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[189.204.200.163]) by smtp.gmail.com with ESMTPSA id g64sm624284qkf.41.2021.05.12.11.20.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 12 May 2021 11:20:17 -0700 (PDT) Subject: Re: [PATCH 07/11] target/ppc: added KVM fallback to fpscr manipulation To: "Bruno Larsen (billionai)" , 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: Wed, 12 May 2021 13:20:14 -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: <20210512140813.112884-8-bruno.larsen@eldorado.org.br> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::72c; envelope-from=richard.henderson@linaro.org; helo=mail-qk1-x72c.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: 2.1.23 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 5/12/21 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); } 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~