Subject: [PATCH v4 10/10] ARM/ARM64: KVM: Emulate PSCI v0.2 CPU_SUSPEND

From: [email-masked] (Christoffer Dall)
Date: Sun, 16 Mar 2014 20:41:30 -0700

On Thu, Feb 06, 2014 at 05:01:42PM +0530, Anup Patel wrote:
> This patch adds emulation of PSCI v0.2 CPU_SUSPEND function call for
> KVM ARM/ARM64. This is a VCPU-level function call which can suspend
> current VCPU or all VCPUs within current VCPU's affinity level.
> 
> The CPU_SUSPEND emulation is not tested much because currently there
> is no CPUIDLE driver in Linux kernel that uses PSCI CPU_SUSPEND. The
> PSCI CPU_SUSPEND implementation in ARM64 kernel was tested using a
> Simple CPUIDLE driver which is not published due to unstable DT-bindings
> for PSCI.
> (For more info, http://lwn.net/Articles/574950/)
> 
> Even if we had stable DT-bindings for PSCI and CPUIDLE driver that
> uses PSCI CPU_SUSPEND then still we need to define SUSPEND states
> for KVM ARM/ARM64. Due to this, the CPU_SUSPEND emulation added
> by this patch only pause a VCPU and to wakeup a VCPU we need to
> explicity call PSCI CPU_ON from Guest.
> 
> Signed-off-by: Anup Patel <[email-masked]>
> Signed-off-by: Pranavkumar Sawargaonkar <[email-masked]>
> ---
>  arch/arm/include/asm/kvm_host.h   |    5 +++
>  arch/arm/include/asm/kvm_psci.h   |    1 +
>  arch/arm/kvm/psci.c               |   88 +++++++++++++++++++++++++++++++++++--
>  arch/arm/kvm/reset.c              |    4 ++
>  arch/arm64/include/asm/kvm_host.h |    5 +++
>  arch/arm64/include/asm/kvm_psci.h |    1 +
>  arch/arm64/kvm/reset.c            |    4 ++
>  7 files changed, 104 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 193ceaf..2cc36a6 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -131,6 +131,11 @@ struct kvm_vcpu_arch {
>  	/* Don't run the guest on this vcpu */
>  	bool pause;
>  
> +	/* PSCI suspend state */
> +	bool suspend;
> +	u32 suspend_entry;
> +	u32 suspend_context_id;
> +
>  	/* IO related fields */
>  	struct kvm_decode mmio_decode;
>  
> diff --git a/arch/arm/include/asm/kvm_psci.h b/arch/arm/include/asm/kvm_psci.h
> index 6bda945..6a05ada 100644
> --- a/arch/arm/include/asm/kvm_psci.h
> +++ b/arch/arm/include/asm/kvm_psci.h
> @@ -22,6 +22,7 @@
>  #define KVM_ARM_PSCI_0_2	2
>  
>  int kvm_psci_version(struct kvm_vcpu *vcpu);
> +void kvm_psci_reset(struct kvm_vcpu *vcpu);
>  int kvm_psci_call(struct kvm_vcpu *vcpu);
>  
>  #endif /* __ARM_KVM_PSCI_H__ */
> diff --git a/arch/arm/kvm/psci.c b/arch/arm/kvm/psci.c
> index 675866e..482b0f6 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/smp.h>
>  #include <linux/kvm_host.h>
>  #include <linux/wait.h>
>  
> @@ -27,9 +28,81 @@
>   * as described in ARM document number ARM DEN 0022A.
>   */
>  
> +struct psci_suspend_info {
> +	struct kvm_vcpu *vcpu;
> +	unsigned long saved_entry;
> +	unsigned long saved_context_id;
> +};
> +
> +static void psci_do_suspend(void *context)
> +{
> +	struct psci_suspend_info *sinfo = context;
> +
> +	sinfo->vcpu->arch.pause = true;
> +	sinfo->vcpu->arch.suspend = true;
> +	sinfo->vcpu->arch.suspend_entry = sinfo->saved_entry;
> +	sinfo->vcpu->arch.suspend_context_id = sinfo->saved_context_id;

I don't really understand this, why are you not just setting pause =
true and modifying the registers as per the reentry rules in the spec?

Doesn't seem like this patch ever reads any of these values back?

> +}
> +
> +static unsigned long kvm_psci_vcpu_suspend(struct kvm_vcpu *vcpu)
> +{
> +	int i;
> +	unsigned long mpidr;
> +	unsigned long target_affinity;
> +	unsigned long target_affinity_mask;
> +	unsigned long lowest_affinity_level;
> +	struct kvm *kvm = vcpu->kvm;
> +	struct kvm_vcpu *tmp;
> +	struct psci_suspend_info sinfo;
> +
> +	target_affinity = kvm_vcpu_get_mpidr(vcpu);
> +	lowest_affinity_level = (*vcpu_reg(vcpu, 1) >> 24) & 0x3;
> +
> +	/* Determine target affinity mask */
> +	target_affinity_mask = MPIDR_HWID_BITMASK;
> +	switch (lowest_affinity_level) {
> +	case 0: /* All affinity levels are valid */
> +		target_affinity_mask &= ~0x0UL;
> +		break;
> +	case 1: /* Aff0 ignored */
> +		target_affinity_mask &= ~0xFFUL;
> +		break;
> +	case 2: /* Aff0 and Aff1 ignored */
> +		target_affinity_mask &= ~0xFFFFUL;
> +		break;
> +	case 3: /* Aff0, Aff1, and Aff2 ignored */
> +		target_affinity_mask &= ~0xFFFFFFUL;
> +		break;
> +	default:
> +		return KVM_PSCI_RET_INVAL;
> +	};

I feel like I've read this code before, can you factor it out?

> +
> +	/* Ignore other bits of target affinity */
> +	target_affinity &= target_affinity_mask;
> +
> +	/* Prepare suspend info */
> +	sinfo.vcpu = NULL;
> +	sinfo.saved_entry = *vcpu_reg(vcpu, 2);
> +	sinfo.saved_context_id = *vcpu_reg(vcpu, 3);
> +
> +	/* Suspend all VCPUs within target affinity */
> +	kvm_for_each_vcpu(i, tmp, kvm) {
> +		mpidr = kvm_vcpu_get_mpidr(tmp);
> +		if (((mpidr & target_affinity_mask) == target_affinity) &&
> +		    !tmp->arch.suspend) {
> +			sinfo.vcpu = tmp;
> +			smp_call_function_single(tmp->cpu,
> +						 psci_do_suspend, &sinfo, 1);

Hmmm, are you sure this is correct?  How does that correspond to the
PSCI docs saying

"It is only possible to call CPU_SUSPEND from the current core. That is,
it is not possible to request suspension of another core."

I would think this means, if all other cores in the specified affinity
level are already suspended, allow suspending the entire
cluster/group/..., but I may be wrong.

My comments above notwithstanding, this also feels racy.  What happens
if two virtual cores within the same affinity level calls CPU_SUSPEND at
the same time?

Also, there doesn't seem to be any handling of the StateType requested
by the caller, the reentry behavior is very different depending on the
state you enter, unless you always treat the request as a suspend
(clause 3 under Section 5.4.2 in the PSCI spec), in that case that
deserves a comment.

> +		}
> +	}
> +
> +	return KVM_PSCI_RET_SUCCESS;
> +}
> +
>  static void kvm_psci_vcpu_off(struct kvm_vcpu *vcpu)
>  {
>  	vcpu->arch.pause = true;
> +	vcpu->arch.suspend = false;
>  }
>  
>  static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu,
> @@ -179,6 +252,10 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
>  		 */
>  		val = 2;
>  		break;
> +	case KVM_PSCI_0_2_FN_CPU_SUSPEND:
> +	case KVM_PSCI_0_2_FN64_CPU_SUSPEND:
> +		val = kvm_psci_vcpu_suspend(vcpu);
> +		break;
>  	case KVM_PSCI_0_2_FN_CPU_OFF:
>  		kvm_psci_vcpu_off(vcpu);
>  		val = KVM_PSCI_RET_SUCCESS;
> @@ -216,10 +293,6 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
>  		val = KVM_PSCI_RET_SUCCESS;
>  		ret = 0;
>  		break;
> -	case KVM_PSCI_0_2_FN_CPU_SUSPEND:
> -	case KVM_PSCI_0_2_FN64_CPU_SUSPEND:
> -		val = KVM_PSCI_RET_NI;
> -		break;
>  	default:
>  		return -EINVAL;
>  	}
> @@ -253,6 +326,13 @@ static int kvm_psci_0_1_call(struct kvm_vcpu *vcpu)
>  	return 1;
>  }
>  
> +void kvm_psci_reset(struct kvm_vcpu *vcpu)
> +{
> +	vcpu->arch.suspend = false;
> +	vcpu->arch.suspend_entry = 0;
> +	vcpu->arch.suspend_context_id = 0;
> +}
> +
>  /**
>   * kvm_psci_call - handle PSCI call if r0 value is in range
>   * @vcpu: Pointer to the VCPU struct
> diff --git a/arch/arm/kvm/reset.c b/arch/arm/kvm/reset.c
> index f558c07..220c892 100644
> --- a/arch/arm/kvm/reset.c
> +++ b/arch/arm/kvm/reset.c
> @@ -26,6 +26,7 @@
>  #include <asm/cputype.h>
>  #include <asm/kvm_arm.h>
>  #include <asm/kvm_coproc.h>
> +#include <asm/kvm_psci.h>
>  
>  #include <kvm/arm_arch_timer.h>
>  
> @@ -79,5 +80,8 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
>  	/* Reset arch_timer context */
>  	kvm_timer_vcpu_reset(vcpu, cpu_vtimer_irq);
>  
> +	/* Reset PSCI state */
> +	kvm_psci_reset(vcpu);
> +
>  	return 0;
>  }
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 92242ce..b2c97dc 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -119,6 +119,11 @@ struct kvm_vcpu_arch {
>  	/* Don't run the guest */
>  	bool pause;
>  
> +	/* PSCI suspend state */
> +	bool suspend;
> +	u64 suspend_entry;
> +	u64 suspend_context_id;
> +
>  	/* IO related fields */
>  	struct kvm_decode mmio_decode;
>  
> diff --git a/arch/arm64/include/asm/kvm_psci.h b/arch/arm64/include/asm/kvm_psci.h
> index bc39e55..4da675d 100644
> --- a/arch/arm64/include/asm/kvm_psci.h
> +++ b/arch/arm64/include/asm/kvm_psci.h
> @@ -22,6 +22,7 @@
>  #define KVM_ARM_PSCI_0_2	2
>  
>  int kvm_psci_version(struct kvm_vcpu *vcpu);
> +void kvm_psci_reset(struct kvm_vcpu *vcpu);
>  int kvm_psci_call(struct kvm_vcpu *vcpu);
>  
>  #endif /* __ARM64_KVM_PSCI_H__ */
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index 70a7816..aca9f65 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -29,6 +29,7 @@
>  #include <asm/ptrace.h>
>  #include <asm/kvm_arm.h>
>  #include <asm/kvm_coproc.h>
> +#include <asm/kvm_psci.h>
>  
>  /*
>   * ARMv8 Reset Values
> @@ -108,5 +109,8 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
>  	/* Reset timer */
>  	kvm_timer_vcpu_reset(vcpu, cpu_vtimer_irq);
>  
> +	/* Reset PSCI state */
> +	kvm_psci_reset(vcpu);
> +
>  	return 0;
>  }
> -- 
> 1.7.9.5
> 

Thanks,
-- 
Christoffer