Subject: [PATCH v2 5/6] arm/arm64: KVM: Turn off vcpus on PSCI shutdown/reboot

From: [email-masked] (Marc Zyngier)
Date: Mon, 08 Dec 2014 12:04:53 +0000

On 03/12/14 21:18, Christoffer Dall wrote:
> When a vcpu calls SYSTEM_OFF or SYSTEM_RESET with PSCI v0.2, the vcpus
> should really be turned off for the VM adhering to the suggestions in
> the PSCI spec, and it's the sane thing to do.
> 
> Also, clarify the behavior and expectations for exits to user space with
> the KVM_EXIT_SYSTEM_EVENT case.
> 
> Signed-off-by: Christoffer Dall <[email-masked]>
> ---
>  Documentation/virtual/kvm/api.txt |  9 +++++++++
>  arch/arm/kvm/psci.c               | 19 +++++++++++++++++++
>  arch/arm64/include/asm/kvm_host.h |  1 +
>  3 files changed, 29 insertions(+)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index 81f1b97..228f9cf 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -2957,6 +2957,15 @@ HVC instruction based PSCI call from the vcpu. The 'type' field describes
>  the system-level event type. The 'flags' field describes architecture
>  specific flags for the system-level event.
>  
> +Valid values for 'type' are:
> +  KVM_SYSTEM_EVENT_SHUTDOWN -- the guest has requested a shutdown of the
> +   VM. Userspace is not obliged to honour this, and if it does honour
> +   this does not need to destroy the VM synchronously (ie it may call
> +   KVM_RUN again before shutdown finally occurs).
> +  KVM_SYSTEM_EVENT_RESET -- the guest has requested a reset of the VM.
> +   As with SHUTDOWN, userspace can choose to ignore the request, or
> +   to schedule the reset to occur in the future and may call KVM_RUN again.
> +
>  		/* Fix the size of the union. */
>  		char padding[256];
>  	};
> diff --git a/arch/arm/kvm/psci.c b/arch/arm/kvm/psci.c
> index 09cf377..ae0bb91 100644
> --- a/arch/arm/kvm/psci.c
> +++ b/arch/arm/kvm/psci.c
> @@ -15,6 +15,7 @@
>   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
>   */
>  
> +#include <linux/preempt.h>
>  #include <linux/kvm_host.h>
>  #include <linux/wait.h>
>  
> @@ -166,6 +167,24 @@ static unsigned long kvm_psci_vcpu_affinity_info(struct kvm_vcpu *vcpu)
>  
>  static void kvm_prepare_system_event(struct kvm_vcpu *vcpu, u32 type)
>  {
> +	int i;
> +	struct kvm_vcpu *tmp;
> +
> +	/*
> +	 * The KVM ABI specifies that a system event exit may call KVM_RUN
> +	 * again and may perform shutdown/reboot at a later time that when the
> +	 * actual request is made.  Since we are implementing PSCI and a
> +	 * caller of PSCI reboot and shutdown expects that the system shuts
> +	 * down or reboots immediately, let's make sure that VCPUs are not run
> +	 * after this call is handled and before the VCPUs have been
> +	 * re-initialized.
> +	 */
> +	kvm_for_each_vcpu(i, tmp, vcpu->kvm)
> +		tmp->arch.pause = true;
> +	preempt_disable();
> +	force_vm_exit(cpu_all_mask);
> +	preempt_enable();
> +

I'm slightly uneasy about this force_vm_exit, as this is something that
is directly triggered by the guest. I suppose it is almost impossible to
find out which CPUs we're actually using...

>  	memset(&vcpu->run->system_event, 0, sizeof(vcpu->run->system_event));
>  	vcpu->run->system_event.type = type;
>  	vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 65c6152..0b7dfdb 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -198,6 +198,7 @@ struct kvm_vcpu *kvm_arm_get_running_vcpu(void);
>  struct kvm_vcpu * __percpu *kvm_get_running_vcpus(void);
>  
>  u64 kvm_call_hyp(void *hypfn, ...);
> +void force_vm_exit(const cpumask_t *mask);
>  
>  int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  		int exception_index);
> 

Other than that,

Acked-by: Marc Zyngier <[email-masked]>

	M.
-- 
Jazz is not dead. It just smells funny...