riscv: Extend sv39 linear mapping max size to 128G

This harmonizes all virtual addressing modes which can now all map
(PGDIR_SIZE * PTRS_PER_PGD) / 4 of physical memory.

The RISCV implementation of KASAN requires that the boundary between
shallow mappings are aligned on an 8G boundary. In this case we need
VMALLOC_START to be 8G aligned. So although we only need to move the
start of the linear mapping down by 4GiB to allow 128GiB to be mapped,
we actually move it down by 8GiB (creating a 4GiB hole between the
linear mapping and KASAN shadow space) to maintain the alignment
requirement.

Signed-off-by: Stuart Menefy <[email protected]>
Reviewed-by: Alexandre Ghiti <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: Stuart Menefy

Documentation/arch/riscv/vm-layout.rst

@@ -47,11 +47,12 @@ RISC-V Linux Kernel SV39
                                                               | Kernel-space virtual memory, shared between all processes:
   ____________________________________________________________|___________________________________________________________
                     |            |                  |         |
-   ffffffc6fea00000 | -228    GB | ffffffc6feffffff |    6 MB | fixmap
-   ffffffc6ff000000 | -228    GB | ffffffc6ffffffff |   16 MB | PCI io
-   ffffffc700000000 | -228    GB | ffffffc7ffffffff |    4 GB | vmemmap
-   ffffffc800000000 | -224    GB | ffffffd7ffffffff |   64 GB | vmalloc/ioremap space
-   ffffffd800000000 | -160    GB | fffffff6ffffffff |  124 GB | direct mapping of all physical memory
+   ffffffc4fea00000 | -236    GB | ffffffc4feffffff |    6 MB | fixmap
+   ffffffc4ff000000 | -236    GB | ffffffc4ffffffff |   16 MB | PCI io
+   ffffffc500000000 | -236    GB | ffffffc5ffffffff |    4 GB | vmemmap
+   ffffffc600000000 | -232    GB | ffffffd5ffffffff |   64 GB | vmalloc/ioremap space
+   ffffffd600000000 | -168    GB | fffffff5ffffffff |  128 GB | direct mapping of all physical memory
+                    |            |                  |         |
    fffffff700000000 |  -36    GB | fffffffeffffffff |   32 GB | kasan
   __________________|____________|__________________|_________|____________________________________________________________
                                                               |

arch/riscv/include/asm/page.h

@@ -37,7 +37,7 @@
  * define the PAGE_OFFSET value for SV48 and SV39.
  */
 #define PAGE_OFFSET_L4		_AC(0xffffaf8000000000, UL)
-#define PAGE_OFFSET_L3		_AC(0xffffffd800000000, UL)
+#define PAGE_OFFSET_L3		_AC(0xffffffd600000000, UL)
 #else
 #define PAGE_OFFSET		_AC(CONFIG_PAGE_OFFSET, UL)
 #endif /* CONFIG_64BIT */