Re: [PATCH V3 1/4] riscv: mm: Fixup compat mode boot failure

Leonardo Bras
2023-12-23T02:58:10Z

On Fri, Dec 22, 2023 at 06:57:00AM -0500, guoren@kernel.org wrote:
> From: Guo Ren <guoren@linux.alibaba.com>
>
> In COMPAT mode, the STACK_TOP is DEFAULT_MAP_WINDOW (0x80000000), but
> the TASK_SIZE is 0x7fff000. When the user stack is upon 0x7fff000, it
> will cause a user segment fault. Sometimes, it would cause boot
> failure when the whole rootfs is rv32.
>
> Freeing unused kernel image (initmem) memory: 2236K
> Run /sbin/init as init process
> Starting init: /sbin/init exists but couldn't execute it (error -14)
> Run /etc/init as init process
> ...
>
> Increase the TASK_SIZE to cover STACK_TOP.
>
> Cc: stable@vger.kernel.org
> Fixes: add2cc6b6515 ("RISC-V: mm: Restrict address space for sv39,sv48,sv57")
> Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@kernel.org>
> ---
> arch/riscv/include/asm/pgtable.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index ab00235b018f..74ffb2178f54 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -881,7 +881,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
> #define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
>
> #ifdef CONFIG_COMPAT
> -#define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
> +#define TASK_SIZE_32 (_AC(0x80000000, UL))
> #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
> TASK_SIZE_32 : TASK_SIZE_64)
> #else
> --
> 2.40.1
>

I am not really involved in the issue this is solving, so I have no
technical opinion on the solution.

IIUC there should always be (TASK_SIZE >= STACK_TOP), so by itself this
is fixing an issue.

I have reviewed the code and it does exactly as stated into the commit
message, so FWIW:
Reviewed-by: Leonardo Bras <leobras@redhat.com>