| Message ID | 20170707220933.30799.16747.stgit@gimli.home (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 08/07/17 08:15, Alex Williamson wrote: > 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: Chuanxiao Dong <chuanxiao.dong@intel.com> > Signed-off-by: Alex Williamson <alex.williamson@redhat.com> > --- > > Alexey, does the SPAPR/TCE iommu backend have any dependencies on this > lock? If so, let's create a lock in the spapr_tce backend like we > have in type1 to handle it. There is one already - tce_container::lock. > I believe the ioctl passthrough is the > only interface that can reach spapr_tce. There are also vfio_iommu_driver_ops::attach_group/detach_group but these are also using tce_container::lock so spapr is going to be fine. Acked-by: Alexey Kardashevskiy <aik@ozlabs.ru> > Thanks, > > Alex > > drivers/vfio/vfio.c | 38 -------------------------------------- > 1 file changed, 38 deletions(-) > > diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c > index 7597a377eb4e..330d50582f40 100644 > --- a/drivers/vfio/vfio.c > +++ b/drivers/vfio/vfio.c > @@ -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; >
Sounds reasonable to me. Thanks, Kirti On 7/8/2017 3:45 AM, Alex Williamson wrote: > 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: Chuanxiao Dong <chuanxiao.dong@intel.com> > Signed-off-by: Alex Williamson <alex.williamson@redhat.com> > --- > > Alexey, does the SPAPR/TCE iommu backend have any dependencies on this > lock? If so, let's create a lock in the spapr_tce backend like we > have in type1 to handle it. I believe the ioctl passthrough is the > only interface that can reach spapr_tce. Thanks, > > Alex > > drivers/vfio/vfio.c | 38 -------------------------------------- > 1 file changed, 38 deletions(-) > > diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c > index 7597a377eb4e..330d50582f40 100644 > --- a/drivers/vfio/vfio.c > +++ b/drivers/vfio/vfio.c > @@ -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; >
diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c index 7597a377eb4e..330d50582f40 100644 --- a/drivers/vfio/vfio.c +++ b/drivers/vfio/vfio.c @@ -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;
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: Chuanxiao Dong <chuanxiao.dong@intel.com> Signed-off-by: Alex Williamson <alex.williamson@redhat.com> --- Alexey, does the SPAPR/TCE iommu backend have any dependencies on this lock? If so, let's create a lock in the spapr_tce backend like we have in type1 to handle it. I believe the ioctl passthrough is the only interface that can reach spapr_tce. Thanks, Alex drivers/vfio/vfio.c | 38 -------------------------------------- 1 file changed, 38 deletions(-)