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[189.204.200.163]) by smtp.gmail.com with ESMTPSA id f132sm3656632qke.104.2021.05.13.15.45.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 May 2021 15:45:46 -0700 (PDT) Subject: Re: [PATCH 07/11] target/ppc: added KVM fallback to fpscr manipulation To: Bruno Piazera Larsen , qemu-devel@nongnu.org References: <20210512140813.112884-1-bruno.larsen@eldorado.org.br> <20210512140813.112884-8-bruno.larsen@eldorado.org.br> From: Richard Henderson Message-ID: Date: Thu, 13 May 2021 17:45:43 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::72a; envelope-from=richard.henderson@linaro.org; helo=mail-qk1-x72a.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=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: farosas@linux.ibm.com, luis.pires@eldorado.org.br, lucas.araujo@eldorado.org.br, fernando.valle@eldorado.org.br, qemu-ppc@nongnu.org, matheus.ferst@eldorado.org.br, david@gibson.dropbear.id.au Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 5/13/21 11:36 AM, Bruno Piazera Larsen wrote: > > On 12/05/2021 15:20, Richard Henderson wrote: >> On 5/12/21 9:08 AM, Bruno Larsen (billionai) wrote: >>> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c >>> index 104a308abb..a8a720eb48 100644 >>> --- a/target/ppc/kvm.c >>> +++ b/target/ppc/kvm.c >>> @@ -2947,3 +2947,17 @@ bool kvm_arch_cpu_check_are_resettable(void) >>>   { >>>       return true; >>>   } >>> + >>> +void kvmppc_store_fpscr(CPUPPCState *env, uint64_t arg, uint32_t mask) >>> +{ >>> +    CPUState *cs = env_cpu(env); >>> +    struct kvm_one_reg reg; >>> +    int ret; >>> +    reg.id = KVM_REG_PPC_FPSCR; >>> +    reg.addr = (uintptr_t) &env->fpscr; >>> +    ret = kvm_vcpu_ioctl(cs, KVM_SET_ONE_REG, ®); >>> +    if (ret < 0) >>> +    { >>> +        fprintf(stderr, "Unable to set FPSCR to KVM: %s", strerror(errno)); >>> +    } >>> +} >> >> This is all unnecessary.  All you need to do is store to env->fpscr and the >> value will be synced back with kvm_put_fp. >> >> I'll note that some of the trouble you may be having with extracting >> helper_store_fpscr to a ppc_store_fpscr function is due to an existing bug in >> the tcg code: >> >> Storing to fpscr should *never* raise an exception -- see MTFSF, MTFSB0, >> MTFSB1.  Thus the mucking about with cs->exception_index and env->error_code >> is incorrect. >> >> In addition, the masking is being done weirdly and could use a complete >> overhaul. >> >> This could all be rewritten as >> >> -- %< -- cpu.h >> >>  /* Invalid operation exception summary */ >> - #define fpscr_ix ((env->fpscr) & ((1 << FPSCR_VXSNAN) ... >> + #define FPSCR_IX  ((1 << FPSCR_VXSNAN) | ...) >> >> -- %< -- cpu.c >> >> // move fpscr_set_rounding_mode here >> >> void ppc_store_fpscr(CPUPPCState *env, target_ulong val) >> { >>     /* Recompute exception summary state. */ >>     val &= ~(FP_VX | FP_FEX); >>     if (val & FPSCR_IX) { >>         val |= FP_VX; >>     } >>     if ((val >> FPSCR_XX) & (val >> FPSCR_XE) & 0x1f) { >>         val |= FP_FEX; >>     } >>     env->fpscr = val; >>     if (tcg_enabled()) { >>         fpscr_set_rounding_mode(env); >>     } >> } >> >> -- %< -- fpu_helper.c >> >> void helper_store_fpscr(CPUPPCState *env, target_ulong val, >>                         uint32_t nibbles) >> { >>     target_ulong mask = 0; >> >>     /* TODO: Push this expansion back to translation time. */ >>     for (int i = 0; i < sizeof(target_ulong) * 2; ++i) { >>         if (nibbles & (1 << i)) { >>             mask |= (target_ulong)0xf << (4 * i); >>         } >>     } >> >>     val = (val & mask) | (env->fpscr & ~mask); >>     ppc_store_fpscr(env, val); >> } > That expansion can't be moved to translation time, because gdbstub would also > need that code in a variety of functions, so better to keep it in that central > location, >> >> void helper_fpscr_clrbit(CPUPPCState *env, uint32_t bit) >> { >>     uint32_t mask = 1u << bit; >>     if (env->fpscr & mask) { >>         ppc_store_fpscr(env, env->fpscr & ~mask); >>     } >> } >> >> void helper_fpscr_setbit(CPUPPCState *env, uint32_t bit) >> { >>     uint32_t mask = 1u << bit; >>     if (!(env->fpscr & mask)) { >>         ppc_store_fpscr(env, env->fpscr | mask); >>     } >> } >> >> There are a couple of other uses of fpscr_set_rounding_mode, where the >> softfloat value is changed temporarily (do_fri, VSX_ROUND). These should >> simply save the previous softfloat value (using get_float_rounding_mode) >> around the operation instead of re-computing from fpscr. >> >> Which leaves us with exactly one use of fpscr_set_rounding_mode, which can >> then be moved to cpu.c next to ppc_store_fpscr. >> >> >> r~ > > I was implementing this solution, but ran into a problem: We needed store_fpscr > for gdbstub.c, that's the original reason we made that new function to begin > with. This solution, although it improves the handling of fpscr, doesn't fix > the original problem. Why not? Did you miss the cpu.c cut at the very top? > What I think we can do is put the logic that is in helper_store_fpscr into > store_fpscr, move it to cpu.c, and have the helper call the non-helper > function. That way we conserve helper_* as TCG-specific and have the overhaul. That is exactly what I have written above. r~