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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH for-8.1 17/17] target/riscv: rework write_misa() Content-Language: en-US To: LIU Zhiwei , qemu-devel@nongnu.org Cc: qemu-riscv@nongnu.org, alistair.francis@wdc.com, bmeng@tinylab.org, liweiwei@iscas.ac.cn, palmer@rivosinc.com References: <20230308201925.258223-1-dbarboza@ventanamicro.com> <20230308201925.258223-18-dbarboza@ventanamicro.com> From: Daniel Henrique Barboza In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::32a; envelope-from=dbarboza@ventanamicro.com; helo=mail-ot1-x32a.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 3/9/23 04:27, LIU Zhiwei wrote: > > On 2023/3/9 4:19, Daniel Henrique Barboza wrote: >> write_misa() must use as much common logic as possible, only specifying >> the bits that are exclusive to the CSR write operation and TCG >> internals. >> >> Rewrite write_misa() to work as follows: >> >> - supress RVC right after verifying that we're not updating RVG; >> >> - mask the write using misa_ext_mask to avoid enabling unsupported >>    extensions; >> >> - emulate the steps done by the cpu init() functions: set cpu->cfg using >>    the desired misa value, validate it, and then commit; >> >> - fallback if the validation step fails. We'll need to re-write cpu->cfg >>    with the original misa_ext value for the hart. >> >> Let's keep write_misa() as experimental for now until this logic gains >> enough mileage. >> >> Signed-off-by: Daniel Henrique Barboza >> --- >>   target/riscv/cpu.c |  7 +++--- >>   target/riscv/cpu.h |  2 ++ >>   target/riscv/csr.c | 53 +++++++++++++++++++++------------------------- >>   3 files changed, 29 insertions(+), 33 deletions(-) >> >> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c >> index 7be6a86305..4b2be32de3 100644 >> --- a/target/riscv/cpu.c >> +++ b/target/riscv/cpu.c >> @@ -281,8 +281,7 @@ static uint32_t riscv_get_misa_ext_with_cpucfg(RISCVCPUConfig *cfg) >>       return ext; >>   } >> -static void riscv_set_cpucfg_with_misa(RISCVCPUConfig *cfg, >> -                                       uint32_t misa_ext) >> +static void riscv_set_cpucfg_with_misa(RISCVCPUConfig *cfg, uint32_t misa_ext) >>   { >>       cfg->ext_i = misa_ext & RVI; >>       cfg->ext_e = misa_ext & RVE; >> @@ -299,7 +298,7 @@ static void riscv_set_cpucfg_with_misa(RISCVCPUConfig *cfg, >>       cfg->ext_g = misa_ext & RVG; >>   } >> -static void set_misa(CPURISCVState *env, RISCVMXL mxl, uint32_t ext) >> +void set_misa(CPURISCVState *env, RISCVMXL mxl, uint32_t ext) >>   { >>       env->misa_mxl_max = env->misa_mxl = mxl; >>       env->misa_ext_mask = env->misa_ext = ext; >> @@ -995,7 +994,7 @@ static void riscv_cpu_disable_priv_spec_isa_exts(RISCVCPU *cpu) >>    * Check consistency between chosen extensions while setting >>    * cpu->cfg accordingly, doing a set_misa() in the end. >>    */ >> -static void riscv_cpu_validate_set_extensions(RISCVCPU *cpu, Error **errp) >> +void riscv_cpu_validate_set_extensions(RISCVCPU *cpu, Error **errp) >>   { >>       RISCVCPUClass *mcc = RISCV_CPU_GET_CLASS(cpu); >>       CPUClass *cc = CPU_CLASS(mcc); >> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h >> index 013a1389d6..d64d0f8dd6 100644 >> --- a/target/riscv/cpu.h >> +++ b/target/riscv/cpu.h >> @@ -591,6 +591,8 @@ bool riscv_cpu_tlb_fill(CPUState *cs, vaddr address, int size, >>                           bool probe, uintptr_t retaddr); >>   char *riscv_isa_string(RISCVCPU *cpu); >>   void riscv_cpu_list(void); >> +void set_misa(CPURISCVState *env, RISCVMXL mxl, uint32_t ext); >> +void riscv_cpu_validate_set_extensions(RISCVCPU *cpu, Error **errp); >>   #define cpu_list riscv_cpu_list >>   #define cpu_mmu_index riscv_cpu_mmu_index >> diff --git a/target/riscv/csr.c b/target/riscv/csr.c >> index 02a5c2a5ca..2e75c75fcc 100644 >> --- a/target/riscv/csr.c >> +++ b/target/riscv/csr.c >> @@ -1342,6 +1342,11 @@ static RISCVException read_misa(CPURISCVState *env, int csrno, >>   static RISCVException write_misa(CPURISCVState *env, int csrno, >>                                    target_ulong val) >>   { >> +    RISCVCPU *cpu = env_archcpu(env); >> +    uint32_t hart_ext_mask = env->misa_ext_mask; >> +    uint32_t hart_ext = env->misa_ext; >> +    Error *local_err = NULL; >> + >>       if (!riscv_cpu_cfg(env)->misa_w) { >>           /* drop write to misa */ >>           return RISCV_EXCP_NONE; >> @@ -1352,34 +1357,6 @@ static RISCVException write_misa(CPURISCVState *env, int csrno, >>           return RISCV_EXCP_NONE; >>       } >> -    /* 'I' or 'E' must be present */ >> -    if (!(val & (RVI | RVE))) { >> -        /* It is not, drop write to misa */ >> -        return RISCV_EXCP_NONE; >> -    } >> - >> -    /* 'E' excludes all other extensions */ >> -    if (val & RVE) { >> -        /* >> -         * when we support 'E' we can do "val = RVE;" however >> -         * for now we just drop writes if 'E' is present. >> -         */ >> -        return RISCV_EXCP_NONE; >> -    } >> - >> -    /* >> -     * misa.MXL writes are not supported by QEMU. >> -     * Drop writes to those bits. >> -     */ >> - >> -    /* Mask extensions that are not supported by this hart */ >> -    val &= env->misa_ext_mask; >> - >> -    /* 'D' depends on 'F', so clear 'D' if 'F' is not present */ >> -    if ((val & RVD) && !(val & RVF)) { >> -        val &= ~RVD; >> -    } >> - >>       /* >>        * Suppress 'C' if next instruction is not aligned >>        * TODO: this should check next_pc >> @@ -1388,18 +1365,36 @@ static RISCVException write_misa(CPURISCVState *env, int csrno, >>           val &= ~RVC; >>       } >> +    /* Mask extensions that are not supported by this hart */ >> +    val &= hart_ext_mask; >> + >>       /* If nothing changed, do nothing. */ >>       if (val == env->misa_ext) { >>           return RISCV_EXCP_NONE; >>       } >> +    /* >> +     * Validate the new configuration. Rollback to previous >> +     * values if something goes wrong. >> +     */ >> +    set_misa(env, env->misa_mxl, val); >> +    riscv_cpu_validate_set_extensions(cpu, &local_err); > > Can we split the riscv_cpu_validate_set_extensions to validate and set functions? If so, we can remove the restore work here. Good idea. I'll do that. > And I think the fields in misa are WARL, we should be able to write into each single field if it is legal. The ISA mentions that: ========= An implementation may impose additional constraints on the collective setting of two or more misa fields, in which case they function collectively as a single WARL field. An attempt to write an unsupported combination causes those bits to be set to some supported combination. ========= And I think this is what we were already doing here: filter what we cannot support before writing the CSR. Thanks, Daniel > > Zhiwei > >> +    if (local_err) { >> +        set_misa(env, env->misa_mxl, hart_ext); >> +        return RISCV_EXCP_NONE; >> +    } >> + >> +    /* >> +     * Keep the original misa_ext_mask from the hart. >> +     */ >> +    env->misa_ext_mask = hart_ext_mask; >> + >>       if (!(val & RVF)) { >>           env->mstatus &= ~MSTATUS_FS; >>       } >>       /* flush translation cache */ >>       tb_flush(env_cpu(env)); >> -    env->misa_ext = val; >>       env->xl = riscv_cpu_mxl(env); >>       return RISCV_EXCP_NONE; >>   }