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

From: Alexey Kardashevskiy <[email-masked]>
Date: Mon, 27 May 2013 12:44:24 +1000

On 05/25/2013 12:45 PM, David Gibson wrote:
> On Wed, May 22, 2013 at 04:06:57PM -0500, Scott Wood wrote:
>> On 05/20/2013 10:06:46 PM, Alexey Kardashevskiy wrote:
>>> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
>>> index 8465c2a..da6bf61 100644
>>> --- a/arch/powerpc/kvm/powerpc.c
>>> @@ -396,6 +396,7 @@ int kvm_dev_ioctl_check_extension(long ext)
>>> +++ b/arch/powerpc/kvm/powerpc.c
>>> 		break;
>>> #endif
>>> 	case KVM_CAP_SPAPR_MULTITCE:
>>> +	case KVM_CAP_SPAPR_TCE_IOMMU:
>>> 		r = 1;
>>> 		break;
>>> 	default:
>>
>> Don't advertise SPAPR capabilities if it's not book3s -- and
>> probably there's some additional limitation that would be
>> appropriate.
> 
> So, in the case of MULTITCE, that's not quite right.  PR KVM can
> emulate a PAPR system on a BookE machine, and there's no reason not to
> allow TCE acceleration as well.  We can't make it dependent on PAPR
> mode being selected, because that's enabled per-vcpu, whereas these
> capabilities are queried on the VM before the vcpus are created.
> 
> CAP_SPAPR_TCE_IOMMU should be dependent on the presence of suitable
> host side hardware (i.e. a PAPR style IOMMU), though.

The capability says that the ioctl is supported. If there is no IOMMU group
registered, than it will fail with a reasonable error and nobody gets hurt.
What is the problem?

>>
>>> @@ -1025,6 +1026,17 @@ long kvm_arch_vm_ioctl(struct file *filp,
>>> 		r = kvm_vm_ioctl_create_spapr_tce(kvm, &create_tce);
>>> 		goto out;
>>> 	}
>>> +	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;
>>> +	}
>>> #endif /* CONFIG_PPC_BOOK3S_64 */
>>>
>>> #ifdef CONFIG_KVM_BOOK3S_64_HV
>>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>>> index 5a2afda..450c82a 100644
>>> --- a/include/uapi/linux/kvm.h
>>> +++ b/include/uapi/linux/kvm.h
>>> @@ -667,6 +667,7 @@ struct kvm_ppc_smmu_info {
>>> #define KVM_CAP_PPC_RTAS 91
>>> #define KVM_CAP_IRQ_XICS 92
>>> #define KVM_CAP_SPAPR_MULTITCE (0x110000 + 89)
>>> +#define KVM_CAP_SPAPR_TCE_IOMMU (0x110000 + 90)
>>
>> Hmm...
> 
> Ah, yeah, that needs to be fixed.  Those were interim numbers so that
> we didn't have to keep changing our internal trees as new upstream
> ioctls got added to the list.  We need to get a proper number for the
> merge, though.
>
>>> @@ -939,6 +940,9 @@ struct kvm_s390_ucas_mapping {
>>> #define KVM_GET_DEVICE_ATTR	  _IOW(KVMIO,  0xe2, struct
>>> kvm_device_attr)
>>> #define KVM_HAS_DEVICE_ATTR	  _IOW(KVMIO,  0xe3, struct
>>> kvm_device_attr)
>>>
>>> +/* ioctl for SPAPR TCE IOMMU */
>>> +#define KVM_CREATE_SPAPR_TCE_IOMMU _IOW(KVMIO,  0xe4, struct
>>> kvm_create_spapr_tce_iommu)
>>
>> Shouldn't this go under the vm ioctl section?

The KVM_CREATE_SPAPR_TCE_IOMMU ioctl (the version for emulated devices) is
in this section so I decided to keep them together. Wrong?

-- 
Alexey