Messages in this thread Patch in this message | | | From | Alexandre Ghiti <> | Subject | [RFC PATCH 7/7] riscv: Explicit comment about user virtual address space size | Date | Sun, 22 Mar 2020 07:00:28 -0400 |
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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@ghiti.fr> --- 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 06361db3f486..be117a0b4ea1 100644 --- a/arch/riscv/include/asm/pgtable.h +++ b/arch/riscv/include/asm/pgtable.h @@ -456,8 +456,15 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma, #define FIXADDR_START (FIXADDR_TOP - FIXADDR_SIZE) /* - * 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) -- 2.20.1
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