Re: [PATCH v3 4/4] vfio/type1: Use iommu_aux_at(de)tach_group() APIs

Lu Baolu
2020-07-30T02:46:34Z

Hi Alex,

On 7/30/20 4:32 AM, Alex Williamson wrote:
> On Tue, 14 Jul 2020 13:57:03 +0800
> Lu Baolu <baolu.lu@linux.intel.com> wrote:
>
>> Replace iommu_aux_at(de)tach_device() with iommu_aux_at(de)tach_group().
>> It also saves the IOMMU_DEV_FEAT_AUX-capable physcail device in the
>> vfio_group data structure so that it could be reused in other places.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>> drivers/vfio/vfio_iommu_type1.c | 44 ++++++---------------------------
>> 1 file changed, 7 insertions(+), 37 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index 5e556ac9102a..f8812e68de77 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -100,6 +100,7 @@ struct vfio_dma {
>> struct vfio_group {
>> struct iommu_group *iommu_group;
>> struct list_head next;
>> + struct device *iommu_device;
>> bool mdev_group; /* An mdev group */
>> bool pinned_page_dirty_scope;
>> };
>> @@ -1627,45 +1628,13 @@ static struct device *vfio_mdev_get_iommu_device(struct device *dev)
>> return NULL;
>> }
>>
>> -static int vfio_mdev_attach_domain(struct device *dev, void *data)
>> -{
>> - struct iommu_domain *domain = data;
>> - struct device *iommu_device;
>> -
>> - iommu_device = vfio_mdev_get_iommu_device(dev);
>> - if (iommu_device) {
>> - if (iommu_dev_feature_enabled(iommu_device, IOMMU_DEV_FEAT_AUX))
>> - return iommu_aux_attach_device(domain, iommu_device);
>> - else
>> - return iommu_attach_device(domain, iommu_device);
>> - }
>> -
>> - return -EINVAL;
>> -}
>> -
>> -static int vfio_mdev_detach_domain(struct device *dev, void *data)
>> -{
>> - struct iommu_domain *domain = data;
>> - struct device *iommu_device;
>> -
>> - iommu_device = vfio_mdev_get_iommu_device(dev);
>> - if (iommu_device) {
>> - if (iommu_dev_feature_enabled(iommu_device, IOMMU_DEV_FEAT_AUX))
>> - iommu_aux_detach_device(domain, iommu_device);
>> - else
>> - iommu_detach_device(domain, iommu_device);
>> - }
>> -
>> - return 0;
>> -}
>> -
>> static int vfio_iommu_attach_group(struct vfio_domain *domain,
>> struct vfio_group *group)
>> {
>> if (group->mdev_group)
>> - return iommu_group_for_each_dev(group->iommu_group,
>> - domain->domain,
>> - vfio_mdev_attach_domain);
>> + return iommu_aux_attach_group(domain->domain,
>> + group->iommu_group,
>> + group->iommu_device);
>
> No, we previously iterated all devices in the group and used the aux
> interface only when we have an iommu_device supporting aux. If we
> simply assume an mdev group only uses an aux domain we break existing
> users, ex. SR-IOV VF backed mdevs. Thanks,

Oh, yes. Sorry! I didn't consider the physical device backed mdevs
cases.

Looked into this part of code, it seems that there's a lock issue here.
The group->mutex is held in iommu_group_for_each_dev() and will be
acquired again in iommu_attach_device().

How about making it like:

static int vfio_iommu_attach_group(struct vfio_domain *domain,
struct vfio_group *group)
{
if (group->mdev_group) {
struct device *iommu_device = group->iommu_device;

if (WARN_ON(!iommu_device))
return -EINVAL;

if (iommu_dev_feature_enabled(iommu_device,
IOMMU_DEV_FEAT_AUX))
return iommu_aux_attach_device(domain->domain,
iommu_device);
else
return iommu_attach_device(domain->domain,
iommu_device);
} else {
return iommu_attach_group(domain->domain,
group->iommu_group);
}
}

The caller (vfio_iommu_type1_attach_group) has guaranteed that all mdevs
in an iommu group should be derived from a same physical device.

Any thoughts?

>
> Alex

Best regards,
baolu

>
>
>> else
>> return iommu_attach_group(domain->domain, group->iommu_group);
>> }
>> @@ -1674,8 +1643,8 @@ static void vfio_iommu_detach_group(struct vfio_domain *domain,
>> struct vfio_group *group)
>> {
>> if (group->mdev_group)
>> - iommu_group_for_each_dev(group->iommu_group, domain->domain,
>> - vfio_mdev_detach_domain);
>> + iommu_aux_detach_group(domain->domain, group->iommu_group,
>> + group->iommu_device);
>> else
>> iommu_detach_group(domain->domain, group->iommu_group);
>> }
>> @@ -2007,6 +1976,7 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
>> return 0;
>> }
>>
>> + group->iommu_device = iommu_device;
>> bus = iommu_device->bus;
>> }
>>