iommufd: Add kAPI toward external drivers for kernel access

Kernel access is the mode that VFIO "mdevs" use. In this case there is no
struct device and no IOMMU connection. iommufd acts as a record keeper for
accesses and returns the actual struct pages back to the caller to use
however they need. eg with kmap or the DMA API.

Each caller must create a struct iommufd_access with
iommufd_access_create(), similar to how iommufd_device_bind() works. Using
this struct the caller can access blocks of IOVA using
iommufd_access_pin_pages() or iommufd_access_rw().

Callers must provide a callback that immediately unpins any IOVA being
used within a range. This happens if userspace unmaps the IOVA under the
pin.

The implementation forwards the access requests directly to the iopt
infrastructure that manages the iopt_pages_access.

Link: https://lore.kernel.org/r/14-v6-a196d26f289e+11787-iommufd_jgg@nvidia.com
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Yi Liu <yi.l.liu@intel.com>
Tested-by: Lixiao Yang <lixiao.yang@intel.com>
Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

1 files changed, 42 insertions, 1 deletions

diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
index 185dff3eb32f..46c481a26d79 100644
--- a/include/linux/iommufd.h
+++ b/include/linux/iommufd.h
@@ -9,10 +9,12 @@
 #include <linux/types.h>
 #include <linux/errno.h>
 #include <linux/err.h>
-#include <linux/device.h>
 
+struct device;
 struct iommufd_device;
+struct page;
 struct iommufd_ctx;
+struct iommufd_access;
 struct file;
 
 struct iommufd_device *iommufd_device_bind(struct iommufd_ctx *ictx,
@@ -22,6 +24,11 @@ void iommufd_device_unbind(struct iommufd_device *idev);
 int iommufd_device_attach(struct iommufd_device *idev, u32 *pt_id);
 void iommufd_device_detach(struct iommufd_device *idev);
 
+struct iommufd_access_ops {
+	u8 needs_pin_pages : 1;
+	void (*unmap)(void *data, unsigned long iova, unsigned long length);
+};
+
 enum {
 	IOMMUFD_ACCESS_RW_READ = 0,
 	IOMMUFD_ACCESS_RW_WRITE = 1 << 0,
@@ -29,11 +36,24 @@ enum {
 	IOMMUFD_ACCESS_RW_KTHREAD = 1 << 1,
 };
 
+struct iommufd_access *
+iommufd_access_create(struct iommufd_ctx *ictx, u32 ioas_id,
+		      const struct iommufd_access_ops *ops, void *data);
+void iommufd_access_destroy(struct iommufd_access *access);
+
 void iommufd_ctx_get(struct iommufd_ctx *ictx);
 
 #if IS_ENABLED(CONFIG_IOMMUFD)
 struct iommufd_ctx *iommufd_ctx_from_file(struct file *file);
 void iommufd_ctx_put(struct iommufd_ctx *ictx);
+
+int iommufd_access_pin_pages(struct iommufd_access *access, unsigned long iova,
+			     unsigned long length, struct page **out_pages,
+			     unsigned int flags);
+void iommufd_access_unpin_pages(struct iommufd_access *access,
+				unsigned long iova, unsigned long length);
+int iommufd_access_rw(struct iommufd_access *access, unsigned long iova,
+		      void *data, size_t len, unsigned int flags);
 #else /* !CONFIG_IOMMUFD */
 static inline struct iommufd_ctx *iommufd_ctx_from_file(struct file *file)
 {
@@ -43,5 +63,26 @@ static inline struct iommufd_ctx *iommufd_ctx_from_file(struct file *file)
 static inline void iommufd_ctx_put(struct iommufd_ctx *ictx)
 {
 }
+
+static inline int iommufd_access_pin_pages(struct iommufd_access *access,
+					   unsigned long iova,
+					   unsigned long length,
+					   struct page **out_pages,
+					   unsigned int flags)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline void iommufd_access_unpin_pages(struct iommufd_access *access,
+					      unsigned long iova,
+					      unsigned long length)
+{
+}
+
+static inline int iommufd_access_rw(struct iommufd_access *access, unsigned long iova,
+		      void *data, size_t len, unsigned int flags)
+{
+	return -EOPNOTSUPP;
+}
 #endif /* CONFIG_IOMMUFD */
 #endif