Re: [PATCH v4 1/2] target/riscv: separate priv from mmu_idx

["Wu, Fei" <fei2.wu@intel.com>]

On 3/23/2023 11:53 PM, Richard Henderson wrote:
> On 3/22/23 19:44, Fei Wu wrote:
>> Currently it's assumed the 2 low bits of mmu_idx map to privilege mode,
>> this assumption won't last as we are about to add more mmu_idx.
>>
>> Signed-off-by: Fei Wu <fei2.wu@intel.com>
>> ---
>>   target/riscv/cpu.h                             | 1 -
>>   target/riscv/cpu_helper.c                      | 2 +-
>>   target/riscv/insn_trans/trans_privileged.c.inc | 2 +-
>>   target/riscv/insn_trans/trans_xthead.c.inc     | 7 +------
>>   target/riscv/translate.c                       | 3 +++
>>   5 files changed, 6 insertions(+), 9 deletions(-)
>>
>> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
>> index 638e47c75a..66f7e3d1ba 100644
>> --- a/target/riscv/cpu.h
>> +++ b/target/riscv/cpu.h
>> @@ -623,7 +623,6 @@ G_NORETURN void
>> riscv_raise_exception(CPURISCVState *env,
>>   target_ulong riscv_cpu_get_fflags(CPURISCVState *env);
>>   void riscv_cpu_set_fflags(CPURISCVState *env, target_ulong);
>>   -#define TB_FLAGS_PRIV_MMU_MASK                3
>>   #define TB_FLAGS_PRIV_HYP_ACCESS_MASK   (1 << 2)
>>   #define TB_FLAGS_MSTATUS_FS MSTATUS_FS
>>   #define TB_FLAGS_MSTATUS_VS MSTATUS_VS
>> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
>> index f88c503cf4..76e1b0100e 100644
>> --- a/target/riscv/cpu_helper.c
>> +++ b/target/riscv/cpu_helper.c
>> @@ -762,7 +762,7 @@ static int get_physical_address(CPURISCVState
>> *env, hwaddr *physical,
>>        * (riscv_cpu_do_interrupt) is correct */
>>       MemTxResult res;
>>       MemTxAttrs attrs = MEMTXATTRS_UNSPECIFIED;
>> -    int mode = mmu_idx & TB_FLAGS_PRIV_MMU_MASK;
>> +    int mode = env->priv;
> 
> This is incorrect.  You must map back from mmu_idx to priv.
> Recall the semantics of MPRV.
> 
The following code (~20 lines below) takes MPRV into consideration:

    if (riscv_cpu_two_stage_lookup(mmu_idx)) {
        mode = get_field(env->hstatus, HSTATUS_SPVP);
    } else if (mode == PRV_M && access_type != MMU_INST_FETCH) {
        if (get_field(env->mstatus, MSTATUS_MPRV)) {
            mode = get_field(env->mstatus, MSTATUS_MPP);
        }
    }

I think it's the same logic as the original one.

>> diff --git a/target/riscv/insn_trans/trans_xthead.c.inc
>> b/target/riscv/insn_trans/trans_xthead.c.inc
>> index df504c3f2c..adfb53cb4c 100644
>> --- a/target/riscv/insn_trans/trans_xthead.c.inc
>> +++ b/target/riscv/insn_trans/trans_xthead.c.inc
>> @@ -265,12 +265,7 @@ static bool trans_th_tst(DisasContext *ctx,
>> arg_th_tst *a)
>>     static inline int priv_level(DisasContext *ctx)
>>   {
>> -#ifdef CONFIG_USER_ONLY
>> -    return PRV_U;
>> -#else
>> -     /* Priv level is part of mem_idx. */
>> -    return ctx->mem_idx & TB_FLAGS_PRIV_MMU_MASK;
>> -#endif
>> +    return ctx->priv;
>>   }
> 
> I guess we aren't expecting optimization to remove dead system code?
> That would be the only reason to keep the ifdef.
> 
> This function should be hoisted to translate.c, or simply replaced by
> the field access.
> 
I only want to replace mem_idx to priv here, Zhiwei might decide how to
adjust the code further.

Thanks,
Fei.

>> @@ -1162,8 +1163,10 @@ static void
>> riscv_tr_init_disas_context(DisasContextBase *dcbase, CPUState *cs)
>>       } else {
>>           ctx->virt_enabled = false;
>>       }
>> +    ctx->priv = env->priv;
> 
> Incorrect, as Zhiwei pointed out.
> I gave you the changes required to TB_FLAGS...
> 
> 
> r~