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diff --git a/sys/riscv/include/vmparam.h b/sys/riscv/include/vmparam.h
--- a/sys/riscv/include/vmparam.h
+++ b/sys/riscv/include/vmparam.h
@@ -116,14 +116,19 @@
* Address space layout.
*
* RISC-V implements multiple paging modes with different virtual address space
- * sizes: SV32, SV39 and SV48. SV39 permits a virtual address space size of
- * 512GB and uses a three-level page table. Since this is large enough for most
- * purposes, we currently use SV39 for both userland and the kernel, avoiding
- * the extra translation step required by SV48.
+ * sizes: SV32, SV39, SV48 and SV57. Only SV39 and SV48 are supported by
+ * FreeBSD. SV39 provides a 512GB virtual address space and uses three-level
+ * page tables, while SV48 provides a 256TB virtual address space and uses
+ * four-level page tables. 64-bit RISC-V implementations are required to provide
+ * at least SV39 mode; locore initially enables SV39 mode while bootstrapping
+ * page tables, and pmap_bootstrap() optionally switches to SV48 mode.
*
* The address space is split into two regions at each end of the 64-bit address
- * space:
+ * space; the lower region is for use by user mode software, while the upper
+ * region is used for various kernel maps. The kernel map layout in SV48 mode
+ * is currently identical to that used in SV39 mode.
*
+ * SV39 memory map:
* 0x0000000000000000 - 0x0000003fffffffff 256GB user map
* 0x0000004000000000 - 0xffffffbfffffffff unmappable
* 0xffffffc000000000 - 0xffffffc7ffffffff 32GB kernel map
@@ -131,6 +136,15 @@
* 0xffffffd000000000 - 0xffffffefffffffff 128GB direct map
* 0xfffffff000000000 - 0xffffffffffffffff 64GB unused
*
+ * SV48 memory map:
+ * 0x0000000000000000 - 0x00007fffffffffff 128TB user map
+ * 0x0000800000000000 - 0xffff7fffffffffff unmappable
+ * 0xffff800000000000 - 0xffffffc7ffffffff 127.75TB hole
+ * 0xffffffc000000000 - 0xffffffc7ffffffff 32GB kernel map
+ * 0xffffffc800000000 - 0xffffffcfffffffff 32GB unused
+ * 0xffffffd000000000 - 0xffffffefffffffff 128GB direct map
+ * 0xfffffff000000000 - 0xffffffffffffffff 64GB unused
+ *
* The kernel is loaded at the beginning of the kernel map.
*
* We define some interesting address constants:
@@ -180,9 +194,9 @@
((va) - DMAP_MIN_ADDRESS) + dmap_phys_base; \
})
-#define VM_MIN_USER_ADDRESS_SV39 (0x0000000000000000UL)
+#define VM_MIN_USER_ADDRESS (0x0000000000000000UL)
#define VM_MAX_USER_ADDRESS_SV39 (0x0000004000000000UL)
-#define VM_MIN_USER_ADDRESS VM_MIN_USER_ADDRESS_SV39
+#define VM_MAX_USER_ADDRESS_SV48 (0x0000800000000000UL)
#define VM_MAX_USER_ADDRESS VM_MAX_USER_ADDRESS_SV39
#define VM_MINUSER_ADDRESS (VM_MIN_USER_ADDRESS)
@@ -194,9 +208,13 @@
#define KERNBASE (VM_MIN_KERNEL_ADDRESS)
#define SHAREDPAGE_SV39 (VM_MAX_USER_ADDRESS_SV39 - PAGE_SIZE)
+#define SHAREDPAGE_SV48 (VM_MAX_USER_ADDRESS_SV48 - PAGE_SIZE)
#define SHAREDPAGE SHAREDPAGE_SV39
-#define USRSTACK SHAREDPAGE_SV39
+#define USRSTACK_SV39 SHAREDPAGE_SV39
+#define USRSTACK_SV48 SHAREDPAGE_SV48
+#define USRSTACK USRSTACK_SV39
#define PS_STRINGS_SV39 (USRSTACK_SV39 - sizeof(struct ps_strings))
+#define PS_STRINGS_SV48 (USRSTACK_SV48 - sizeof(struct ps_strings))
#define VM_EARLY_DTB_ADDRESS (VM_MAX_KERNEL_ADDRESS - (2 * L2_SIZE))

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