[RFC PATCH 01/13] iommufd: Support marking and tracking persistent iommufds

James Gowans
2024-09-16T11:31:44Z

Introduce a new iommufd option to mark an iommufd as persistent. For now
this allocates it a unique persistent ID from an xarray index and keeps
a reference to the domain.

This will be used so that at serialisation time the open iommufds can be
iterated through and serialised.
---
drivers/iommu/iommufd/iommufd_private.h | 1 +
drivers/iommu/iommufd/main.c | 47 +++++++++++++++++++++++++
include/uapi/linux/iommufd.h | 5 +++
3 files changed, 53 insertions(+)

diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
index 92efe30a8f0d..b23f7766066c 100644
--- a/drivers/iommu/iommufd/iommufd_private.h
+++ b/drivers/iommu/iommufd/iommufd_private.h
@@ -28,6 +28,7 @@ struct iommufd_ctx {
/* Compatibility with VFIO no iommu */
u8 no_iommu_mode;
struct iommufd_ioas *vfio_ioas;
+ unsigned long persistent_id;
};

/*
diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
index 83bbd7c5d160..6708ad629b1e 100644
--- a/drivers/iommu/iommufd/main.c
+++ b/drivers/iommu/iommufd/main.c
@@ -29,6 +29,8 @@ struct iommufd_object_ops {
static const struct iommufd_object_ops iommufd_object_ops[];
static struct miscdevice vfio_misc_dev;

+static DEFINE_XARRAY_ALLOC(persistent_iommufds);
+
struct iommufd_object *_iommufd_object_alloc(struct iommufd_ctx *ictx,
size_t size,
enum iommufd_object_type type)
@@ -287,10 +289,52 @@ static int iommufd_fops_release(struct inode *inode, struct file *filp)
break;
}
WARN_ON(!xa_empty(&ictx->groups));
+
+ rcu_read_lock();
+ if (ictx->persistent_id)
+ xa_erase(&persistent_iommufds, ictx->persistent_id);
+ rcu_read_unlock();
kfree(ictx);
return 0;
}

+static int iommufd_option_persistent(struct iommufd_ucmd *ucmd)
+{
+ unsigned int persistent_id;
+ int rc;
+ struct iommu_option *cmd = ucmd->cmd;
+ struct iommufd_ctx *ictx = ucmd->ictx;
+ struct xa_limit id_limit = XA_LIMIT(1, UINT_MAX);
+
+ if (cmd->op == IOMMU_OPTION_OP_GET) {
+ cmd->val64 = ictx->persistent_id;
+ return 0;
+ }
+
+ if (cmd->op == IOMMU_OPTION_OP_SET) {
+ /*
+ * iommufds can only be marked persistent before they
+ * have been used for DMA mappings. HWPTs must be known
+ * to be persistent at creation time.
+ */
+ if (!xa_empty(&ictx->objects)) {
+ pr_warn("iommufd can only be marked persistented when unused\n");
+ return -EFAULT;
+ }
+
+ rc = xa_alloc(&persistent_iommufds, &persistent_id, ictx, id_limit, GFP_KERNEL_ACCOUNT);
+ if (rc) {
+ pr_warn("Unable to keep track of iommufd object\n");
+ return rc;
+ }
+
+ ictx->persistent_id = persistent_id;
+ cmd->val64 = ictx->persistent_id;
+ return 0;
+ }
+ return -EOPNOTSUPP;
+}
+
static int iommufd_option(struct iommufd_ucmd *ucmd)
{
struct iommu_option *cmd = ucmd->cmd;
@@ -306,6 +350,9 @@ static int iommufd_option(struct iommufd_ucmd *ucmd)
case IOMMU_OPTION_HUGE_PAGES:
rc = iommufd_ioas_option(ucmd);
break;
+ case IOMMU_OPTION_PERSISTENT:
+ rc = iommufd_option_persistent(ucmd);
+ break;
default:
return -EOPNOTSUPP;
}
diff --git a/include/uapi/linux/iommufd.h b/include/uapi/linux/iommufd.h
index 4dde745cfb7e..7d8cb242e9b0 100644
--- a/include/uapi/linux/iommufd.h
+++ b/include/uapi/linux/iommufd.h
@@ -276,10 +276,15 @@ struct iommu_ioas_unmap {
* iommu mappings. Value 0 disables combining, everything is mapped to
* PAGE_SIZE. This can be useful for benchmarking. This is a per-IOAS
* option, the object_id must be the IOAS ID.
+ * @IOMMU_OPTION_PERSISTENT
+ * Value 1 sets this iommufd object as a persistent iommufd. Mappings will
+ * survive across kexec. The returned value is the persistent ID which can
+ * be used to restore the iommufd after kexec.
*/
enum iommufd_option {
IOMMU_OPTION_RLIMIT_MODE = 0,
IOMMU_OPTION_HUGE_PAGES = 1,
+ IOMMU_OPTION_PERSISTENT = 2,
};

/**
--
2.34.1