Unverified Commit c774de22 authored by Alexandre Ghiti's avatar Alexandre Ghiti Committed by Palmer Dabbelt
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riscv: Explicit comment about user virtual address space size 



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: default avatarAlexandre Ghiti <alexandre.ghiti@canonical.com>
Reviewed-by: default avatarAnup Patel <anup@brainfault.org>
Reviewed-by: default avatarPalmer Dabbelt <palmerdabbelt@google.com>
Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent 73c7c8f6

arch/riscv/include/asm/pgtable.h

+9 −0
Original line number Diff line number Diff line
@@ -685,6 +685,15 @@ 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)