On Wed, Aug 02, 2023 at 11:42:46PM +0000, 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 | 16 ++++++++++++++++
> 2 files changed, 19 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 1c566b3f21d6..9adc9d4f7841 100644
> --- a/kvm-cpu.c
> +++ b/kvm-cpu.c
> @@ -141,6 +141,22 @@ 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)
> +{
> + vcpu->paused = false;
> + kvm__continue(vcpu->kvm);
> +}
Why is it safe to manipulate 'vcpu->paused' here without the pause_lock
held? Relatedly, how does this interact with the 'pause' and 'resume'
lkvm commands?
Will
