[PATCH 37/37] vfio: Add support for Shared Virtual Addressing

[Jean-Philippe Brucker <jean-philippe.brucker@arm.com>]

Add two new ioctl for VFIO containers. VFIO_IOMMU_BIND_PROCESS creates a
bond between a container and a process address space, identified by a
device-specific ID named PASID. This allows the device to target DMA
transactions at the process virtual addresses without a need for mapping
and unmapping buffers explicitly in the IOMMU. The process page tables are
shared with the IOMMU, and mechanisms such as PCI ATS/PRI are used to
handle faults. VFIO_IOMMU_UNBIND_PROCESS removes a bond created with
VFIO_IOMMU_BIND_PROCESS.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
---
 drivers/vfio/vfio_iommu_type1.c | 399 ++++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/vfio.h       |  76 ++++++++
 2 files changed, 475 insertions(+)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index e30e29ae4819..cac066f0026b 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -30,6 +30,7 @@
 #include <linux/iommu.h>
 #include <linux/module.h>
 #include <linux/mm.h>
+#include <linux/ptrace.h>
 #include <linux/rbtree.h>
 #include <linux/sched/signal.h>
 #include <linux/sched/mm.h>
@@ -60,6 +61,7 @@ MODULE_PARM_DESC(disable_hugepages,
 
 struct vfio_iommu {
 	struct list_head	domain_list;
+	struct list_head	mm_list;
 	struct vfio_domain	*external_domain; /* domain for external user */
 	struct mutex		lock;
 	struct rb_root		dma_list;
@@ -90,6 +92,15 @@ struct vfio_dma {
 struct vfio_group {
 	struct iommu_group	*iommu_group;
 	struct list_head	next;
+	bool			sva_enabled;
+};
+
+struct vfio_mm {
+#define VFIO_PASID_INVALID	(-1)
+	spinlock_t		lock;
+	int			pasid;
+	struct mm_struct	*mm;
+	struct list_head	next;
 };
 
 /*
@@ -1117,6 +1128,157 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
 	return 0;
 }
 
+static int vfio_iommu_mm_exit(struct device *dev, int pasid, void *data)
+{
+	struct vfio_mm *vfio_mm = data;
+
+	/*
+	 * The mm_exit callback cannot block, so we can't take the iommu mutex
+	 * and remove this vfio_mm from the list. Hopefully the SVA code will
+	 * relax its locking requirement in the future.
+	 *
+	 * We mostly care about attach_group, which will attempt to replay all
+	 * binds in this container. Ensure that it doesn't touch this defunct mm
+	 * struct, by clearing the pointer. The structure will be freed when the
+	 * group is removed from the container.
+	 */
+	spin_lock(&vfio_mm->lock);
+	vfio_mm->mm = NULL;
+	spin_unlock(&vfio_mm->lock);
+
+	return 0;
+}
+
+static int vfio_iommu_sva_init(struct device *dev, void *data)
+{
+
+	int ret;
+
+	ret = iommu_sva_device_init(dev, IOMMU_SVA_FEAT_PASID |
+				    IOMMU_SVA_FEAT_IOPF, 0);
+	if (ret)
+		return ret;
+
+	return iommu_register_mm_exit_handler(dev, vfio_iommu_mm_exit);
+}
+
+static int vfio_iommu_sva_shutdown(struct device *dev, void *data)
+{
+	iommu_sva_device_shutdown(dev);
+	iommu_unregister_mm_exit_handler(dev);
+
+	return 0;
+}
+
+static int vfio_iommu_bind_group(struct vfio_iommu *iommu,
+				 struct vfio_group *group,
+				 struct vfio_mm *vfio_mm)
+{
+	int ret;
+	int pasid;
+
+	if (!group->sva_enabled) {
+		ret = iommu_group_for_each_dev(group->iommu_group, NULL,
+					       vfio_iommu_sva_init);
+		if (ret)
+			return ret;
+
+		group->sva_enabled = true;
+	}
+
+	ret = iommu_sva_bind_group(group->iommu_group, vfio_mm->mm, &pasid,
+				   IOMMU_SVA_FEAT_PASID | IOMMU_SVA_FEAT_IOPF,
+				   vfio_mm);
+	if (ret)
+		return ret;
+
+	if (WARN_ON(vfio_mm->pasid != VFIO_PASID_INVALID && pasid !=
+		    vfio_mm->pasid))
+		return -EFAULT;
+
+	vfio_mm->pasid = pasid;
+
+	return 0;
+}
+
+static void vfio_iommu_unbind_group(struct vfio_group *group,
+				    struct vfio_mm *vfio_mm)
+{
+	iommu_sva_unbind_group(group->iommu_group, vfio_mm->pasid);
+}
+
+static void vfio_iommu_unbind(struct vfio_iommu *iommu,
+			      struct vfio_mm *vfio_mm)
+{
+	struct vfio_group *group;
+	struct vfio_domain *domain;
+
+	list_for_each_entry(domain, &iommu->domain_list, next)
+		list_for_each_entry(group, &domain->group_list, next)
+			vfio_iommu_unbind_group(group, vfio_mm);
+}
+
+static bool vfio_mm_get(struct vfio_mm *vfio_mm)
+{
+	bool ret;
+
+	spin_lock(&vfio_mm->lock);
+	ret = vfio_mm->mm && mmget_not_zero(vfio_mm->mm);
+	spin_unlock(&vfio_mm->lock);
+
+	return ret;
+}
+
+static void vfio_mm_put(struct vfio_mm *vfio_mm)
+{
+	mmput(vfio_mm->mm);
+}
+
+static int vfio_iommu_replay_bind(struct vfio_iommu *iommu, struct vfio_group *group)
+{
+	int ret = 0;
+	struct vfio_mm *vfio_mm;
+
+	list_for_each_entry(vfio_mm, &iommu->mm_list, next) {
+		/*
+		 * Ensure mm doesn't exit while we're binding it to the new
+		 * group.
+		 */
+		if (!vfio_mm_get(vfio_mm))
+			continue;
+		ret = vfio_iommu_bind_group(iommu, group, vfio_mm);
+		vfio_mm_put(vfio_mm);
+
+		if (ret)
+			goto out_unbind;
+	}
+
+	return 0;
+
+out_unbind:
+	list_for_each_entry_continue_reverse(vfio_mm, &iommu->mm_list, next) {
+		if (!vfio_mm_get(vfio_mm))
+			continue;
+		iommu_sva_unbind_group(group->iommu_group, vfio_mm->pasid);
+		vfio_mm_put(vfio_mm);
+	}
+
+	return ret;
+}
+
+static void vfio_iommu_free_all_mm(struct vfio_iommu *iommu)
+{
+	struct vfio_mm *vfio_mm, *tmp;
+
+	/*
+	 * No need for unbind() here. Since all groups are detached from this
+	 * iommu, bonds have been removed.
+	 */
+	list_for_each_entry_safe(vfio_mm, tmp, &iommu->mm_list, next)
+		kfree(vfio_mm);
+	INIT_LIST_HEAD(&iommu->mm_list);
+}
+
 /*
  * We change our unmap behavior slightly depending on whether the IOMMU
  * supports fine-grained superpages.  IOMMUs like AMD-Vi will use a superpage
@@ -1301,6 +1463,15 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
 		    d->prot == domain->prot) {
 			iommu_detach_group(domain->domain, iommu_group);
 			if (!iommu_attach_group(d->domain, iommu_group)) {
+				if (vfio_iommu_replay_bind(iommu, group)) {
+					iommu_detach_group(d->domain, iommu_group);
+					ret = iommu_attach_group(domain->domain,
+								 iommu_group);
+					if (ret)
+						goto out_domain;
+					continue;
+				}
+
 				list_add(&group->next, &d->group_list);
 				iommu_domain_free(domain->domain);
 				kfree(domain);
@@ -1321,6 +1492,10 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
 	if (ret)
 		goto out_detach;
 
+	ret = vfio_iommu_replay_bind(iommu, group);
+	if (ret)
+		goto out_detach;
+
 	if (resv_msi) {
 		ret = iommu_get_msi_cookie(domain->domain, resv_msi_base);
 		if (ret)
@@ -1426,6 +1601,11 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
 			continue;
 
 		iommu_detach_group(domain->domain, iommu_group);
+		if (group->sva_enabled) {
+			iommu_group_for_each_dev(iommu_group, NULL,
+						 vfio_iommu_sva_shutdown);
+			group->sva_enabled = false;
+		}
 		list_del(&group->next);
 		kfree(group);
 		/*
@@ -1441,6 +1621,7 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
 					vfio_iommu_unmap_unpin_all(iommu);
 				else
 					vfio_iommu_unmap_unpin_reaccount(iommu);
+				vfio_iommu_free_all_mm(iommu);
 			}
 			iommu_domain_free(domain->domain);
 			list_del(&domain->next);
@@ -1475,6 +1656,7 @@ static void *vfio_iommu_type1_open(unsigned long arg)
 	}
 
 	INIT_LIST_HEAD(&iommu->domain_list);
+	INIT_LIST_HEAD(&iommu->mm_list);
 	iommu->dma_list = RB_ROOT;
 	mutex_init(&iommu->lock);
 	BLOCKING_INIT_NOTIFIER_HEAD(&iommu->notifier);
@@ -1509,6 +1691,7 @@ static void vfio_iommu_type1_release(void *iommu_data)
 		kfree(iommu->external_domain);
 	}
 
+	vfio_iommu_free_all_mm(iommu);
 	vfio_iommu_unmap_unpin_all(iommu);
 
 	list_for_each_entry_safe(domain, domain_tmp,
@@ -1537,6 +1720,184 @@ static int vfio_domains_have_iommu_cache(struct vfio_iommu *iommu)
 	return ret;
 }
 
+static struct mm_struct *vfio_iommu_get_mm_by_vpid(pid_t vpid)
+{
+	struct mm_struct *mm;
+	struct task_struct *task;
+
+	rcu_read_lock();
+	task = find_task_by_vpid(vpid);
+	if (task)
+		get_task_struct(task);
+	rcu_read_unlock();
+	if (!task)
+		return ERR_PTR(-ESRCH);
+
+	/* Ensure that current has RW access on the mm */
+	mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
+	put_task_struct(task);
+
+	if (!mm)
+		return ERR_PTR(-ESRCH);
+
+	return mm;
+}
+
+static long vfio_iommu_type1_bind_process(struct vfio_iommu *iommu,
+					  void __user *arg,
+					  struct vfio_iommu_type1_bind *bind)
+{
+	struct vfio_iommu_type1_bind_process params;
+	struct vfio_domain *domain;
+	struct vfio_group *group;
+	struct vfio_mm *vfio_mm;
+	struct mm_struct *mm;
+	unsigned long minsz;
+	int ret = 0;
+
+	minsz = sizeof(*bind) + sizeof(params);
+	if (bind->argsz < minsz)
+		return -EINVAL;
+
+	arg += sizeof(*bind);
+	if (copy_from_user(&params, arg, sizeof(params)))
+		return -EFAULT;
+
+	if (params.flags & ~VFIO_IOMMU_BIND_PID)
+		return -EINVAL;
+
+	if (params.flags & VFIO_IOMMU_BIND_PID) {
+		mm = vfio_iommu_get_mm_by_vpid(params.pid);
+		if (IS_ERR(mm))
+			return PTR_ERR(mm);
+	} else {
+		mm = get_task_mm(current);
+		if (!mm)
+			return -EINVAL;
+	}
+
+	mutex_lock(&iommu->lock);
+	if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu)) {
+		ret = -EINVAL;
+		goto out_put_mm;
+	}
+
+	list_for_each_entry(vfio_mm, &iommu->mm_list, next) {
+		if (vfio_mm->mm != mm)
+			continue;
+
+		params.pasid = vfio_mm->pasid;
+
+		ret = copy_to_user(arg, &params, sizeof(params)) ? -EFAULT : 0;
+		goto out_put_mm;
+	}
+
+	vfio_mm = kzalloc(sizeof(*vfio_mm), GFP_KERNEL);
+	if (!vfio_mm) {
+		ret = -ENOMEM;
+		goto out_put_mm;
+	}
+
+	vfio_mm->mm = mm;
+	vfio_mm->pasid = VFIO_PASID_INVALID;
+	spin_lock_init(&vfio_mm->lock);
+
+	list_for_each_entry(domain, &iommu->domain_list, next) {
+		list_for_each_entry(group, &domain->group_list, next) {
+			ret = vfio_iommu_bind_group(iommu, group, vfio_mm);
+			if (ret)
+				break;
+		}
+		if (ret)
+			break;
+	}
+
+	if (ret) {
+		/* Undo all binds that already succeeded */
+		list_for_each_entry_continue_reverse(group, &domain->group_list,
+						     next)
+			vfio_iommu_unbind_group(group, vfio_mm);
+		list_for_each_entry_continue_reverse(domain, &iommu->domain_list,
+						     next)
+			list_for_each_entry(group, &domain->group_list, next)
+				vfio_iommu_unbind_group(group, vfio_mm);
+		kfree(vfio_mm);
+	} else {
+		list_add(&vfio_mm->next, &iommu->mm_list);
+
+		params.pasid = vfio_mm->pasid;
+		ret = copy_to_user(arg, &params, sizeof(params)) ? -EFAULT : 0;
+		if (ret) {
+			vfio_iommu_unbind(iommu, vfio_mm);
+			kfree(vfio_mm);
+		}
+	}
+
+out_put_mm:
+	mutex_unlock(&iommu->lock);
+	mmput(mm);
+
+	return ret;
+}
+
+static long vfio_iommu_type1_unbind_process(struct vfio_iommu *iommu,
+					    void __user *arg,
+					    struct vfio_iommu_type1_bind *bind)
+{
+	int ret = -EINVAL;
+	unsigned long minsz;
+	struct mm_struct *mm;
+	struct vfio_mm *vfio_mm;
+	struct vfio_iommu_type1_bind_process params;
+
+	minsz = sizeof(*bind) + sizeof(params);
+	if (bind->argsz < minsz)
+		return -EINVAL;
+
+	arg += sizeof(*bind);
+	if (copy_from_user(&params, arg, sizeof(params)))
+		return -EFAULT;
+
+	if (params.flags & ~VFIO_IOMMU_BIND_PID)
+		return -EINVAL;
+
+	/*
+	 * We can't simply unbind a foreign process by PASID, because the
+	 * process might have died and the PASID might have been reallocated to
+	 * another process. Instead we need to fetch that process mm by PID
+	 * again to make sure we remove the right vfio_mm. In addition, holding
+	 * the mm guarantees that mm_users isn't dropped while we unbind and the
+	 * exit_mm handler doesn't fire. While not strictly necessary, not
+	 * having to care about that race simplifies everyone's life.
+	 */
+	if (params.flags & VFIO_IOMMU_BIND_PID) {
+		mm = vfio_iommu_get_mm_by_vpid(params.pid);
+		if (IS_ERR(mm))
+			return PTR_ERR(mm);
+	} else {
+		mm = get_task_mm(current);
+		if (!mm)
+			return -EINVAL;
+	}
+
+	ret = -ESRCH;
+	mutex_lock(&iommu->lock);
+	list_for_each_entry(vfio_mm, &iommu->mm_list, next) {
+		if (vfio_mm->mm != mm)
+			continue;
+
+		vfio_iommu_unbind(iommu, vfio_mm);
+		list_del(&vfio_mm->next);
+		kfree(vfio_mm);
+		ret = 0;
+		break;
+	}
+	mutex_unlock(&iommu->lock);
+	mmput(mm);
+
+	return ret;
+}
+
 static long vfio_iommu_type1_ioctl(void *iommu_data,
 				   unsigned int cmd, unsigned long arg)
 {
@@ -1607,6 +1968,44 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
 
 		return copy_to_user((void __user *)arg, &unmap, minsz) ?
 			-EFAULT : 0;
+
+	} else if (cmd == VFIO_IOMMU_BIND) {
+		struct vfio_iommu_type1_bind bind;
+
+		minsz = offsetofend(struct vfio_iommu_type1_bind, mode);
+
+		if (copy_from_user(&bind, (void __user *)arg, minsz))
+			return -EFAULT;
+
+		if (bind.argsz < minsz)
+			return -EINVAL;
+
+		switch (bind.mode) {
+		case VFIO_IOMMU_BIND_PROCESS:
+			return vfio_iommu_type1_bind_process(iommu, (void *)arg,
+							     &bind);
+		default:
+			return -EINVAL;
+		}
+
+	} else if (cmd == VFIO_IOMMU_UNBIND) {
+		struct vfio_iommu_type1_bind bind;
+
+		minsz = offsetofend(struct vfio_iommu_type1_bind, mode);
+
+		if (copy_from_user(&bind, (void __user *)arg, minsz))
+			return -EFAULT;
+
+		if (bind.argsz < minsz)
+			return -EINVAL;
+
+		switch (bind.mode) {
+		case VFIO_IOMMU_BIND_PROCESS:
+			return vfio_iommu_type1_unbind_process(iommu, (void *)arg,
+							       &bind);
+		default:
+			return -EINVAL;
+		}
 	}
 
 	return -ENOTTY;
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index c74372163ed2..e1b9b8c58916 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -638,6 +638,82 @@ struct vfio_iommu_type1_dma_unmap {
 #define VFIO_IOMMU_ENABLE	_IO(VFIO_TYPE, VFIO_BASE + 15)
 #define VFIO_IOMMU_DISABLE	_IO(VFIO_TYPE, VFIO_BASE + 16)
 
+/*
+ * VFIO_IOMMU_BIND_PROCESS
+ *
+ * Allocate a PASID for a process address space, and use it to attach this
+ * process to all devices in the container. Devices can then tag their DMA
+ * traffic with the returned @pasid to perform transactions on the associated
+ * virtual address space. Mapping and unmapping buffers is performed by standard
+ * functions such as mmap and malloc.
+ *
+ * If flag is VFIO_IOMMU_BIND_PID, @pid contains the pid of a foreign process to
+ * bind. Otherwise the current task is bound. Given that the caller owns the
+ * device, setting this flag grants the caller read and write permissions on the
+ * entire address space of foreign process described by @pid. Therefore,
+ * permission to perform the bind operation on a foreign process is governed by
+ * the ptrace access mode PTRACE_MODE_ATTACH_REALCREDS check. See man ptrace(2)
+ * for more information.
+ *
+ * On success, VFIO writes a Process Address Space ID (PASID) into @pasid. This
+ * ID is unique to a process and can be used on all devices in the container.
+ *
+ * On fork, the child inherits the device fd and can use the bonds setup by its
+ * parent. Consequently, the child has R/W access on the address spaces bound by
+ * its parent. After an execv, the device fd is closed and the child doesn't
+ * have access to the address space anymore.
+ *
+ * To remove a bond between process and container, VFIO_IOMMU_UNBIND ioctl is
+ * issued with the same parameters. If a pid was specified in VFIO_IOMMU_BIND,
+ * it should also be present for VFIO_IOMMU_UNBIND. Otherwise unbind the current
+ * task from the container.
+ */
+struct vfio_iommu_type1_bind_process {
+	__u32	flags;
+#define VFIO_IOMMU_BIND_PID		(1 << 0)
+	__u32	pasid;
+	__s32	pid;
+};
+
+/*
+ * Only mode supported at the moment is VFIO_IOMMU_BIND_PROCESS, which takes
+ * vfio_iommu_type1_bind_process in data.
+ */
+struct vfio_iommu_type1_bind {
+	__u32	argsz;
+	__u32	mode;
+#define VFIO_IOMMU_BIND_PROCESS		(1 << 0)
+	__u8	data[];
+};
+
+/*
+ * VFIO_IOMMU_BIND - _IOWR(VFIO_TYPE, VFIO_BASE + 22, struct vfio_iommu_bind)
+ *
+ * Manage address spaces of devices in this container. Initially a TYPE1
+ * container can only have one address space, managed with
+ * VFIO_IOMMU_MAP/UNMAP_DMA.
+ *
+ * An IOMMU of type VFIO_TYPE1_NESTING_IOMMU can be managed by both MAP/UNMAP
+ * and BIND ioctls at the same time. MAP/UNMAP acts on the stage-2 (host) page
+ * tables, and BIND manages the stage-1 (guest) page tables. Other types of
+ * IOMMU may allow MAP/UNMAP and BIND to coexist, where MAP/UNMAP controls
+ * non-PASID traffic and BIND controls PASID traffic. But this depends on the
+ * underlying IOMMU architecture and isn't guaranteed.
+ *
+ * Availability of this feature depends on the device, its bus, the underlying
+ * IOMMU and the CPU architecture.
+ *
+ * returns: 0 on success, -errno on failure.
+ */
+#define VFIO_IOMMU_BIND		_IO(VFIO_TYPE, VFIO_BASE + 22)
+
+/*
+ * VFIO_IOMMU_UNBIND - _IOWR(VFIO_TYPE, VFIO_BASE + 23, struct vfio_iommu_bind)
+ *
+ * Undo what was done by the corresponding VFIO_IOMMU_BIND ioctl.
+ */
+#define VFIO_IOMMU_UNBIND	_IO(VFIO_TYPE, VFIO_BASE + 23)
+
 /* -------- Additional API for SPAPR TCE (Server POWERPC) IOMMU -------- */
 
 /*
-- 
2.15.1