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 <alexandre.ghiti@xxxxxxxxxxxxx> Reviewed-by: Anup Patel <anup@xxxxxxxxxxxxxx> Reviewed-by: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx> --- arch/riscv/include/asm/pgtable.h | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h index e1c74ef4ead2..fe1701329237 100644 --- a/arch/riscv/include/asm/pgtable.h +++ b/arch/riscv/include/asm/pgtable.h @@ -677,6 +677,15 @@ static inline pmd_t pmdp_establish(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 + * 63–48 all equal to bit 47, or else a page-fault exception will occur." */ #ifdef CONFIG_64BIT #define TASK_SIZE (PGDIR_SIZE * PTRS_PER_PGD / 2) -- 2.32.0
