Re: [PATCH guest kernel] vfio/powerpc/spapr_tce: Enforce IOMMU type compatibility check

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 25/03/17 07:29, Alex Williamson wrote:
> On Fri, 24 Mar 2017 17:44:06 +1100
> Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
> 
>> The existing SPAPR TCE driver advertises both VFIO_SPAPR_TCE_IOMMU and
>> VFIO_SPAPR_TCE_v2_IOMMU types to the userspace and the userspace usually
>> picks the v2.
>>
>> Normally the userspace would create a container, attach an IOMMU group
>> to it and only then set the IOMMU type (which would normally be v2).
>>
>> However a specific IOMMU group may not support v2, in other words
>> it may not implement set_window/unset_window/take_ownership/
>> release_ownership and such a group should not be attached to
>> a v2 container.
>>
>> This adds extra checks that a new group can do what the selected IOMMU
>> type suggests. The userspace can then test the return value from
>> ioctl(VFIO_SET_IOMMU, VFIO_SPAPR_TCE_v2_IOMMU) and try
>> VFIO_SPAPR_TCE_IOMMU.
>>
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>> ---
>>
>> This is one of the patches needed to do nested VFIO - for either
>> second level guest or DPDK running in a guest.
>> ---
>>  drivers/vfio/vfio_iommu_spapr_tce.c | 8 ++++++++
>>  1 file changed, 8 insertions(+)
> 
> I'm not sure I understand why you're labeling this "guest kernel", is a


That is my script :)

> VM the only case where we can have combinations that only a subset of
> the groups might support v2?  

powernv (non-virtualized, and it runs HV KVM) host provides v2-capable
groups, they all the same, and a pseries host (which normally runs as a
guest but it can do nested KVM as well - it is called PR KVM) can do only
v1 (after this patch, without it - no vfio at all).

> What terrible things happen when such a
> combination is created?

There is no mixture at the moment, I just needed a way to tell userspace
that a group cannot do v2.

> The fix itself seems sane, but I'm trying to
> figure out whether it should be marked for stable, should go in for
> v4.11, or be queued for v4.12.  Thanks,

No need for stable.


> 
> Alex
> 
>> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
>> index cf3de91fbfe7..a7d811524092 100644
>> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
>> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
>> @@ -1335,8 +1335,16 @@ static int tce_iommu_attach_group(void *iommu_data,
>>  
>>  	if (!table_group->ops || !table_group->ops->take_ownership ||
>>  			!table_group->ops->release_ownership) {
>> +		if (container->v2) {
>> +			ret = -EPERM;
>> +			goto unlock_exit;
>> +		}
>>  		ret = tce_iommu_take_ownership(container, table_group);
>>  	} else {
>> +		if (!container->v2) {
>> +			ret = -EPERM;
>> +			goto unlock_exit;
>> +		}
>>  		ret = tce_iommu_take_ownership_ddw(container, table_group);
>>  		if (!tce_groups_attached(container) && !container->tables[0])
>>  			container->def_window_pending = true;
> 


-- 
Alexey