[RFC 12/20] iommu/iommufd: Add IOMMU_CHECK_EXTENSION

[Liu Yi L <yi.l.liu@intel.com>]

As aforementioned, userspace should check extension for what formats
can be specified when allocating an IOASID. This patch adds such
interface for userspace. In this RFC, iommufd reports EXT_MAP_TYPE1V2
support and no no-snoop support yet.

Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
---
 drivers/iommu/iommufd/iommufd.c |  7 +++++++
 include/uapi/linux/iommu.h      | 27 +++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/drivers/iommu/iommufd/iommufd.c b/drivers/iommu/iommufd/iommufd.c
index 4839f128b24a..e45d76359e34 100644
--- a/drivers/iommu/iommufd/iommufd.c
+++ b/drivers/iommu/iommufd/iommufd.c
@@ -306,6 +306,13 @@ static long iommufd_fops_unl_ioctl(struct file *filep,
 		return ret;
 
 	switch (cmd) {
+	case IOMMU_CHECK_EXTENSION:
+		switch (arg) {
+		case EXT_MAP_TYPE1V2:
+			return 1;
+		default:
+			return 0;
+		}
 	case IOMMU_DEVICE_GET_INFO:
 		ret = iommufd_get_device_info(ictx, arg);
 		break;
diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
index 5cbd300eb0ee..49731be71213 100644
--- a/include/uapi/linux/iommu.h
+++ b/include/uapi/linux/iommu.h
@@ -14,6 +14,33 @@
 #define IOMMU_TYPE	(';')
 #define IOMMU_BASE	100
 
+/*
+ * IOMMU_CHECK_EXTENSION - _IO(IOMMU_TYPE, IOMMU_BASE + 0)
+ *
+ * Check whether an uAPI extension is supported.
+ *
+ * It's unlikely that all planned capabilities in IOMMU fd will be ready
+ * in one breath. User should check which uAPI extension is supported
+ * according to its intended usage.
+ *
+ * A rough list of possible extensions may include:
+ *
+ *	- EXT_MAP_TYPE1V2 for vfio type1v2 map semantics;
+ *	- EXT_DMA_NO_SNOOP for no-snoop DMA support;
+ *	- EXT_MAP_NEWTYPE for an enhanced map semantics;
+ *	- EXT_MULTIDEV_GROUP for 1:N iommu group;
+ *	- EXT_IOASID_NESTING for what the name stands;
+ *	- EXT_USER_PAGE_TABLE for user managed page table;
+ *	- EXT_USER_PASID_TABLE for user managed PASID table;
+ *	- EXT_DIRTY_TRACKING for tracking pages dirtied by DMA;
+ *	- ...
+ *
+ * Return: 0 if not supported, 1 if supported.
+ */
+#define EXT_MAP_TYPE1V2		1
+#define EXT_DMA_NO_SNOOP	2
+#define IOMMU_CHECK_EXTENSION	_IO(IOMMU_TYPE, IOMMU_BASE + 0)
+
 /*
  * IOMMU_DEVICE_GET_INFO - _IOR(IOMMU_TYPE, IOMMU_BASE + 1,
  *				struct iommu_device_info)
-- 
2.25.1