Re: [PATCH 4/4] vfio: Allow type-1 IOMMU instantiation with a virtio-iommu

[Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>]

On 14/02/18 15:26, Alex Williamson wrote:
> On Wed, 14 Feb 2018 14:53:40 +0000
> Jean-Philippe Brucker <jean-philippe.brucker-5wv7dgnIgG8@public.gmane.org> wrote:
> 
>> When enabling both VFIO and VIRTIO_IOMMU modules, automatically select
>> VFIO_IOMMU_TYPE1 as well.
>>
>> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker-5wv7dgnIgG8@public.gmane.org>
>> ---
>>   drivers/vfio/Kconfig | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/vfio/Kconfig b/drivers/vfio/Kconfig
>> index c84333eb5eb5..65a1e691110c 100644
>> --- a/drivers/vfio/Kconfig
>> +++ b/drivers/vfio/Kconfig
>> @@ -21,7 +21,7 @@ config VFIO_VIRQFD
>>   menuconfig VFIO
>>   	tristate "VFIO Non-Privileged userspace driver framework"
>>   	depends on IOMMU_API
>> -	select VFIO_IOMMU_TYPE1 if (X86 || S390 || ARM_SMMU || ARM_SMMU_V3)
>> +	select VFIO_IOMMU_TYPE1 if (X86 || S390 || ARM_SMMU || ARM_SMMU_V3 || VIRTIO_IOMMU)
>>   	select ANON_INODES
>>   	help
>>   	  VFIO provides a framework for secure userspace device drivers.
> 
> Why are we basing this on specific IOMMU drivers in the first place?
> Only ARM is doing that.  Shouldn't IOMMU_API only be enabled for ARM
> targets that support it and therefore we can forget about the specific
> IOMMU drivers?  Thanks,

Makes sense - the majority of ARM systems (and mobile/embedded ARM64 
ones) making use of IOMMU_API won't actually support VFIO, but it can't 
hurt to allow them to select the type 1 driver regardless. Especially as 
multiplatform configs are liable to be pulling in the SMMU driver(s) anyway.

Robin.