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

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

On 3/23/2023 2:59 PM, LIU Zhiwei wrote:
> 
> On 2023/3/23 14:00, Wu, Fei wrote:
>> On 3/23/2023 1:37 PM, LIU Zhiwei wrote:
>>> On 2023/3/23 10:44, 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.
>>> For patch set has more than 1 patch, usually add a cover letter.
>> This is cover letter:
>>     https://www.mail-archive.com/qemu-devel@nongnu.org/msg950849.html
>>
>> I added scripts/get_maintainer.pl to .git/config,
> Interesting.
>> it couldn't find out
>> the maintainers for the cover letter, so I added the mail lists to "To"
>> manually.
> Maybe you should also cc to maintainers manually. I don't know the
> automatically way.
>>
>>>> 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;
>>>>        bool use_background = false;
>>>>        hwaddr ppn;
>>>>        RISCVCPU *cpu = env_archcpu(env);
>>>> diff --git a/target/riscv/insn_trans/trans_privileged.c.inc
>>>> b/target/riscv/insn_trans/trans_privileged.c.inc
>>>> index 59501b2780..9305b18299 100644
>>>> --- a/target/riscv/insn_trans/trans_privileged.c.inc
>>>> +++ b/target/riscv/insn_trans/trans_privileged.c.inc
>>>> @@ -52,7 +52,7 @@ static bool trans_ebreak(DisasContext *ctx,
>>>> arg_ebreak *a)
>>>>         * that no exception will be raised when fetching them.
>>>>         */
>>>>    -    if (semihosting_enabled(ctx->mem_idx < PRV_S) &&
>>>> +    if (semihosting_enabled(ctx->priv < PRV_S) &&
>>>>            (pre_addr & TARGET_PAGE_MASK) == (post_addr &
>>>> TARGET_PAGE_MASK)) {
>>>>            pre    = opcode_at(&ctx->base, pre_addr);
>>>>            ebreak = opcode_at(&ctx->base, ebreak_addr);
>>>> 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;
>>>>    }
>>>>      /* Test if priv level is M, S, or U (cannot fail). */
>>>> diff --git a/target/riscv/translate.c b/target/riscv/translate.c
>>>> index 0ee8ee147d..e8880f9423 100644
>>>> --- a/target/riscv/translate.c
>>>> +++ b/target/riscv/translate.c
>>>> @@ -69,6 +69,7 @@ typedef struct DisasContext {
>>>>        uint32_t mstatus_hs_fs;
>>>>        uint32_t mstatus_hs_vs;
>>>>        uint32_t mem_idx;
>>>> +    uint32_t priv;
>>>>        /* Remember the rounding mode encoded in the previous fp
>>>> instruction,
>>>>           which we have already installed into env->fp_status.  Or
>>>> -1 for
>>>>           no previous fp instruction.  Note that we exit the TB when
>>>> writing
>>>> @@ -1162,8 +1163,10 @@ static void
>>>> riscv_tr_init_disas_context(DisasContextBase *dcbase, CPUState *cs)
>>>>        } else {
>>>>            ctx->virt_enabled = false;
>>>>        }
>>>> +    ctx->priv = env->priv;
>>> This is not right. You should put env->priv into tb flags before you use
>>> it in translation.
>>>
>> I see some other env usages in this function,
> Don't do it that way. It just be merged by accident. It will make review
> harder and probably be wrong.
>> when will env->priv and
>> tb_flags.priv mismatch (assume we have recorded priv in tb_flags)?
> 
> We always record the env->priv in tb flags if we don't merge your second
> patch in this patch set.
> After your second patch, we will not record the env->priv  into tb flags
> when SUM is 1. Thus we may execute a S-mode code when we actually in
> M-mode, which is forbidden by RISC-V.
> 
Do you mean the case of calling tb_lookup(flags) to reuse TB? priv
should be part of flags or it finds the wrong TB, SUM not?

Thanks,
Fei.

> Zhiwei
> 
>>
>> Thanks,
>> Fei.
>>
>>> Zhiwei
>>>
>>>>    #else
>>>>        ctx->virt_enabled = false;
>>>> +    ctx->priv = PRV_U;
>>>>    #endif
>>>>        ctx->misa_ext = env->misa_ext;
>>>>        ctx->frm = -1;  /* unknown rounding mode */