Re: [PATCH v7 3/5] target/riscv: add support for svnapot extension

[Alistair Francis]

On Fri, Jan 28, 2022 at 6:57 PM Weiwei Li <liweiwei@iscas.ac.cn> wrote:
>
> - add PTE_N bit
> - add PTE_N bit check for inner PTE
> - update address translation to support 64KiB continuous region (napot_bits = 
> 4)
>
> Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
> Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
> Reviewed-by: Anup Patel <anup@brainfault.org>
> ---
>  target/riscv/cpu.c        |  2 ++
>  target/riscv/cpu_bits.h   |  1 +
>  target/riscv/cpu_helper.c | 17 ++++++++++++++---
>  3 files changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 1cb0436187..8752fa1544 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -729,6 +729,8 @@ static Property riscv_cpu_properties[] = {
>      DEFINE_PROP_UINT16("vlen", RISCVCPU, cfg.vlen, 128),
>      DEFINE_PROP_UINT16("elen", RISCVCPU, cfg.elen, 64),
>
> +    DEFINE_PROP_BOOL("svnapot", RISCVCPU, cfg.ext_svnapot, false),
> +
>      DEFINE_PROP_BOOL("zba", RISCVCPU, cfg.ext_zba, true),
>      DEFINE_PROP_BOOL("zbb", RISCVCPU, cfg.ext_zbb, true),
>      DEFINE_PROP_BOOL("zbc", RISCVCPU, cfg.ext_zbc, true),
> diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h
> index 6ea3944423..f6ff1c5012 100644
> --- a/target/riscv/cpu_bits.h
> +++ b/target/riscv/cpu_bits.h
> @@ -489,6 +489,7 @@ typedef enum {
>  #define PTE_A               0x040 /* Accessed */
>  #define PTE_D               0x080 /* Dirty */
>  #define PTE_SOFT            0x300 /* Reserved for Software */
> +#define PTE_N               0x8000000000000000 /* NAPOT translation */

This should be 0x8000000000000000ULL to avoid casting

>
>  /* Page table PPN shift amount */
>  #define PTE_PPN_SHIFT       10
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index b820166dc5..6262d157e2 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -641,7 +641,7 @@ restart:
>              return TRANSLATE_FAIL;
>          } else if (!(pte & (PTE_R | PTE_W | PTE_X))) {
>              /* Inner PTE, continue walking */
> -            if (pte & (PTE_D | PTE_A | PTE_U)) {
> +            if (pte & (target_ulong)(PTE_D | PTE_A | PTE_U | PTE_N)) {
>                  return TRANSLATE_FAIL;
>              }
>              base = ppn << PGSHIFT;
> @@ -717,8 +717,19 @@ restart:
>              /* for superpage mappings, make a fake leaf PTE for the TLB's
>                 benefit. */
>              target_ulong vpn = addr >> PGSHIFT;
> -            *physical = ((ppn | (vpn & ((1L << ptshift) - 1))) << PGSHIFT) |
> -                        (addr & ~TARGET_PAGE_MASK);
> +
> +            int napot_bits = 0;
> +            if (cpu->cfg.ext_svnapot && (pte & (target_ulong)PTE_N)) {
> +                napot_bits = ctzl(ppn) + 1;
> +                if ((i != (levels - 1)) || (napot_bits != 4)) {
> +                    return TRANSLATE_FAIL;
> +                }
> +            }
> +
> +            *physical = (((ppn & ~(((target_ulong)1 << napot_bits) - 1)) |

It might be clearer to create the mask as a variable, there are a lot
of brackets here :)

Alistair

> +                          (vpn & (((target_ulong)1 << napot_bits) - 1)) |
> +                          (vpn & (((target_ulong)1 << ptshift) - 1))
> +                        ) << PGSHIFT) | (addr & ~TARGET_PAGE_MASK);
>
>              /* set permissions on the TLB entry */
>              if ((pte & PTE_R) || ((pte & PTE_X) && mxr)) {
> --
> 2.17.1
>
>