powerpc/64e: Reorganise virtual memory

Reduce the size of IO map in order to leave the last
quarter of virtual MAP for KASAN shadow mapping.

This gives the following layout.

   +------------------------+  Kernel virtual map end (0xc000200000000000)
   |                        |
   |    16TB (unused)       |
   |                        |
   +------------------------+  Kernel IO map end
   |                        |
   |    16TB of IO map      |
   |                        |
   +------------------------+  Kernel IO map start
   |                        |
   |    16TB of vmemmap     |
   |                        |
   +------------------------+  Kernel vmemmap start
   |                        |
   |    16TB of vmap        |
   |                        |
   +------------------------+  Kernel virt start (0xc000100000000000)
   |                        |
   |    64TB of linear mem  |
   |                        |
   +------------------------+  Kernel linear (0xc.....)

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/54ef01673bf14228106afd629f795c83acb9a00c.1656427701.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/nohash/64/pgtable.h

@@ -38,23 +38,24 @@
 #define VMALLOC_END	(VMALLOC_START + VMALLOC_SIZE)
 
 /*
- * The second half of the kernel virtual space is used for IO mappings,
+ * The third quarter of the kernel virtual space is used for IO mappings,
  * it's itself carved into the PIO region (ISA and PHB IO space) and
  * the ioremap space
  *
  *  ISA_IO_BASE = KERN_IO_START, 64K reserved area
  *  PHB_IO_BASE = ISA_IO_BASE + 64K to ISA_IO_BASE + 2G, PHB IO spaces
- * IOREMAP_BASE = ISA_IO_BASE + 2G to VMALLOC_START + PGTABLE_RANGE
+ * IOREMAP_BASE = ISA_IO_BASE + 2G to KERN_IO_START + KERN_IO_SIZE
  */
 #define KERN_IO_START	(KERN_VIRT_START + (KERN_VIRT_SIZE >> 1))
+#define KERN_IO_SIZE	(KERN_VIRT_SIZE >> 2)
 #define FULL_IO_SIZE	0x80000000ul
 #define  ISA_IO_BASE	(KERN_IO_START)
 #define  ISA_IO_END	(KERN_IO_START + 0x10000ul)
 #define  PHB_IO_BASE	(ISA_IO_END)
 #define  PHB_IO_END	(KERN_IO_START + FULL_IO_SIZE)
 #define IOREMAP_BASE	(PHB_IO_END)
 #define IOREMAP_START	(ioremap_bot)
-#define IOREMAP_END	(KERN_VIRT_START + KERN_VIRT_SIZE - FIXADDR_SIZE)
+#define IOREMAP_END	(KERN_IO_START + KERN_IO_SIZE - FIXADDR_SIZE)
 #define FIXADDR_SIZE	SZ_32M
 
 /*