Commit 7f56c30b authored by Alex Williamson's avatar Alex Williamson
Browse files

vfio: Remove unnecessary uses of vfio_container.group_lock 



The original intent of vfio_container.group_lock is to protect
vfio_container.group_list, however over time it's become a crutch to
prevent changes in container composition any time we call into the
iommu driver backend.  This introduces problems when we start to have
more complex interactions, for example when a user's DMA unmap request
triggers a notification to an mdev vendor driver, who responds by
attempting to unpin mappings within that request, re-entering the
iommu backend.  We incorrectly assume that the use of read-locks here
allow for this nested locking behavior, but a poorly timed write-lock
could in fact trigger a deadlock.

The current use of group_lock seems to fall into the trap of locking
code, not data.  Correct that by removing uses of group_lock that are
not directly related to group_list.  Note that the vfio type1 iommu
backend has its own mutex, vfio_iommu.lock, which it uses to protect
itself for each of these interfaces anyway.  The group_lock appears to
be a redundancy for these interfaces and type1 even goes so far as to
release its mutex to allow for exactly the re-entrant code path above.

Reported-by: default avatarChuanxiao Dong <chuanxiao.dong@intel.com>
Signed-off-by: default avatarAlex Williamson <alex.williamson@redhat.com>
Acked-by: default avatarAlexey Kardashevskiy <aik@ozlabs.ru>
Cc: stable@vger.kernel.org # v4.10+
parent 5d6dee80

drivers/vfio/vfio.c

+0 −38
Original line number Diff line number Diff line
@@ -1175,15 +1175,11 @@ static long vfio_fops_unl_ioctl(struct file *filep, 
		ret = vfio_ioctl_set_iommu(container, arg);

		break;

	default:

		down_read(&container->group_lock);



		driver = container->iommu_driver;

		data = container->iommu_data;



		if (driver) /* passthrough all unrecognized ioctls */

			ret = driver->ops->ioctl(data, cmd, arg);



		up_read(&container->group_lock);

	}



	return ret;
@@ -1237,15 +1233,11 @@ static ssize_t vfio_fops_read(struct file *filep, char __user *buf, 
	struct vfio_iommu_driver *driver;

	ssize_t ret = -EINVAL;



	down_read(&container->group_lock);



	driver = container->iommu_driver;

	if (likely(driver && driver->ops->read))

		ret = driver->ops->read(container->iommu_data,

					buf, count, ppos);



	up_read(&container->group_lock);



	return ret;

}
@@ -1256,15 +1248,11 @@ static ssize_t vfio_fops_write(struct file *filep, const char __user *buf, 
	struct vfio_iommu_driver *driver;

	ssize_t ret = -EINVAL;



	down_read(&container->group_lock);



	driver = container->iommu_driver;

	if (likely(driver && driver->ops->write))

		ret = driver->ops->write(container->iommu_data,

					 buf, count, ppos);



	up_read(&container->group_lock);



	return ret;

}
@@ -1274,14 +1262,10 @@ static int vfio_fops_mmap(struct file *filep, struct vm_area_struct *vma) 
	struct vfio_iommu_driver *driver;

	int ret = -EINVAL;



	down_read(&container->group_lock);



	driver = container->iommu_driver;

	if (likely(driver && driver->ops->mmap))

		ret = driver->ops->mmap(container->iommu_data, vma);



	up_read(&container->group_lock);



	return ret;

}
@@ -1993,8 +1977,6 @@ int vfio_pin_pages(struct device *dev, unsigned long *user_pfn, int npage, 
		goto err_pin_pages;



	container = group->container;

	down_read(&container->group_lock);



	driver = container->iommu_driver;

	if (likely(driver && driver->ops->pin_pages))

		ret = driver->ops->pin_pages(container->iommu_data, user_pfn,
@@ -2002,7 +1984,6 @@ int vfio_pin_pages(struct device *dev, unsigned long *user_pfn, int npage, 
	else

		ret = -ENOTTY;



	up_read(&container->group_lock);

	vfio_group_try_dissolve_container(group);



err_pin_pages:
@@ -2042,8 +2023,6 @@ int vfio_unpin_pages(struct device *dev, unsigned long *user_pfn, int npage) 
		goto err_unpin_pages;



	container = group->container;

	down_read(&container->group_lock);



	driver = container->iommu_driver;

	if (likely(driver && driver->ops->unpin_pages))

		ret = driver->ops->unpin_pages(container->iommu_data, user_pfn,
@@ -2051,7 +2030,6 @@ int vfio_unpin_pages(struct device *dev, unsigned long *user_pfn, int npage) 
	else

		ret = -ENOTTY;



	up_read(&container->group_lock);

	vfio_group_try_dissolve_container(group);



err_unpin_pages:
@@ -2073,8 +2051,6 @@ static int vfio_register_iommu_notifier(struct vfio_group *group, 
		return -EINVAL;



	container = group->container;

	down_read(&container->group_lock);



	driver = container->iommu_driver;

	if (likely(driver && driver->ops->register_notifier))

		ret = driver->ops->register_notifier(container->iommu_data,
@@ -2082,7 +2058,6 @@ static int vfio_register_iommu_notifier(struct vfio_group *group, 
	else

		ret = -ENOTTY;



	up_read(&container->group_lock);

	vfio_group_try_dissolve_container(group);



	return ret;
@@ -2100,8 +2075,6 @@ static int vfio_unregister_iommu_notifier(struct vfio_group *group, 
		return -EINVAL;



	container = group->container;

	down_read(&container->group_lock);



	driver = container->iommu_driver;

	if (likely(driver && driver->ops->unregister_notifier))

		ret = driver->ops->unregister_notifier(container->iommu_data,
@@ -2109,7 +2082,6 @@ static int vfio_unregister_iommu_notifier(struct vfio_group *group, 
	else

		ret = -ENOTTY;



	up_read(&container->group_lock);

	vfio_group_try_dissolve_container(group);



	return ret;
@@ -2127,7 +2099,6 @@ static int vfio_register_group_notifier(struct vfio_group *group, 
					unsigned long *events,

					struct notifier_block *nb)

{

	struct vfio_container *container;

	int ret;

	bool set_kvm = false;
@@ -2145,9 +2116,6 @@ static int vfio_register_group_notifier(struct vfio_group *group, 
	if (ret)

		return -EINVAL;



	container = group->container;

	down_read(&container->group_lock);



	ret = blocking_notifier_chain_register(&group->notifier, nb);



	/*
@@ -2158,7 +2126,6 @@ static int vfio_register_group_notifier(struct vfio_group *group, 
		blocking_notifier_call_chain(&group->notifier,

					VFIO_GROUP_NOTIFY_SET_KVM, group->kvm);



	up_read(&container->group_lock);

	vfio_group_try_dissolve_container(group);



	return ret;
@@ -2167,19 +2134,14 @@ static int vfio_register_group_notifier(struct vfio_group *group, 
static int vfio_unregister_group_notifier(struct vfio_group *group,

					 struct notifier_block *nb)

{

	struct vfio_container *container;

	int ret;



	ret = vfio_group_add_container_user(group);

	if (ret)

		return -EINVAL;



	container = group->container;

	down_read(&container->group_lock);



	ret = blocking_notifier_chain_unregister(&group->notifier, nb);



	up_read(&container->group_lock);

	vfio_group_try_dissolve_container(group);



	return ret;

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