iommufd: Implement sw_msi support natively

iommufd has a model where the iommu_domain can be changed while the VFIO
device is attached. In this case, the MSI should continue to work. This
corner case has not worked because the dma-iommu implementation of sw_msi
is tied to a single domain.

Implement the sw_msi mapping directly and use a global per-fd table to
associate assigned IOVA to the MSI pages. This allows the MSI pages to
be loaded into a domain before it is attached ensuring that MSI is not
disrupted.

Link: https://patch.msgid.link/r/e13d23eeacd67c0a692fc468c85b483f4dd51c57.1740014950.git.nicolinc@nvidia.com
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/iommu/iommufd/device.c

@@ -5,6 +5,7 @@
 #include <linux/iommufd.h>
 #include <linux/slab.h>
 #include <uapi/linux/iommufd.h>
+#include <linux/msi.h>
 
 #include "../iommu-priv.h"
 #include "io_pagetable.h"
@@ -293,36 +294,152 @@ u32 iommufd_device_to_id(struct iommufd_device *idev)
 }
 EXPORT_SYMBOL_NS_GPL(iommufd_device_to_id, "IOMMUFD");
 
-static int iommufd_group_setup_msi(struct iommufd_group *igroup,
-				   struct iommufd_hwpt_paging *hwpt_paging)
+/*
+ * Get a iommufd_sw_msi_map for the msi physical address requested by the irq
+ * layer. The mapping to IOVA is global to the iommufd file descriptor, every
+ * domain that is attached to a device using the same MSI parameters will use
+ * the same IOVA.
+ */
+static __maybe_unused struct iommufd_sw_msi_map *
+iommufd_sw_msi_get_map(struct iommufd_ctx *ictx, phys_addr_t msi_addr,
+		       phys_addr_t sw_msi_start)
 {
-	phys_addr_t sw_msi_start = igroup->sw_msi_start;
+	struct iommufd_sw_msi_map *cur;
+	unsigned int max_pgoff = 0;
+
+	lockdep_assert_held(&ictx->sw_msi_lock);
+
+	list_for_each_entry(cur, &ictx->sw_msi_list, sw_msi_item) {
+		if (cur->sw_msi_start != sw_msi_start)
+			continue;
+		max_pgoff = max(max_pgoff, cur->pgoff + 1);
+		if (cur->msi_addr == msi_addr)
+			return cur;
+	}
+
+	if (ictx->sw_msi_id >=
+	    BITS_PER_BYTE * sizeof_field(struct iommufd_sw_msi_maps, bitmap))
+		return ERR_PTR(-EOVERFLOW);
+
+	cur = kzalloc(sizeof(*cur), GFP_KERNEL);
+	if (!cur)
+		return ERR_PTR(-ENOMEM);
+
+	cur->sw_msi_start = sw_msi_start;
+	cur->msi_addr = msi_addr;
+	cur->pgoff = max_pgoff;
+	cur->id = ictx->sw_msi_id++;
+	list_add_tail(&cur->sw_msi_item, &ictx->sw_msi_list);
+	return cur;
+}
+
+static int iommufd_sw_msi_install(struct iommufd_ctx *ictx,
+				  struct iommufd_hwpt_paging *hwpt_paging,
+				  struct iommufd_sw_msi_map *msi_map)
+{
+	unsigned long iova;
+
+	lockdep_assert_held(&ictx->sw_msi_lock);
+
+	iova = msi_map->sw_msi_start + msi_map->pgoff * PAGE_SIZE;
+	if (!test_bit(msi_map->id, hwpt_paging->present_sw_msi.bitmap)) {
+		int rc;
+
+		rc = iommu_map(hwpt_paging->common.domain, iova,
+			       msi_map->msi_addr, PAGE_SIZE,
+			       IOMMU_WRITE | IOMMU_READ | IOMMU_MMIO,
+			       GFP_KERNEL_ACCOUNT);
+		if (rc)
+			return rc;
+		__set_bit(msi_map->id, hwpt_paging->present_sw_msi.bitmap);
+	}
+	return 0;
+}
+
+/*
+ * Called by the irq code if the platform translates the MSI address through the
+ * IOMMU. msi_addr is the physical address of the MSI page. iommufd will
+ * allocate a fd global iova for the physical page that is the same on all
+ * domains and devices.
+ */
+#ifdef CONFIG_IRQ_MSI_IOMMU
+int iommufd_sw_msi(struct iommu_domain *domain, struct msi_desc *desc,
+		   phys_addr_t msi_addr)
+{
+	struct device *dev = msi_desc_to_dev(desc);
+	struct iommufd_hwpt_paging *hwpt_paging;
+	struct iommu_attach_handle *raw_handle;
+	struct iommufd_attach_handle *handle;
+	struct iommufd_sw_msi_map *msi_map;
+	struct iommufd_ctx *ictx;
+	unsigned long iova;
 	int rc;
 
 	/*
-	 * If the IOMMU driver gives a IOMMU_RESV_SW_MSI then it is asking us to
-	 * call iommu_get_msi_cookie() on its behalf. This is necessary to setup
-	 * the MSI window so iommu_dma_prepare_msi() can install pages into our
-	 * domain after request_irq(). If it is not done interrupts will not
-	 * work on this domain.
-	 *
-	 * FIXME: This is conceptually broken for iommufd since we want to allow
-	 * userspace to change the domains, eg switch from an identity IOAS to a
-	 * DMA IOAS. There is currently no way to create a MSI window that
-	 * matches what the IRQ layer actually expects in a newly created
-	 * domain.
+	 * It is safe to call iommu_attach_handle_get() here because the iommu
+	 * core code invokes this under the group mutex which also prevents any
+	 * change of the attach handle for the duration of this function.
 	 */
-	if (sw_msi_start != PHYS_ADDR_MAX && !hwpt_paging->msi_cookie) {
-		rc = iommu_get_msi_cookie(hwpt_paging->common.domain,
-					  sw_msi_start);
+	iommu_group_mutex_assert(dev);
+
+	raw_handle =
+		iommu_attach_handle_get(dev->iommu_group, IOMMU_NO_PASID, 0);
+	if (IS_ERR(raw_handle))
+		return 0;
+	hwpt_paging = find_hwpt_paging(domain->iommufd_hwpt);
+
+	handle = to_iommufd_handle(raw_handle);
+	/* No IOMMU_RESV_SW_MSI means no change to the msi_msg */
+	if (handle->idev->igroup->sw_msi_start == PHYS_ADDR_MAX)
+		return 0;
+
+	ictx = handle->idev->ictx;
+	guard(mutex)(&ictx->sw_msi_lock);
+	/*
+	 * The input msi_addr is the exact byte offset of the MSI doorbell, we
+	 * assume the caller has checked that it is contained with a MMIO region
+	 * that is secure to map at PAGE_SIZE.
+	 */
+	msi_map = iommufd_sw_msi_get_map(handle->idev->ictx,
+					 msi_addr & PAGE_MASK,
+					 handle->idev->igroup->sw_msi_start);
+	if (IS_ERR(msi_map))
+		return PTR_ERR(msi_map);
+
+	rc = iommufd_sw_msi_install(ictx, hwpt_paging, msi_map);
+	if (rc)
+		return rc;
+	__set_bit(msi_map->id, handle->idev->igroup->required_sw_msi.bitmap);
+
+	iova = msi_map->sw_msi_start + msi_map->pgoff * PAGE_SIZE;
+	msi_desc_set_iommu_msi_iova(desc, iova, PAGE_SHIFT);
+	return 0;
+}
+#endif
+
+static int iommufd_group_setup_msi(struct iommufd_group *igroup,
+				   struct iommufd_hwpt_paging *hwpt_paging)
+{
+	struct iommufd_ctx *ictx = igroup->ictx;
+	struct iommufd_sw_msi_map *cur;
+
+	if (igroup->sw_msi_start == PHYS_ADDR_MAX)
+		return 0;
+
+	/*
+	 * Install all the MSI pages the device has been using into the domain
+	 */
+	guard(mutex)(&ictx->sw_msi_lock);
+	list_for_each_entry(cur, &ictx->sw_msi_list, sw_msi_item) {
+		int rc;
+
+		if (cur->sw_msi_start != igroup->sw_msi_start ||
+		    !test_bit(cur->id, igroup->required_sw_msi.bitmap))
+			continue;
+
+		rc = iommufd_sw_msi_install(ictx, hwpt_paging, cur);
 		if (rc)
 			return rc;
-
-		/*
-		 * iommu_get_msi_cookie() can only be called once per domain,
-		 * it returns -EBUSY on later calls.
-		 */
-		hwpt_paging->msi_cookie = true;
 	}
 	return 0;
 }

drivers/iommu/iommufd/hw_pagetable.c

@@ -156,6 +156,7 @@ iommufd_hwpt_paging_alloc(struct iommufd_ctx *ictx, struct iommufd_ioas *ioas,
 			goto out_abort;
 		}
 	}
+	iommu_domain_set_sw_msi(hwpt->domain, iommufd_sw_msi);
 
 	/*
 	 * Set the coherency mode before we do iopt_table_add_domain() as some
@@ -251,6 +252,7 @@ iommufd_hwpt_nested_alloc(struct iommufd_ctx *ictx,
 		goto out_abort;
 	}
 	hwpt->domain->owner = ops;
+	iommu_domain_set_sw_msi(hwpt->domain, iommufd_sw_msi);
 
 	if (WARN_ON_ONCE(hwpt->domain->type != IOMMU_DOMAIN_NESTED)) {
 		rc = -EINVAL;
@@ -307,6 +309,7 @@ iommufd_viommu_alloc_hwpt_nested(struct iommufd_viommu *viommu, u32 flags,
 		goto out_abort;
 	}
 	hwpt->domain->owner = viommu->iommu_dev->ops;
+	iommu_domain_set_sw_msi(hwpt->domain, iommufd_sw_msi);
 
 	if (WARN_ON_ONCE(hwpt->domain->type != IOMMU_DOMAIN_NESTED)) {
 		rc = -EINVAL;

drivers/iommu/iommufd/iommufd_private.h

@@ -19,6 +19,22 @@ struct iommu_group;
 struct iommu_option;
 struct iommufd_device;
 
+struct iommufd_sw_msi_map {
+	struct list_head sw_msi_item;
+	phys_addr_t sw_msi_start;
+	phys_addr_t msi_addr;
+	unsigned int pgoff;
+	unsigned int id;
+};
+
+/* Bitmap of struct iommufd_sw_msi_map::id */
+struct iommufd_sw_msi_maps {
+	DECLARE_BITMAP(bitmap, 64);
+};
+
+int iommufd_sw_msi(struct iommu_domain *domain, struct msi_desc *desc,
+		   phys_addr_t msi_addr);
+
 struct iommufd_ctx {
 	struct file *file;
 	struct xarray objects;
@@ -26,6 +42,10 @@ struct iommufd_ctx {
 	wait_queue_head_t destroy_wait;
 	struct rw_semaphore ioas_creation_lock;
 
+	struct mutex sw_msi_lock;
+	struct list_head sw_msi_list;
+	unsigned int sw_msi_id;
+
 	u8 account_mode;
 	/* Compatibility with VFIO no iommu */
 	u8 no_iommu_mode;
@@ -283,10 +303,10 @@ struct iommufd_hwpt_paging {
 	struct iommufd_ioas *ioas;
 	bool auto_domain : 1;
 	bool enforce_cache_coherency : 1;
-	bool msi_cookie : 1;
 	bool nest_parent : 1;
 	/* Head at iommufd_ioas::hwpt_list */
 	struct list_head hwpt_item;
+	struct iommufd_sw_msi_maps present_sw_msi;
 };
 
 struct iommufd_hwpt_nested {
@@ -383,6 +403,7 @@ struct iommufd_group {
 	struct iommu_group *group;
 	struct iommufd_hw_pagetable *hwpt;
 	struct list_head device_list;
+	struct iommufd_sw_msi_maps required_sw_msi;
 	phys_addr_t sw_msi_start;
 };
 

drivers/iommu/iommufd/main.c

@@ -227,6 +227,8 @@ static int iommufd_fops_open(struct inode *inode, struct file *filp)
 	xa_init(&ictx->groups);
 	ictx->file = filp;
 	init_waitqueue_head(&ictx->destroy_wait);
+	mutex_init(&ictx->sw_msi_lock);
+	INIT_LIST_HEAD(&ictx->sw_msi_list);
 	filp->private_data = ictx;
 	return 0;
 }
@@ -234,6 +236,8 @@ static int iommufd_fops_open(struct inode *inode, struct file *filp)
 static int iommufd_fops_release(struct inode *inode, struct file *filp)
 {
 	struct iommufd_ctx *ictx = filp->private_data;
+	struct iommufd_sw_msi_map *next;
+	struct iommufd_sw_msi_map *cur;
 	struct iommufd_object *obj;
 
 	/*
@@ -262,6 +266,11 @@ static int iommufd_fops_release(struct inode *inode, struct file *filp)
 			break;
 	}
 	WARN_ON(!xa_empty(&ictx->groups));
+
+	mutex_destroy(&ictx->sw_msi_lock);
+	list_for_each_entry_safe(cur, next, &ictx->sw_msi_list, sw_msi_item)
+		kfree(cur);
+
 	kfree(ictx);
 	return 0;
 }