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

From: Paolo Bonzini <pbonzini@redhat.com>
To: David Gibson <david@gibson.dropbear.id.au>
Cc: kvm@vger.kernel.org, Alexey Kardashevskiy <aik@ozlabs.ru>,
	linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org,
	Alexander Graf <agraf@suse.de>, Paul Mackerras <paulus@samba.org>,
	Scott Wood <scottwood@freescale.com>,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling
Date: Mon, 27 May 2013 12:23:20 +0200	[thread overview]
Message-ID: <51A33418.40909@redhat.com> (raw)
In-Reply-To: <20130525024524.GA6112@boomeroo.fritz.box>

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.

KVM_CREATE_SPAPR_TCE could stay for backwards-compatibility, or you
could just use a new capability and drop the old ioctl.  I'm not sure
whether you're already considering the ABI to be stable for kvmppc.

Paolo