Re: [PATCH 1/5] kvmtool: ARM: Use KVM_ARM_PREFERRED_TARGET vm ioctl to determine target cpu

[Will Deacon <will.deacon@arm.com>]

On Tue, Aug 05, 2014 at 09:49:55AM +0100, 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.
> 
> We bail-out target type returned by KVM_ARM_PREFERRED_TARGET vm ioctl
> is not known to kvmtool.

-ENOPARSE

> Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
> Signed-off-by: Anup Patel <anup.patel@linaro.org>
> ---
>  tools/kvm/arm/kvm-cpu.c |   21 ++++++++++++++++-----
>  1 file changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/kvm/arm/kvm-cpu.c b/tools/kvm/arm/kvm-cpu.c
> index aeaa4cf..7478f8f 100644
> --- a/tools/kvm/arm/kvm-cpu.c
> +++ b/tools/kvm/arm/kvm-cpu.c
> @@ -34,6 +34,7 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
>  	struct kvm_cpu *vcpu;
>  	int coalesced_offset, mmap_size, err = -1;
>  	unsigned int i;
> +	struct kvm_vcpu_init preferred_init;
>  	struct kvm_vcpu_init vcpu_init = {
>  		.features = ARM_VCPU_FEATURE_FLAGS(kvm, cpu_id)
>  	};
> @@ -46,6 +47,10 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
>  	if (vcpu->vcpu_fd < 0)
>  		die_perror("KVM_CREATE_VCPU ioctl");
>  
> +	err = ioctl(kvm->vm_fd, KVM_ARM_PREFERRED_TARGET, &preferred_init);
> +	if (err < 0)
> +		die_perror("KVM_ARM_PREFERRED_TARGET ioctl");

Is this ioctl always available? If not, I don't like dying here as that
could cause a regression under older hosts.

Will