[PATCH 8/8] riscv: Explicit comment about user virtual address space size
From: Alexandre Ghiti
Date: Sun May 24 2020 - 05:18:29 EST
Define precisely the size of the user accessible virtual space size
for sv32/39/48 mmu types and explain why the whole virtual address
space is split into 2 equal chunks between kernel and user space.
Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
Reviewed-by: Anup Patel <anup@xxxxxxxxxxxxxx>
Reviewed-by: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>
arch/riscv/include/asm/pgtable.h | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index b8a8ba69d0a2..0c7d07f614b3 100644
@@ -481,8 +481,15 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
- * Task size is 0x4000000000 for RV64 or 0x9fc00000 for RV32.
- * Note that PGDIR_SIZE must evenly divide TASK_SIZE.
+ * Task size is:
+ * - 0x9fc00000 (~2.5GB) for RV32.
+ * - 0x4000000000 ( 256GB) for RV64 using SV39 mmu
+ * - 0x800000000000 ( 128TB) for RV64 using SV48 mmu
+ * Note that PGDIR_SIZE must evenly divide TASK_SIZE since "RISC-V
+ * Instruction Set Manual Volume II: Privileged Architecture" states that
+ * "load and store effective addresses, which are 64bits, must have bits
+ * 63â48 all equal to bit 47, or else a page-fault exception will occur."
#define TASK_SIZE (PGDIR_SIZE * PTRS_PER_PGD / 2)