[PATCH v2 2/2] riscv: Define TASK_SIZE_MAX for __access_ok()

[Alexandre Ghiti]

On 27/03/2024 15:38, Samuel Holland wrote:
> TASK_SIZE_MAX should be set to a constant value, at least the largest
> valid userspace address under any runtime configuration. This optimizes
> the check in __access_ok(), which no longer needs to compute the runtime
> value of TASK_SIZE. The check does not need to be exact, as long as it
> accepts all valid userspace addresses and rejects all valid kernel
> addresses; well-behaved programs will never fail the access_ok() check.
>
> For RISC-V, which requires all virtual addresses to be sign extended,
> the optimal choice is LONG_MAX because it simplifies the limit
> comparison to a sign bit test.
>
> This removes about half of the references to pgtable_l[45]_enabled.
>
> Signed-off-by: Samuel Holland <samuel.holland at sifive.com>
> ---
>
> Changes in v2:
>   - Set TASK_SIZE_MAX to LONG_MAX to optimize the comparison
>   - Reword the commit message
>
>   arch/riscv/include/asm/pgtable.h | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index f5cc8bcc7f8d..762a85551764 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -870,6 +870,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
>    */
>   #ifdef CONFIG_64BIT
>   #define TASK_SIZE_64	(PGDIR_SIZE * PTRS_PER_PGD / 2)
> +#define TASK_SIZE_MAX	LONG_MAX
>   
>   #ifdef CONFIG_COMPAT
>   #define TASK_SIZE_32	(_AC(0x80000000, UL) - PAGE_SIZE)


You can add:

Reviewed-by: Alexandre Ghiti <alexghiti at rivosinc.com>

Thanks,

Alex