Re: [PATCH v5 16/16] target/riscv: Compute mstatus.sd on demand

[Alistair Francis]

On Wed, Oct 20, 2021 at 2:52 AM Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> The position of this read-only field is dependent on the
> current cpu width.  Rather than having to compute that
> difference in many places, compute it only on read.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/cpu_helper.c |  3 +--
>  target/riscv/csr.c        | 37 ++++++++++++++++++++++---------------
>  target/riscv/translate.c  |  5 ++---
>  3 files changed, 25 insertions(+), 20 deletions(-)
>
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index 429afd1f48..0d1132f39d 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -185,10 +185,9 @@ bool riscv_cpu_fp_enabled(CPURISCVState *env)
>
>  void riscv_cpu_swap_hypervisor_regs(CPURISCVState *env)
>  {
> -    uint64_t sd = riscv_cpu_mxl(env) == MXL_RV32 ? MSTATUS32_SD : 
> MSTATUS64_SD;
>      uint64_t mstatus_mask = MSTATUS_MXR | MSTATUS_SUM | MSTATUS_FS |
>                              MSTATUS_SPP | MSTATUS_SPIE | MSTATUS_SIE |
> -                            MSTATUS64_UXL | sd;
> +                            MSTATUS64_UXL;
>      bool current_virt = riscv_cpu_virt_enabled(env);
>
>      g_assert(riscv_has_ext(env, RVH));
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index c4a479ddd2..69e4d65fcd 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -477,10 +477,28 @@ static RISCVException read_mhartid(CPURISCVState *env, 
> int csrno,
>  }
>
>  /* Machine Trap Setup */
> +
> +/* We do not store SD explicitly, only compute it on demand. */
> +static uint64_t add_status_sd(RISCVMXL xl, uint64_t status)
> +{
> +    if ((status & MSTATUS_FS) == MSTATUS_FS ||
> +        (status & MSTATUS_XS) == MSTATUS_XS) {
> +        switch (xl) {
> +        case MXL_RV32:
> +            return status | MSTATUS32_SD;
> +        case MXL_RV64:
> +            return status | MSTATUS64_SD;
> +        default:
> +            g_assert_not_reached();
> +        }
> +    }
> +    return status;
> +}
> +
>  static RISCVException read_mstatus(CPURISCVState *env, int csrno,
>                                     target_ulong *val)
>  {
> -    *val = env->mstatus;
> +    *val = add_status_sd(riscv_cpu_mxl(env), env->mstatus);
>      return RISCV_EXCP_NONE;
>  }
>
> @@ -498,7 +516,6 @@ static RISCVException write_mstatus(CPURISCVState *env, 
> int csrno,
>  {
>      uint64_t mstatus = env->mstatus;
>      uint64_t mask = 0;
> -    int dirty;
>
>      /* flush tlb on mstatus fields that affect VM */
>      if ((val ^ mstatus) & (MSTATUS_MXR | MSTATUS_MPP | MSTATUS_MPV |
> @@ -520,12 +537,7 @@ static RISCVException write_mstatus(CPURISCVState *env, 
> int csrno,
>
>      mstatus = (mstatus & ~mask) | (val & mask);
>
> -    dirty = ((mstatus & MSTATUS_FS) == MSTATUS_FS) |
> -            ((mstatus & MSTATUS_XS) == MSTATUS_XS);
> -    if (riscv_cpu_mxl(env) == MXL_RV32) {
> -        mstatus = set_field(mstatus, MSTATUS32_SD, dirty);
> -    } else {
> -        mstatus = set_field(mstatus, MSTATUS64_SD, dirty);
> +    if (riscv_cpu_mxl(env) == MXL_RV64) {
>          /* SXL and UXL fields are for now read only */
>          mstatus = set_field(mstatus, MSTATUS64_SXL, MXL_RV64);
>          mstatus = set_field(mstatus, MSTATUS64_UXL, MXL_RV64);
> @@ -798,13 +810,8 @@ static RISCVException read_sstatus(CPURISCVState *env, 
> int csrno,
>  {
>      target_ulong mask = (sstatus_v1_10_mask);
>
> -    if (riscv_cpu_mxl(env) == MXL_RV32) {
> -        mask |= SSTATUS32_SD;
> -    } else {
> -        mask |= SSTATUS64_SD;
> -    }
> -
> -    *val = env->mstatus & mask;
> +    /* TODO: Use SXL not MXL. */
> +    *val = add_status_sd(riscv_cpu_mxl(env), env->mstatus & mask);
>      return RISCV_EXCP_NONE;
>  }
>
> diff --git a/target/riscv/translate.c b/target/riscv/translate.c
> index de013fbf9b..35245aafa7 100644
> --- a/target/riscv/translate.c
> +++ b/target/riscv/translate.c
> @@ -280,7 +280,6 @@ static void gen_jal(DisasContext *ctx, int rd, 
> target_ulong imm)
>  static void mark_fs_dirty(DisasContext *ctx)
>  {
>      TCGv tmp;
> -    target_ulong sd = get_xl(ctx) == MXL_RV32 ? MSTATUS32_SD : MSTATUS64_SD;
>
>      if (ctx->mstatus_fs != MSTATUS_FS) {
>          /* Remember the state change for the rest of the TB. */
> @@ -288,7 +287,7 @@ static void mark_fs_dirty(DisasContext *ctx)
>
>          tmp = tcg_temp_new();
>          tcg_gen_ld_tl(tmp, cpu_env, offsetof(CPURISCVState, mstatus));
> -        tcg_gen_ori_tl(tmp, tmp, MSTATUS_FS | sd);
> +        tcg_gen_ori_tl(tmp, tmp, MSTATUS_FS);
>          tcg_gen_st_tl(tmp, cpu_env, offsetof(CPURISCVState, mstatus));
>          tcg_temp_free(tmp);
>      }
> @@ -299,7 +298,7 @@ static void mark_fs_dirty(DisasContext *ctx)
>
>          tmp = tcg_temp_new();
>          tcg_gen_ld_tl(tmp, cpu_env, offsetof(CPURISCVState, mstatus_hs));
> -        tcg_gen_ori_tl(tmp, tmp, MSTATUS_FS | sd);
> +        tcg_gen_ori_tl(tmp, tmp, MSTATUS_FS);
>          tcg_gen_st_tl(tmp, cpu_env, offsetof(CPURISCVState, mstatus_hs));
>          tcg_temp_free(tmp);
>      }
> --
> 2.25.1
>
>