Re: [PATCH v2] vfio/mdev: Check globally for duplicate devices

[Alex Williamson]

On Thu, 17 May 2018 01:01:40 +0530
Kirti Wankhede  wrote:

> On 5/16/2018 8:53 PM, Alex Williamson wrote:
> > When we create an mdev device, we check for duplicates against the
> > parent device and return -EEXIST if found, but the mdev device
> > namespace is global since we'll link all devices from the bus.  We do
> > catch this later in sysfs_do_create_link_sd() to return -EEXIST, but
> > with it comes a kernel warning and stack trace for trying to create
> > duplicate sysfs links, which makes it an undesirable response.
> > 
> > Therefore we should really be looking for duplicates across all mdev
> > parent devices, or as implemented here, against our mdev device list.
> > 
> > Notably, mdev_parent.lock really only seems to be serializing device
> > creation and removal per parent.  I'm not sure if this is necessary,
> > mdev vendor drivers could easily provide this serialization if it
> > is required, but a side-effect of holding the mdev_list_lock to
> > protect the namespace is actually greater serialization across the
> > create and remove paths,  
> 
> Exactly for this reason more granular lock is used and that's the reason
> mdev_parent.lock was introduced. Consider the max supported config for
> vGPU: 8 GPUs in a system with 16 mdev devices on each GPUs, i.e. 128
> mdev devices need to be created in a system, and this count will
> increase in future, all mdev device creation/removal will get serialized
> with this change.
> I agree with your concern that if there are duplicates across parents,
> its not caught earlier.

Right, thus the concern, but how often are trying to simultaneously
create or remove all those mdev devices.  Anyway...
 
> > so mdev_parent.lock is removed.  If we can
> > show that vendor drivers handle the create/remove paths themselves,
> > perhaps we can refine the locking granularity.
> >   
> 
> Here lock is not for create/remove routines of vendor driver, its about
> mdev device creation and device registration, which is a common code
> path, and so is part of mdev core module.

Ok, if mdev_parent.lock was only to protect the per parent device
namespace and not meant as a serialization guarantee to the vendor
drivers, then we can fix the bug and improve the parallelism.

> > Reviewed-by: Cornelia Huck 
> > Signed-off-by: Alex Williamson 
> > ---
> > 
> > v2: Remove unnecessary ret init per Cornelia's review
> > 
> >  drivers/vfio/mdev/mdev_core.c|   77 
> > +-
> >  drivers/vfio/mdev/mdev_private.h |1 
> >  2 files changed, 19 insertions(+), 59 deletions(-)
> > 
> > diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> > index 126991046eb7..aaab3ef93e1c 100644
> > --- a/drivers/vfio/mdev/mdev_core.c
> > +++ b/drivers/vfio/mdev/mdev_core.c
> > @@ -66,34 +66,6 @@ uuid_le mdev_uuid(struct mdev_device *mdev)
> >  }
> >  EXPORT_SYMBOL(mdev_uuid);
> >  
> > -static int _find_mdev_device(struct device *dev, void *data)
> > -{
> > -   struct mdev_device *mdev;
> > -
> > -   if (!dev_is_mdev(dev))
> > -   return 0;
> > -
> > -   mdev = to_mdev_device(dev);
> > -
> > -   if (uuid_le_cmp(mdev->uuid, *(uuid_le *)data) == 0)
> > -   return 1;
> > -
> > -   return 0;
> > -}
> > -
> > -static bool mdev_device_exist(struct mdev_parent *parent, uuid_le uuid)
> > -{
> > -   struct device *dev;
> > -
> > -   dev = device_find_child(parent->dev, , _find_mdev_device);
> > -   if (dev) {
> > -   put_device(dev);
> > -   return true;
> > -   }
> > -
> > -   return false;
> > -}
> > -
> >  /* Should be called holding parent_list_lock */
> >  static struct mdev_parent *__find_parent_device(struct device *dev)
> >  {
> > @@ -221,7 +193,6 @@ int mdev_register_device(struct device *dev, const 
> > struct mdev_parent_ops *ops)
> > }
> >  
> > kref_init(>ref);
> > -   mutex_init(>lock);
> >  
> > parent->dev = dev;
> > parent->ops = ops;
> > @@ -304,7 +275,7 @@ static void mdev_device_release(struct device *dev)
> >  int mdev_device_create(struct kobject *kobj, struct device *dev, uuid_le 
> > uuid)
> >  {
> > int ret;
> > -   struct mdev_device *mdev;
> > +   struct mdev_device *mdev, *tmp;
> > struct mdev_parent *parent;
> > struct mdev_type *type = to_mdev_type(kobj);
> >  
> > @@ -312,12 +283,14 @@ int mdev_device_create(struct kobject *kobj, struct 
> > device *dev, uuid_le uuid)
> > if (!parent)
> > return -EINVAL;
> >  
> > -   mutex_lock(>lock);
> > +   mutex_lock(_list_lock);
> >  
> > /* Check for duplicate */
> > -   if (mdev_device_exist(parent, uuid)) {
> > -   ret = -EEXIST;
> > -   goto create_err;
> > +   list_for_each_entry(tmp, _list, next) {
> > +   if (!uuid_le_cmp(tmp->uuid, uuid)) {
> > +   ret = -EEXIST;
> > +   goto create_err;
> > +   }
> > }
> >  
> Is it possible to use mdev_list_lock for as 

Re: [PATCH v2] vfio/mdev: Check globally for duplicate devices

[Alex Williamson]

On Thu, 17 May 2018 01:01:40 +0530
Kirti Wankhede  wrote:

> On 5/16/2018 8:53 PM, Alex Williamson wrote:
> > When we create an mdev device, we check for duplicates against the
> > parent device and return -EEXIST if found, but the mdev device
> > namespace is global since we'll link all devices from the bus.  We do
> > catch this later in sysfs_do_create_link_sd() to return -EEXIST, but
> > with it comes a kernel warning and stack trace for trying to create
> > duplicate sysfs links, which makes it an undesirable response.
> > 
> > Therefore we should really be looking for duplicates across all mdev
> > parent devices, or as implemented here, against our mdev device list.
> > 
> > Notably, mdev_parent.lock really only seems to be serializing device
> > creation and removal per parent.  I'm not sure if this is necessary,
> > mdev vendor drivers could easily provide this serialization if it
> > is required, but a side-effect of holding the mdev_list_lock to
> > protect the namespace is actually greater serialization across the
> > create and remove paths,  
> 
> Exactly for this reason more granular lock is used and that's the reason
> mdev_parent.lock was introduced. Consider the max supported config for
> vGPU: 8 GPUs in a system with 16 mdev devices on each GPUs, i.e. 128
> mdev devices need to be created in a system, and this count will
> increase in future, all mdev device creation/removal will get serialized
> with this change.
> I agree with your concern that if there are duplicates across parents,
> its not caught earlier.

Right, thus the concern, but how often are trying to simultaneously
create or remove all those mdev devices.  Anyway...
 
> > so mdev_parent.lock is removed.  If we can
> > show that vendor drivers handle the create/remove paths themselves,
> > perhaps we can refine the locking granularity.
> >   
> 
> Here lock is not for create/remove routines of vendor driver, its about
> mdev device creation and device registration, which is a common code
> path, and so is part of mdev core module.

Ok, if mdev_parent.lock was only to protect the per parent device
namespace and not meant as a serialization guarantee to the vendor
drivers, then we can fix the bug and improve the parallelism.

> > Reviewed-by: Cornelia Huck 
> > Signed-off-by: Alex Williamson 
> > ---
> > 
> > v2: Remove unnecessary ret init per Cornelia's review
> > 
> >  drivers/vfio/mdev/mdev_core.c|   77 
> > +-
> >  drivers/vfio/mdev/mdev_private.h |1 
> >  2 files changed, 19 insertions(+), 59 deletions(-)
> > 
> > diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> > index 126991046eb7..aaab3ef93e1c 100644
> > --- a/drivers/vfio/mdev/mdev_core.c
> > +++ b/drivers/vfio/mdev/mdev_core.c
> > @@ -66,34 +66,6 @@ uuid_le mdev_uuid(struct mdev_device *mdev)
> >  }
> >  EXPORT_SYMBOL(mdev_uuid);
> >  
> > -static int _find_mdev_device(struct device *dev, void *data)
> > -{
> > -   struct mdev_device *mdev;
> > -
> > -   if (!dev_is_mdev(dev))
> > -   return 0;
> > -
> > -   mdev = to_mdev_device(dev);
> > -
> > -   if (uuid_le_cmp(mdev->uuid, *(uuid_le *)data) == 0)
> > -   return 1;
> > -
> > -   return 0;
> > -}
> > -
> > -static bool mdev_device_exist(struct mdev_parent *parent, uuid_le uuid)
> > -{
> > -   struct device *dev;
> > -
> > -   dev = device_find_child(parent->dev, , _find_mdev_device);
> > -   if (dev) {
> > -   put_device(dev);
> > -   return true;
> > -   }
> > -
> > -   return false;
> > -}
> > -
> >  /* Should be called holding parent_list_lock */
> >  static struct mdev_parent *__find_parent_device(struct device *dev)
> >  {
> > @@ -221,7 +193,6 @@ int mdev_register_device(struct device *dev, const 
> > struct mdev_parent_ops *ops)
> > }
> >  
> > kref_init(>ref);
> > -   mutex_init(>lock);
> >  
> > parent->dev = dev;
> > parent->ops = ops;
> > @@ -304,7 +275,7 @@ static void mdev_device_release(struct device *dev)
> >  int mdev_device_create(struct kobject *kobj, struct device *dev, uuid_le 
> > uuid)
> >  {
> > int ret;
> > -   struct mdev_device *mdev;
> > +   struct mdev_device *mdev, *tmp;
> > struct mdev_parent *parent;
> > struct mdev_type *type = to_mdev_type(kobj);
> >  
> > @@ -312,12 +283,14 @@ int mdev_device_create(struct kobject *kobj, struct 
> > device *dev, uuid_le uuid)
> > if (!parent)
> > return -EINVAL;
> >  
> > -   mutex_lock(>lock);
> > +   mutex_lock(_list_lock);
> >  
> > /* Check for duplicate */
> > -   if (mdev_device_exist(parent, uuid)) {
> > -   ret = -EEXIST;
> > -   goto create_err;
> > +   list_for_each_entry(tmp, _list, next) {
> > +   if (!uuid_le_cmp(tmp->uuid, uuid)) {
> > +   ret = -EEXIST;
> > +   goto create_err;
> > +   }
> > }
> >  
> Is it possible to use mdev_list_lock for as minimal portion as possible?
> By adding mdev device to mdev_list just 

Re: [PATCH v2] vfio/mdev: Check globally for duplicate devices

[Kirti Wankhede]

On 5/16/2018 8:53 PM, Alex Williamson wrote:
> When we create an mdev device, we check for duplicates against the
> parent device and return -EEXIST if found, but the mdev device
> namespace is global since we'll link all devices from the bus.  We do
> catch this later in sysfs_do_create_link_sd() to return -EEXIST, but
> with it comes a kernel warning and stack trace for trying to create
> duplicate sysfs links, which makes it an undesirable response.
> 
> Therefore we should really be looking for duplicates across all mdev
> parent devices, or as implemented here, against our mdev device list.
> 
> Notably, mdev_parent.lock really only seems to be serializing device
> creation and removal per parent.  I'm not sure if this is necessary,
> mdev vendor drivers could easily provide this serialization if it
> is required, but a side-effect of holding the mdev_list_lock to
> protect the namespace is actually greater serialization across the
> create and remove paths,

Exactly for this reason more granular lock is used and that's the reason
mdev_parent.lock was introduced. Consider the max supported config for
vGPU: 8 GPUs in a system with 16 mdev devices on each GPUs, i.e. 128
mdev devices need to be created in a system, and this count will
increase in future, all mdev device creation/removal will get serialized
with this change.
I agree with your concern that if there are duplicates across parents,
its not caught earlier.

> so mdev_parent.lock is removed.  If we can
> show that vendor drivers handle the create/remove paths themselves,
> perhaps we can refine the locking granularity.
> 

Here lock is not for create/remove routines of vendor driver, its about
mdev device creation and device registration, which is a common code
path, and so is part of mdev core module.


> Reviewed-by: Cornelia Huck 
> Signed-off-by: Alex Williamson 
> ---
> 
> v2: Remove unnecessary ret init per Cornelia's review
> 
>  drivers/vfio/mdev/mdev_core.c|   77 
> +-
>  drivers/vfio/mdev/mdev_private.h |1 
>  2 files changed, 19 insertions(+), 59 deletions(-)
> 
> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> index 126991046eb7..aaab3ef93e1c 100644
> --- a/drivers/vfio/mdev/mdev_core.c
> +++ b/drivers/vfio/mdev/mdev_core.c
> @@ -66,34 +66,6 @@ uuid_le mdev_uuid(struct mdev_device *mdev)
>  }
>  EXPORT_SYMBOL(mdev_uuid);
>  
> -static int _find_mdev_device(struct device *dev, void *data)
> -{
> - struct mdev_device *mdev;
> -
> - if (!dev_is_mdev(dev))
> - return 0;
> -
> - mdev = to_mdev_device(dev);
> -
> - if (uuid_le_cmp(mdev->uuid, *(uuid_le *)data) == 0)
> - return 1;
> -
> - return 0;
> -}
> -
> -static bool mdev_device_exist(struct mdev_parent *parent, uuid_le uuid)
> -{
> - struct device *dev;
> -
> - dev = device_find_child(parent->dev, , _find_mdev_device);
> - if (dev) {
> - put_device(dev);
> - return true;
> - }
> -
> - return false;
> -}
> -
>  /* Should be called holding parent_list_lock */
>  static struct mdev_parent *__find_parent_device(struct device *dev)
>  {
> @@ -221,7 +193,6 @@ int mdev_register_device(struct device *dev, const struct 
> mdev_parent_ops *ops)
>   }
>  
>   kref_init(>ref);
> - mutex_init(>lock);
>  
>   parent->dev = dev;
>   parent->ops = ops;
> @@ -304,7 +275,7 @@ static void mdev_device_release(struct device *dev)
>  int mdev_device_create(struct kobject *kobj, struct device *dev, uuid_le 
> uuid)
>  {
>   int ret;
> - struct mdev_device *mdev;
> + struct mdev_device *mdev, *tmp;
>   struct mdev_parent *parent;
>   struct mdev_type *type = to_mdev_type(kobj);
>  
> @@ -312,12 +283,14 @@ int mdev_device_create(struct kobject *kobj, struct 
> device *dev, uuid_le uuid)
>   if (!parent)
>   return -EINVAL;
>  
> - mutex_lock(>lock);
> + mutex_lock(_list_lock);
>  
>   /* Check for duplicate */
> - if (mdev_device_exist(parent, uuid)) {
> - ret = -EEXIST;
> - goto create_err;
> + list_for_each_entry(tmp, _list, next) {
> + if (!uuid_le_cmp(tmp->uuid, uuid)) {
> + ret = -EEXIST;
> + goto create_err;
> + }
>   }
>
Is it possible to use mdev_list_lock for as minimal portion as possible?
By adding mdev device to mdev_list just after:
memcpy(>uuid, , sizeof(uuid_le));
and then unlock mdev_list_lock, but at the same time all later error
cases need to be handled properly in this function.

Thanks,
Kirti


>   mdev = kzalloc(sizeof(*mdev), GFP_KERNEL);
> @@ -354,9 +327,6 @@ int mdev_device_create(struct kobject *kobj, struct 
> device *dev, uuid_le uuid)
>   mdev->type_kobj = kobj;
>   dev_dbg(>dev, "MDEV: created\n");
>  
> - mutex_unlock(>lock);
> -
> - mutex_lock(_list_lock);
>   

Re: [PATCH v2] vfio/mdev: Check globally for duplicate devices

[Kirti Wankhede]

On 5/16/2018 8:53 PM, Alex Williamson wrote:
> When we create an mdev device, we check for duplicates against the
> parent device and return -EEXIST if found, but the mdev device
> namespace is global since we'll link all devices from the bus.  We do
> catch this later in sysfs_do_create_link_sd() to return -EEXIST, but
> with it comes a kernel warning and stack trace for trying to create
> duplicate sysfs links, which makes it an undesirable response.
> 
> Therefore we should really be looking for duplicates across all mdev
> parent devices, or as implemented here, against our mdev device list.
> 
> Notably, mdev_parent.lock really only seems to be serializing device
> creation and removal per parent.  I'm not sure if this is necessary,
> mdev vendor drivers could easily provide this serialization if it
> is required, but a side-effect of holding the mdev_list_lock to
> protect the namespace is actually greater serialization across the
> create and remove paths,

Exactly for this reason more granular lock is used and that's the reason
mdev_parent.lock was introduced. Consider the max supported config for
vGPU: 8 GPUs in a system with 16 mdev devices on each GPUs, i.e. 128
mdev devices need to be created in a system, and this count will
increase in future, all mdev device creation/removal will get serialized
with this change.
I agree with your concern that if there are duplicates across parents,
its not caught earlier.

> so mdev_parent.lock is removed.  If we can
> show that vendor drivers handle the create/remove paths themselves,
> perhaps we can refine the locking granularity.
> 

Here lock is not for create/remove routines of vendor driver, its about
mdev device creation and device registration, which is a common code
path, and so is part of mdev core module.


> Reviewed-by: Cornelia Huck 
> Signed-off-by: Alex Williamson 
> ---
> 
> v2: Remove unnecessary ret init per Cornelia's review
> 
>  drivers/vfio/mdev/mdev_core.c|   77 
> +-
>  drivers/vfio/mdev/mdev_private.h |1 
>  2 files changed, 19 insertions(+), 59 deletions(-)
> 
> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> index 126991046eb7..aaab3ef93e1c 100644
> --- a/drivers/vfio/mdev/mdev_core.c
> +++ b/drivers/vfio/mdev/mdev_core.c
> @@ -66,34 +66,6 @@ uuid_le mdev_uuid(struct mdev_device *mdev)
>  }
>  EXPORT_SYMBOL(mdev_uuid);
>  
> -static int _find_mdev_device(struct device *dev, void *data)
> -{
> - struct mdev_device *mdev;
> -
> - if (!dev_is_mdev(dev))
> - return 0;
> -
> - mdev = to_mdev_device(dev);
> -
> - if (uuid_le_cmp(mdev->uuid, *(uuid_le *)data) == 0)
> - return 1;
> -
> - return 0;
> -}
> -
> -static bool mdev_device_exist(struct mdev_parent *parent, uuid_le uuid)
> -{
> - struct device *dev;
> -
> - dev = device_find_child(parent->dev, , _find_mdev_device);
> - if (dev) {
> - put_device(dev);
> - return true;
> - }
> -
> - return false;
> -}
> -
>  /* Should be called holding parent_list_lock */
>  static struct mdev_parent *__find_parent_device(struct device *dev)
>  {
> @@ -221,7 +193,6 @@ int mdev_register_device(struct device *dev, const struct 
> mdev_parent_ops *ops)
>   }
>  
>   kref_init(>ref);
> - mutex_init(>lock);
>  
>   parent->dev = dev;
>   parent->ops = ops;
> @@ -304,7 +275,7 @@ static void mdev_device_release(struct device *dev)
>  int mdev_device_create(struct kobject *kobj, struct device *dev, uuid_le 
> uuid)
>  {
>   int ret;
> - struct mdev_device *mdev;
> + struct mdev_device *mdev, *tmp;
>   struct mdev_parent *parent;
>   struct mdev_type *type = to_mdev_type(kobj);
>  
> @@ -312,12 +283,14 @@ int mdev_device_create(struct kobject *kobj, struct 
> device *dev, uuid_le uuid)
>   if (!parent)
>   return -EINVAL;
>  
> - mutex_lock(>lock);
> + mutex_lock(_list_lock);
>  
>   /* Check for duplicate */
> - if (mdev_device_exist(parent, uuid)) {
> - ret = -EEXIST;
> - goto create_err;
> + list_for_each_entry(tmp, _list, next) {
> + if (!uuid_le_cmp(tmp->uuid, uuid)) {
> + ret = -EEXIST;
> + goto create_err;
> + }
>   }
>
Is it possible to use mdev_list_lock for as minimal portion as possible?
By adding mdev device to mdev_list just after:
memcpy(>uuid, , sizeof(uuid_le));
and then unlock mdev_list_lock, but at the same time all later error
cases need to be handled properly in this function.

Thanks,
Kirti


>   mdev = kzalloc(sizeof(*mdev), GFP_KERNEL);
> @@ -354,9 +327,6 @@ int mdev_device_create(struct kobject *kobj, struct 
> device *dev, uuid_le uuid)
>   mdev->type_kobj = kobj;
>   dev_dbg(>dev, "MDEV: created\n");
>  
> - mutex_unlock(>lock);
> -
> - mutex_lock(_list_lock);
>   list_add(>next, _list);
>   mutex_unlock(_list_lock);
>