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

Liu Yi L
2021-09-19T06:43:26Z

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