Re: [PATCH v3 1/4] kvmtool: ARM: Use KVM_ARM_PREFERRED_TARGET vm ioctl to determine target cpu

[Andre Przywara <andre.przywara@arm.com>]

Hi Anup,

On 08/09/14 09:17, Anup Patel wrote:
> Instead, of trying out each and every target type we should
> use KVM_ARM_PREFERRED_TARGET vm ioctl to determine target type
> for KVM ARM/ARM64.
> 
> If KVM_ARM_PREFERRED_TARGET vm ioctl fails then we fallback to
> old method of trying all known target types.
> 
> If KVM_ARM_PREFERRED_TARGET vm ioctl succeeds but the returned
> target type is not known to KVMTOOL then we forcefully init
> VCPU with target type returned by KVM_ARM_PREFERRED_TARGET vm ioctl.
> 
> Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
> Signed-off-by: Anup Patel <anup.patel@linaro.org>
> ---
>  tools/kvm/arm/kvm-cpu.c |   52 +++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 41 insertions(+), 11 deletions(-)
> 
> diff --git a/tools/kvm/arm/kvm-cpu.c b/tools/kvm/arm/kvm-cpu.c
> index aeaa4cf..ba7a762 100644
> --- a/tools/kvm/arm/kvm-cpu.c
> +++ b/tools/kvm/arm/kvm-cpu.c
> @@ -33,7 +33,8 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
>  	struct kvm_arm_target *target;
>  	struct kvm_cpu *vcpu;
>  	int coalesced_offset, mmap_size, err = -1;
> -	unsigned int i;
> +	unsigned int i, target_type;
> +	struct kvm_vcpu_init preferred_init;
>  	struct kvm_vcpu_init vcpu_init = {
>  		.features = ARM_VCPU_FEATURE_FLAGS(kvm, cpu_id)
>  	};
> @@ -55,19 +56,47 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
>  	if (vcpu->kvm_run == MAP_FAILED)
>  		die("unable to mmap vcpu fd");
>  
> -	/* Find an appropriate target CPU type. */
> -	for (i = 0; i < ARRAY_SIZE(kvm_arm_targets); ++i) {
> -		if (!kvm_arm_targets[i])
> -			continue;
> -		target = kvm_arm_targets[i];
> -		vcpu_init.target = target->id;
> -		err = ioctl(vcpu->vcpu_fd, KVM_ARM_VCPU_INIT, &vcpu_init);
> -		if (!err)
> -			break;
> +	/*
> +	 * If preferred target ioctl successful then use preferred target
> +	 * else try each and every target type.
> +	 */
> +	err = ioctl(kvm->vm_fd, KVM_ARM_PREFERRED_TARGET, &preferred_init);
> +	if (!err) {
> +		/* Match preferred target CPU type. */
> +		target = NULL;
> +		for (i = 0; i < ARRAY_SIZE(kvm_arm_targets); ++i) {
> +			if (!kvm_arm_targets[i])
> +				continue;
> +			if (kvm_arm_targets[i]->id == preferred_init.target) {
> +				target = kvm_arm_targets[i];
> +				target_type = kvm_arm_targets[i]->id;
> +				break;
> +			}
> +		}
> +		if (!target) {
> +			target = kvm_arm_targets[0];

I think you missed the part of the patch which adds the now magic zero
member of kvm_arm_targets[]. A simple static initializer should work.

> +			target_type = preferred_init.target;

Can't you move that out of the loop, in front of it actually? Then you
can get rid of the line above setting the target_type also, since you
always use the same value now, regardless whether you found that CPU in
the list or not.

> +		}
> +	} else {
> +		/* Find an appropriate target CPU type. */
> +		for (i = 0; i < ARRAY_SIZE(kvm_arm_targets); ++i) {
> +			if (!kvm_arm_targets[i])
> +				continue;
> +			target = kvm_arm_targets[i];
> +			target_type = target->id;
> +			vcpu_init.target = target_type;
> +			err = ioctl(vcpu->vcpu_fd, KVM_ARM_VCPU_INIT, &vcpu_init);
> +			if (!err)
> +				break;
> +		}
> +		if (err)
> +			die("Unable to find matching target");
>  	}
>  
> +	vcpu_init.target = target_type;
> +	err = ioctl(vcpu->vcpu_fd, KVM_ARM_VCPU_INIT, &vcpu_init);

You should do this only in the if-branch above, since you (try to) call
KVM_ARM_VCPU_INIT already in the else branch before. Otherwise in the
latter case you would do it twice.

Regards,
Andre.

>  	if (err || target->init(vcpu))
> -		die("Unable to initialise ARM vcpu");
> +		die("Unable to initialise vcpu");
>  
>  	coalesced_offset = ioctl(kvm->sys_fd, KVM_CHECK_EXTENSION,
>  				 KVM_CAP_COALESCED_MMIO);
> @@ -81,6 +110,7 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
>  	vcpu->cpu_type		= target->id;
>  	vcpu->cpu_compatible	= target->compatible;
>  	vcpu->is_running	= true;
> +
>  	return vcpu;
>  }
>  
>