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From: Lu Baolu <baolu.lu@linux.intel.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: baolu.lu@linux.intel.com, Joerg Roedel <joro@8bytes.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Jean-Philippe Brucker <jean-philippe@linaro.org>,
	Cornelia Huck <cohuck@redhat.com>,
	Kevin Tian <kevin.tian@intel.com>,
	Ashok Raj <ashok.raj@intel.com>,
	Dave Jiang <dave.jiang@intel.com>, Liu Yi L <yi.l.liu@intel.com>,
	iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org
Subject: Re: [PATCH v3 4/4] vfio/type1: Use iommu_aux_at(de)tach_group() APIs
Date: Fri, 31 Jul 2020 09:37:52 +0800
Message-ID: <7caa6533-b980-8135-6dba-2aac5b0bb23f@linux.intel.com> (raw)
In-Reply-To: <20200730151703.5daf8ad4@x1.home>

Hi Alex,

On 7/31/20 5:17 AM, Alex Williamson wrote:
> On Thu, 30 Jul 2020 10:41:32 +0800
> Lu Baolu <baolu.lu@linux.intel.com> wrote:
> 
>> 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().
> 
> These are two different groups.  We walk the devices in the mdev's
> group with iommu_group_for_each_dev(), holding the mdev's group lock,
> but we call iommu_attach_device() with iommu_device, which results in
> acquiring the lock for the iommu_device's group.

You are right. Sorry for the noise. Please ignore it.

> 
>> 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.
> 
> Have we?

We have done this with below.

static int vfio_mdev_iommu_device(struct device *dev, void *data)
{
         struct device **old = data, *new;

         new = vfio_mdev_get_iommu_device(dev);
         if (!new || (*old && *old != new))
                 return -EINVAL;

         *old = new;

         return 0;
}

But I agree that as a generic iommu aux-domain api, we shouldn't put
this limited assumption in it.

> iommu_attach_device() will fail if the group is not
> singleton, but that's just encouraging us to use the _attach_group()
> interface where the _attach_device() interface is relegated to special
> cases.  Ideally we'd get out of those special cases and create an
> _attach_group() for aux that doesn't further promote these notions.

Yes. Fair enough.

> 
>> Any thoughts?
> 
> See my reply to Kevin, I'm thinking we need to provide a callback that
> can enlighten the IOMMU layer to be able to do _attach_group() with
> aux or separate IOMMU backed devices.

Thanks for the guide. I will check your reply.

Best regards,
baolu

  reply index

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-14  5:56 [PATCH v3 0/4] iommu aux-domain APIs extensions Lu Baolu
2020-07-14  5:57 ` [PATCH v3 1/4] iommu: Check IOMMU_DEV_FEAT_AUX feature in aux api's Lu Baolu
2020-07-29 20:03   ` Alex Williamson
2020-07-30  1:46     ` Lu Baolu
2020-07-14  5:57 ` [PATCH v3 2/4] iommu: Add iommu_aux_at(de)tach_group() Lu Baolu
2020-07-14 16:39   ` Jacob Pan
2020-07-15  0:47     ` Lu Baolu
2020-07-15 16:01       ` Jacob Pan
2020-07-16  1:07         ` Lu Baolu
2020-07-29 20:03           ` Alex Williamson
2020-07-29 23:34             ` Tian, Kevin
2020-07-30 19:46               ` Alex Williamson
2020-07-31  5:47                 ` Lu Baolu
2020-07-31 18:05                   ` Alex Williamson
2020-08-03  1:57                     ` Lu Baolu
2020-07-14  5:57 ` [PATCH v3 3/4] iommu: Add iommu_aux_get_domain_for_dev() Lu Baolu
2020-07-29 20:25   ` Alex Williamson
2020-07-29 23:49     ` Tian, Kevin
2020-07-30 20:17       ` Alex Williamson
2020-07-31  0:26         ` Tian, Kevin
2020-07-31  2:17         ` Tian, Kevin
2020-07-31  6:30     ` Lu Baolu
2020-07-31 18:14       ` Alex Williamson
2020-08-03  2:15         ` Lu Baolu
2020-07-14  5:57 ` [PATCH v3 4/4] vfio/type1: Use iommu_aux_at(de)tach_group() APIs Lu Baolu
2020-07-14  8:25   ` Christoph Hellwig
2020-07-14 16:29     ` Jacob Pan
2020-07-15  1:00       ` Lu Baolu
2020-07-15  1:23         ` Tian, Kevin
2020-07-29 20:32   ` Alex Williamson
2020-07-30  2:41     ` Lu Baolu
2020-07-30 21:17       ` Alex Williamson
2020-07-31  1:37         ` Lu Baolu [this message]
2020-07-30  9:36   ` Liu, Yi L
2020-07-31  1:39     ` Lu Baolu
2020-07-23 13:55 ` [PATCH v3 0/4] iommu aux-domain APIs extensions Lu Baolu

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