Subject: [PATCH 2/2] ARM/ARM64: KVM: Forward PSCI SYSTEM_OFF and SYSTEM_RESET to user space

From: [email-masked] (Christoffer Dall)
Date: Mon, 9 Dec 2013 14:51:56 -0800

On Mon, Nov 25, 2013 at 09:19:59PM +0530, Anup Patel wrote:
> The PSCI SYSTEM_OFF and SYSTEM_RESET functions are system-level
> functions hence cannot be fully emulated by the in-kernel PSCI
> emulation code.
> 
> To tackle this, we forward PSCI SYSTEM_OFF and SYSTEM_RESET function
> calls from guest to user space (i.e. QEMU or KVMTOOL) via KVM run
> structure using KVM_EXIT_SHUTDOWN and KVM_EXIT_RESET exit reasons.
> 
> Signed-off-by: Anup Patel <[email-masked]>
> Signed-off-by: Pranavkumar Sawargaonkar <[email-masked]>
> ---
>  arch/arm/include/asm/kvm_psci.h   |    2 +-
>  arch/arm/include/uapi/asm/kvm.h   |    2 ++
>  arch/arm/kvm/handle_exit.c        |    7 ++++++-
>  arch/arm/kvm/psci.c               |   38 +++++++++++++++++++++++++++++--------
>  arch/arm64/include/asm/kvm_psci.h |    2 +-
>  arch/arm64/include/uapi/asm/kvm.h |    2 ++
>  arch/arm64/kvm/handle_exit.c      |   10 ++++++----
>  7 files changed, 48 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_psci.h b/arch/arm/include/asm/kvm_psci.h
> index 9a83d98..992d7f1 100644
> --- a/arch/arm/include/asm/kvm_psci.h
> +++ b/arch/arm/include/asm/kvm_psci.h
> @@ -18,6 +18,6 @@
>  #ifndef __ARM_KVM_PSCI_H__
>  #define __ARM_KVM_PSCI_H__
>  
> -bool kvm_psci_call(struct kvm_vcpu *vcpu);
> +int kvm_psci_call(struct kvm_vcpu *vcpu);
>  
>  #endif /* __ARM_KVM_PSCI_H__ */
> diff --git a/arch/arm/include/uapi/asm/kvm.h b/arch/arm/include/uapi/asm/kvm.h
> index c498b60..f4de20c 100644
> --- a/arch/arm/include/uapi/asm/kvm.h
> +++ b/arch/arm/include/uapi/asm/kvm.h
> @@ -172,6 +172,8 @@ struct kvm_arch_memory_slot {
>  #define KVM_PSCI_FN_CPU_OFF		KVM_PSCI_FN(1)
>  #define KVM_PSCI_FN_CPU_ON		KVM_PSCI_FN(2)
>  #define KVM_PSCI_FN_MIGRATE		KVM_PSCI_FN(3)
> +#define KVM_PSCI_FN_SYSTEM_OFF		KVM_PSCI_FN(4)
> +#define KVM_PSCI_FN_SYSTEM_RESET	KVM_PSCI_FN(5)
>  
>  #define KVM_PSCI_RET_SUCCESS		0
>  #define KVM_PSCI_RET_NI			((unsigned long)-1)
> diff --git a/arch/arm/kvm/handle_exit.c b/arch/arm/kvm/handle_exit.c
> index a920790..c96c7e8 100644
> --- a/arch/arm/kvm/handle_exit.c
> +++ b/arch/arm/kvm/handle_exit.c
> @@ -40,11 +40,16 @@ static int handle_svc_hyp(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  
>  static int handle_hvc(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  {
> +	int ret;
> +
>  	trace_kvm_hvc(*vcpu_pc(vcpu), *vcpu_reg(vcpu, 0),
>  		      kvm_vcpu_hvc_get_imm(vcpu));
>  
> -	if (kvm_psci_call(vcpu))
> +	ret = kvm_psci_call(vcpu);
> +	if (ret == 0)
>  		return 1;
> +	else if (ret > 0)
> +		return 0;
>  
>  	kvm_inject_undefined(vcpu);
>  	return 1;
> diff --git a/arch/arm/kvm/psci.c b/arch/arm/kvm/psci.c
> index 0881bf1..c8d3fcd 100644
> --- a/arch/arm/kvm/psci.c
> +++ b/arch/arm/kvm/psci.c
> @@ -84,18 +84,31 @@ static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu)
>  	return KVM_PSCI_RET_SUCCESS;
>  }
>  
> +static void kvm_psci_system_off(struct kvm_vcpu *vcpu)
> +{
> +	vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
> +}
> +
> +static void kvm_psci_system_reset(struct kvm_vcpu *vcpu)
> +{
> +	vcpu->run->exit_reason = KVM_EXIT_RESET;
> +}
> +
>  /**
>   * kvm_psci_call - handle PSCI call if r0 value is in range
>   * @vcpu: Pointer to the VCPU struct
>   *
>   * Handle PSCI calls from guests through traps from HVC instructions.
> - * The calling convention is similar to SMC calls to the secure world where
> - * the function number is placed in r0 and this function returns true if the
> - * function number specified in r0 is withing the PSCI range, and false
> - * otherwise.
> + * The calling convention is similar to SMC calls to the secure world
> + * where the function number is placed in r0 and function number
> + * specified in r0 is withing the PSCI range.
> + *
> + * This function returns: 0 (success), > 0 (success but exit to user
> + * space), and < 0 (failure)

Hmmm, I think this is a bit confusing because it essentially does the
reverse of all the other kvm internal return convention.  Wouldn't it
make more sense to have 0 (success, but exit to user space), 1 (success,
resume VM), and < 0 (failure).

Also note that you are general-casing all error codes that may happen to
mean that it did not match the PSCI function to anything well-known.
In this case, that's sort of ok, because we don't expect the PSCI code
to randomly fail (if it does, it reports it to the caller in the return
register), but not fail, as in, I'm out of memory or anything like that.
But I think you can clarify this in the comment, by saying something
like:

Errors:
 -EINVAL: Unrecognized PSCI function

in the comment for the function.

>   */
> -bool kvm_psci_call(struct kvm_vcpu *vcpu)
> +int kvm_psci_call(struct kvm_vcpu *vcpu)
>  {
> +	int ret = 0;
>  	unsigned long psci_fn = *vcpu_reg(vcpu, 0) & ~((u32) 0);
>  	unsigned long val;
>  
> @@ -111,11 +124,20 @@ bool kvm_psci_call(struct kvm_vcpu *vcpu)
>  	case KVM_PSCI_FN_MIGRATE:
>  		val = KVM_PSCI_RET_NI;
>  		break;
> -
> +	case KVM_PSCI_FN_SYSTEM_OFF:
> +		kvm_psci_system_off(vcpu);
> +		val = KVM_PSCI_RET_SUCCESS;
> +		ret = 1;
> +		break;
> +	case KVM_PSCI_FN_SYSTEM_RESET:
> +		kvm_psci_system_reset(vcpu);
> +		val = KVM_PSCI_RET_SUCCESS;
> +		ret = 1;
> +		break;
>  	default:
> -		return false;
> +		return -EINVAL;
>  	}
>  
>  	*vcpu_reg(vcpu, 0) = val;
> -	return true;
> +	return ret;
>  }
> diff --git a/arch/arm64/include/asm/kvm_psci.h b/arch/arm64/include/asm/kvm_psci.h
> index e301a48..9bd0ee8 100644
> --- a/arch/arm64/include/asm/kvm_psci.h
> +++ b/arch/arm64/include/asm/kvm_psci.h
> @@ -18,6 +18,6 @@
>  #ifndef __ARM64_KVM_PSCI_H__
>  #define __ARM64_KVM_PSCI_H__
>  
> -bool kvm_psci_call(struct kvm_vcpu *vcpu);
> +int kvm_psci_call(struct kvm_vcpu *vcpu);
>  
>  #endif /* __ARM64_KVM_PSCI_H__ */
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index d9f026b..f678902 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -158,6 +158,8 @@ struct kvm_arch_memory_slot {
>  #define KVM_PSCI_FN_CPU_OFF		KVM_PSCI_FN(1)
>  #define KVM_PSCI_FN_CPU_ON		KVM_PSCI_FN(2)
>  #define KVM_PSCI_FN_MIGRATE		KVM_PSCI_FN(3)
> +#define KVM_PSCI_FN_SYSTEM_OFF		KVM_PSCI_FN(4)
> +#define KVM_PSCI_FN_SYSTEM_RESET	KVM_PSCI_FN(5)
>  
>  #define KVM_PSCI_RET_SUCCESS		0
>  #define KVM_PSCI_RET_NI			((unsigned long)-1)
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 8da5606..a5b5b6a 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -30,8 +30,13 @@ typedef int (*exit_handle_fn)(struct kvm_vcpu *, struct kvm_run *);
>  
>  static int handle_hvc(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  {
> -	if (kvm_psci_call(vcpu))
> +	int ret;
> +
> +	ret = kvm_psci_call(vcpu);
> +	if (ret == 0)
>  		return 1;
> +	else if (ret > 0)
> +		return 0;
>  
>  	kvm_inject_undefined(vcpu);
>  	return 1;
> @@ -39,9 +44,6 @@ static int handle_hvc(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  
>  static int handle_smc(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  {
> -	if (kvm_psci_call(vcpu))
> -		return 1;
> -

Isn't this an unrelated change, which should go in a separate patch with
some justification text for the change?

>  	kvm_inject_undefined(vcpu);
>  	return 1;
>  }
> -- 
> 1.7.9.5
> 

Otherwise, it looks overall to go in the right direction.

-Christoffer