Re: [PATCH kernel] vfio/spapr_tce: Skip unsetting already unset table

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 13/02/2019 07:52, Alex Williamson wrote:
> On Mon, 11 Feb 2019 18:49:17 +1100
> Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
> 
>> VFIO TCE IOMMU v2 owns IOMMU tables so when detach a IOMMU group from
>> a container, we need to unset those from a group so we call unset_window()
>> so do we unconditionally. We also unset tables when removing a DMA window
> 
> Patch looks ok, but this first sentence trails off into a bit of a word
> salad.  Care to refine a bit?  Thanks,

Fair comment, sorry for the salad. How about this?

===
VFIO TCE IOMMU v2 owns IOMMU tables. When we detach an IOMMU group from
a container, we need to unset these tables from the group which we do by
calling unset_window(). We also unset tables when removing a DMA window
via the VFIO_IOMMU_SPAPR_TCE_REMOVE ioctl.
===


> 
> Alex
> 
>> via the VFIO_IOMMU_SPAPR_TCE_REMOVE ioctl.
>>
>> The window removal checks if the table actually exists (hidden inside
>> tce_iommu_find_table()) but the group detaching does not so the user
>> may see duplicating messages:
>> pci 0009:03     : [PE# fd] Removing DMA window #0
>> pci 0009:03     : [PE# fd] Removing DMA window #1
>> pci 0009:03     : [PE# fd] Removing DMA window #0
>> pci 0009:03     : [PE# fd] Removing DMA window #1
>>
>> At the moment this is not a problem as the second invocation
>> of unset_window() writes zeroes to the HW registers again and exits early
>> as there is no table.
>>
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>> ---
>>
>> When doing VFIO PCI hot unplug, first we remove the DMA window and
>> set container->tables[num] - this is a first couple of messages.
>> Then we detach the group and then we see another couple of the same
>> messages which confused myself.
>> ---
>>  drivers/vfio/vfio_iommu_spapr_tce.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
>> index c424913..8dbb270 100644
>> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
>> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
>> @@ -1235,7 +1235,8 @@ static void tce_iommu_release_ownership_ddw(struct tce_container *container,
>>  	}
>>  
>>  	for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i)
>> -		table_group->ops->unset_window(table_group, i);
>> +		if (container->tables[i])
>> +			table_group->ops->unset_window(table_group, i);
>>  
>>  	table_group->ops->release_ownership(table_group);
>>  }
> 

-- 
Alexey