Subject: Re: [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling

From: Alexey Kardashevskiy <[email-masked]>
Date: Tue, 28 May 2013 00:26:48 +1000

On 05/27/2013 08:23 PM, Paolo Bonzini wrote:
> Il 25/05/2013 04:45, David Gibson ha scritto:
>>>> +	case KVM_CREATE_SPAPR_TCE_IOMMU: {
>>>> +		struct kvm_create_spapr_tce_iommu create_tce_iommu;
>>>> +		struct kvm *kvm = filp->private_data;
>>>> +
>>>> +		r = -EFAULT;
>>>> +		if (copy_from_user(&create_tce_iommu, argp,
>>>> +				sizeof(create_tce_iommu)))
>>>> +			goto out;
>>>> +		r = kvm_vm_ioctl_create_spapr_tce_iommu(kvm,
>>>> &create_tce_iommu);
>>>> +		goto out;
>>>> +	}
> 
> Would it make sense to make this the only interface for creating TCEs?
> That is, pass both a window_size and an IOMMU group id (or e.g. -1 for
> no hardware IOMMU usage), and have a single ioctl for both cases?
> There's some duplicated code between kvm_vm_ioctl_create_spapr_tce and
> kvm_vm_ioctl_create_spapr_tce_iommu.

Just few bits. Is there really much sense in making one function from those
two? I tried, looked a bit messy.

> KVM_CREATE_SPAPR_TCE could stay for backwards-compatibility, or you
> could just use a new capability and drop the old ioctl.

The old capability+ioctl already exist for quite a while and few QEMU
versions supporting it were released so we do not want just drop it. So
then what is the benefit of having a new interface with support of both types?

>  I'm not sure
> whether you're already considering the ABI to be stable for kvmppc.

Is any bit of KVM using it? Cannot see from Documentation/ABI.

-- 
Alexey