Shaoqin