iommu/vt-d: Extend dmar_domain to support nested domain

The nested domain fields are exclusive to those that used for a DMA
remapping domain. Use union to avoid memory waste.

Link: https://lore.kernel.org/r/20231026044216.64964-3-yi.l.liu@intel.com
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Author: LuBaolu

drivers/iommu/intel/iommu.h

@@ -25,6 +25,7 @@
 
 #include <asm/cacheflush.h>
 #include <asm/iommu.h>
+#include <uapi/linux/iommufd.h>
 
 /*
  * VT-d hardware uses 4KiB page size regardless of host page size.
@@ -605,15 +606,38 @@ struct dmar_domain {
 	struct list_head devices;	/* all devices' list */
 	struct list_head dev_pasids;	/* all attached pasids */
 
-	struct dma_pte	*pgd;		/* virtual address */
-	int		gaw;		/* max guest address width */
-
-	/* adjusted guest address width, 0 is level 2 30-bit */
-	int		agaw;
 	int		iommu_superpage;/* Level of superpages supported:
 					   0 == 4KiB (no superpages), 1 == 2MiB,
 					   2 == 1GiB, 3 == 512GiB, 4 == 1TiB */
-	u64		max_addr;	/* maximum mapped address */
+	union {
+		/* DMA remapping domain */
+		struct {
+			/* virtual address */
+			struct dma_pte	*pgd;
+			/* max guest address width */
+			int		gaw;
+			/*
+			 * adjusted guest address width:
+			 *   0: level 2 30-bit
+			 *   1: level 3 39-bit
+			 *   2: level 4 48-bit
+			 *   3: level 5 57-bit
+			 */
+			int		agaw;
+			/* maximum mapped address */
+			u64		max_addr;
+		};
+
+		/* Nested user domain */
+		struct {
+			/* parent page table which the user domain is nested on */
+			struct dmar_domain *s2_domain;
+			/* user page table pointer (in GPA) */
+			unsigned long s1_pgtbl;
+			/* page table attributes */
+			struct iommu_hwpt_vtd_s1 s1_cfg;
+		};
+	};
 
 	struct iommu_domain domain;	/* generic domain data structure for
 					   iommu core */