Re: [PATCH 2/2] target/riscv: remove force HS exception

[Alistair Francis]

On Thu, Jun 3, 2021 at 5:12 AM Jose Martins <josemartins90@gmail.com> wrote:
>
> There is no need to "force an hs exception" as the current privilege
> level, the state of the global ie and of the delegation registers should
> be enough to route the interrupt to the appropriate privilege level in
> riscv_cpu_do_interrupt. The is true for both asynchronous and
> synchronous exceptions, specifically, guest page faults which must be
> hardwired to zero hedeleg. As such the hs_force_except mechanism can be
> removed.
>
> Signed-off-by: Jose Martins <josemartins90@gmail.com>

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

Alistair

> ---
>  target/riscv/cpu.h        |  2 --
>  target/riscv/cpu_bits.h   |  6 ------
>  target/riscv/cpu_helper.c | 26 +-------------------------
>  3 files changed, 1 insertion(+), 33 deletions(-)
>
> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index 0a33d387ba..a30a64241a 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -337,8 +337,6 @@ bool riscv_cpu_exec_interrupt(CPUState *cs, int 
> interrupt_request);
>  bool riscv_cpu_fp_enabled(CPURISCVState *env);
>  bool riscv_cpu_virt_enabled(CPURISCVState *env);
>  void riscv_cpu_set_virt_enabled(CPURISCVState *env, bool enable);
> -bool riscv_cpu_force_hs_excep_enabled(CPURISCVState *env);
> -void riscv_cpu_set_force_hs_excep(CPURISCVState *env, bool enable);
>  bool riscv_cpu_two_stage_lookup(int mmu_idx);
>  int riscv_cpu_mmu_index(CPURISCVState *env, bool ifetch);
>  hwaddr riscv_cpu_get_phys_page_debug(CPUState *cpu, vaddr addr);
> diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h
> index caf4599207..7322f54157 100644
> --- a/target/riscv/cpu_bits.h
> +++ b/target/riscv/cpu_bits.h
> @@ -462,12 +462,6 @@
>
>  /* Virtulisation Register Fields */
>  #define VIRT_ONOFF          1
> -/* This is used to save state for when we take an exception. If this is set
> - * that means that we want to force a HS level exception (no matter what the
> - * delegation is set to). This will occur for things such as a second level
> - * page table fault.
> - */
> -#define FORCE_HS_EXCEP      2
>
>  /* RV32 satp CSR field masks */
>  #define SATP32_MODE         0x80000000
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index 592d4642be..babe3d844b 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -178,24 +178,6 @@ void riscv_cpu_set_virt_enabled(CPURISCVState *env, bool 
> enable)
>      env->virt = set_field(env->virt, VIRT_ONOFF, enable);
>  }
>
> -bool riscv_cpu_force_hs_excep_enabled(CPURISCVState *env)
> -{
> -    if (!riscv_has_ext(env, RVH)) {
> -        return false;
> -    }
> -
> -    return get_field(env->virt, FORCE_HS_EXCEP);
> -}
> -
> -void riscv_cpu_set_force_hs_excep(CPURISCVState *env, bool enable)
> -{
> -    if (!riscv_has_ext(env, RVH)) {
> -        return;
> -    }
> -
> -    env->virt = set_field(env->virt, FORCE_HS_EXCEP, enable);
> -}
> -
>  bool riscv_cpu_two_stage_lookup(int mmu_idx)
>  {
>      return mmu_idx & TB_FLAGS_PRIV_HYP_ACCESS_MASK;
> @@ -884,7 +866,6 @@ void riscv_cpu_do_interrupt(CPUState *cs)
>
>      RISCVCPU *cpu = RISCV_CPU(cs);
>      CPURISCVState *env = &cpu->env;
> -    bool force_hs_execp = riscv_cpu_force_hs_excep_enabled(env);
>      uint64_t s;
>
>      /* cs->exception is 32-bits wide unlike mcause which is XLEN-bits wide
> @@ -913,8 +894,6 @@ void riscv_cpu_do_interrupt(CPUState *cs)
>          case RISCV_EXCP_INST_GUEST_PAGE_FAULT:
>          case RISCV_EXCP_LOAD_GUEST_ACCESS_FAULT:
>          case RISCV_EXCP_STORE_GUEST_AMO_ACCESS_FAULT:
> -            force_hs_execp = true;
> -            /* fallthrough */
>          case RISCV_EXCP_INST_ADDR_MIS:
>          case RISCV_EXCP_INST_ACCESS_FAULT:
>          case RISCV_EXCP_LOAD_ADDR_MIS:
> @@ -973,8 +952,7 @@ void riscv_cpu_do_interrupt(CPUState *cs)
>                  env->hstatus = set_field(env->hstatus, HSTATUS_GVA, 0);
>              }
>
> -            if (riscv_cpu_virt_enabled(env) && ((hdeleg >> cause) & 1) &&
> -                !force_hs_execp) {
> +            if (riscv_cpu_virt_enabled(env) && ((hdeleg >> cause) & 1)) {
>                  /* Trap to VS mode */
>                  /*
>                   * See if we need to adjust cause. Yes if its VS mode 
> interrupt
> @@ -996,7 +974,6 @@ void riscv_cpu_do_interrupt(CPUState *cs)
>                  htval = env->guest_phys_fault_addr;
>
>                  riscv_cpu_set_virt_enabled(env, 0);
> -                riscv_cpu_set_force_hs_excep(env, 0);
>              } else {
>                  /* Trap into HS mode */
>                  env->hstatus = set_field(env->hstatus, HSTATUS_SPV, false);
> @@ -1032,7 +1009,6 @@ void riscv_cpu_do_interrupt(CPUState *cs)
>
>              /* Trapping to M mode, virt is disabled */
>              riscv_cpu_set_virt_enabled(env, 0);
> -            riscv_cpu_set_force_hs_excep(env, 0);
>          }
>
>          s = env->mstatus;
> --
> 2.30.2
>
>