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

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 13 Feb 2019 11:18:21 +1100
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> 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.
> ===


Applied to vfio next branch with updated commit log and David's R-b.
Thanks,

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);
> >>  }  
> >   
>