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

[Anup Patel <anup.patel@linaro.org>]

On 6 August 2014 18:18, Will Deacon <will.deacon@arm.com> wrote:
> 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

OK, I will fix the wordings here.

>
>> 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.

The KVM_ARM_PREFERRED_TARGET ioctl is available from 3.13 onwards.

I think we should first try KVM_ARM_PREFERRED_TARGET. If it fails then
we should fallback to old method of trying each and every target type.
What say?

--
Anup

>
> Will