RISC-V: Introduce sv48 support without relocatable kernel

This patchset allows to have a single kernel for sv39 and sv48 without
being relocatable.

The idea comes from Arnd Bergmann who suggested to do the same as x86,
that is mapping the kernel to the end of the address space, which allows
the kernel to be linked at the same address for both sv39 and sv48 and
then does not require to be relocated at runtime.

This implements sv48 support at runtime. The kernel will try to boot
with 4-level page table and will fallback to 3-level if the HW does not
support it. Folding the 4th level into a 3-level page table has almost
no cost at runtime.

Note that kasan region had to be moved to the end of the address space
since its location must be known at compile-time and then be valid for
both sv39 and sv48 (and sv57 that is coming).

* riscv-sv48-v3:
  riscv: Explicit comment about user virtual address space size
  riscv: Use pgtable_l4_enabled to output mmu_type in cpuinfo
  riscv: Implement sv48 support
  asm-generic: Prepare for riscv use of pud_alloc_one and pud_free
  riscv: Allow to dynamically define VA_BITS
  riscv: Introduce functions to switch pt_ops
  riscv: Split early kasan mapping to prepare sv48 introduction
  riscv: Move KASAN mapping next to the kernel mapping
  riscv: Get rid of MAXPHYSMEM configs

Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

2 files changed, 14 insertions, 12 deletions

diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
index f13b2c9ea912..ad0a7e9f828b 100644
--- a/arch/riscv/kernel/cpu.c
+++ b/arch/riscv/kernel/cpu.c
@@ -7,6 +7,7 @@
 #include <linux/seq_file.h>
 #include <linux/of.h>
 #include <asm/smp.h>
+#include <asm/pgtable.h>
 
 /*
  * Returns the hart ID of the given device tree node, or -ENODEV if the node
@@ -71,18 +72,19 @@ static void print_isa(struct seq_file *f, const char *isa)
 	seq_puts(f, "\n");
 }
 
-static void print_mmu(struct seq_file *f, const char *mmu_type)
+static void print_mmu(struct seq_file *f)
 {
+	char sv_type[16];
+
 #if defined(CONFIG_32BIT)
-	if (strcmp(mmu_type, "riscv,sv32") != 0)
-		return;
+	strncpy(sv_type, "sv32", 5);
 #elif defined(CONFIG_64BIT)
-	if (strcmp(mmu_type, "riscv,sv39") != 0 &&
-	    strcmp(mmu_type, "riscv,sv48") != 0)
-		return;
+	if (pgtable_l4_enabled)
+		strncpy(sv_type, "sv48", 5);
+	else
+		strncpy(sv_type, "sv39", 5);
 #endif
-
-	seq_printf(f, "mmu\t\t: %s\n", mmu_type+6);
+	seq_printf(f, "mmu\t\t: %s\n", sv_type);
 }
 
 static void *c_start(struct seq_file *m, loff_t *pos)
@@ -107,14 +109,13 @@ static int c_show(struct seq_file *m, void *v)
 {
 	unsigned long cpu_id = (unsigned long)v - 1;
 	struct device_node *node = of_get_cpu_node(cpu_id, NULL);
-	const char *compat, *isa, *mmu;
+	const char *compat, *isa;
 
 	seq_printf(m, "processor\t: %lu\n", cpu_id);
 	seq_printf(m, "hart\t\t: %lu\n", cpuid_to_hartid_map(cpu_id));
 	if (!of_property_read_string(node, "riscv,isa", &isa))
 		print_isa(m, isa);
-	if (!of_property_read_string(node, "mmu-type", &mmu))
-		print_mmu(m, mmu);
+	print_mmu(m);
 	if (!of_property_read_string(node, "compatible", &compat)
 	    && strcmp(compat, "riscv"))
 		seq_printf(m, "uarch\t\t: %s\n", compat);
diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index 604d60292dd8..db4be6a7e392 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -105,7 +105,8 @@ relocate:
 
 	/* Compute satp for kernel page tables, but don't load it yet */
 	srl a2, a0, PAGE_SHIFT
-	li a1, SATP_MODE
+	la a1, satp_mode
+	REG_L a1, 0(a1)
 	or a2, a2, a1
 
 	/*