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[174.21.142.130]) by smtp.gmail.com with ESMTPSA id g70-20020a636b49000000b003823dd39d41sm11569167pgc.64.2022.03.22.17.58.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Mar 2022 17:58:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=g4ZAYkN4+Df9Z1kwRtWsg4ayeKzhHtF/+N49oTFuqzw=; b=vEsMXAdH7OX0Abv/pUT1w5q2HbmO2o905fuuVq4ndMj05R+xwYrXUSPPXQizWvSP5R 3DHyPO+NZsC2688/DqkKd4DAIqTiv5kHmHmSIkd2iMTNqnxRPRYLxVviL9wOJ4Chg/VZ Omsrvofl1IIaACbsgsMcNRdQYHwgmuwk+FzXxxZqL01cYNKgqR9UzN/mjXKuQYKi0zWV adiFOOTEl+tX8SnLPCU22fjVFeDQ1l+Cqwwieo4vTR4oUp73nfvyhWhf4YZoaZNkonp4 E1XiNW9rHpeFwylU2c6G4llD5U8GVemt/mPM74cNY4xBCBVa3sYCX8PJ7dTEwA6hTPcg TjIQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=g4ZAYkN4+Df9Z1kwRtWsg4ayeKzhHtF/+N49oTFuqzw=; b=6ZRbA2I1t5C6Zveekxa9kCemaM+T/AF9NO8ziTh+l5MDwNwDS/QfBl4RHBt4+ryfcg 3Gta/ZapF8j/royWYi2+qyMmaz01uWijI69Fk6qDBT0WQEOwRjsYjFZkhY4Dl2TrXLJ0 kQT1junBA5vpvjhu+IFIeoVLguaH35lWjMTWIPGsKd9humDnPHUI1UsUDYhp8oIBNt/R +6HVAfhHkF7EqC/hH+++5R1eg7z7AoJBcpndn8n7b79Ww6rQjmu766zUUijo12I0HDYc WflpQVW9C5R4xCpOD04oATdM3JqIyHkto9aRToMxzFizP73bnlT4X2J0iOpmxkwBq6T8 vWFw== X-Gm-Message-State: AOAM530TvKQbZy0iiPdrKD4VMdE9i9xFiVU9g/fEsOrDMMHBkBwqfl2G feZkGLOxlPusnENeIPAh+CI6i1usKlRzsg== X-Google-Smtp-Source: ABdhPJydSBRYWpWr3V6SHArNhUScPj/cfs6xXPk6To7xToLwoSgpE9vUX7A+QCN/vQpTCJFt8/5yfg== X-Received: by 2002:a17:903:3051:b0:154:6fa8:2fa3 with SMTP id u17-20020a170903305100b001546fa82fa3mr9850229pla.129.1647997124477; Tue, 22 Mar 2022 17:58:44 -0700 (PDT) From: Richard Henderson To: qemu-devel@nongnu.org Subject: [PATCH v2 2/3] linux-user/arm: Implement __kernel_cmpxchg with host atomics Date: Tue, 22 Mar 2022 17:58:38 -0700 Message-Id: <20220323005839.94327-3-richard.henderson@linaro.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220323005839.94327-1-richard.henderson@linaro.org> References: <20220323005839.94327-1-richard.henderson@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Host-Lookup-Failed: Reverse DNS lookup failed for 2607:f8b0:4864:20::102c (failed) Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=2607:f8b0:4864:20::102c; envelope-from=richard.henderson@linaro.org; helo=mail-pj1-x102c.google.com X-Spam_score_int: -6 X-Spam_score: -0.7 X-Spam_bar: / X-Spam_report: (-0.7 / 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, PDS_HP_HELO_NORDNS=0.659, RCVD_IN_DNSWL_NONE=-0.0001, RDNS_NONE=0.793, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=no 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: , Cc: Peter Maydell , laurent@vivier.eu Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) X-ZM-MESSAGEID: 1647997265931100004 Content-Type: text/plain; charset="utf-8" The existing implementation using start/end_exclusive does not provide atomicity across processes. Reviewed-by: Peter Maydell Signed-off-by: Richard Henderson --- linux-user/arm/cpu_loop.c | 87 ++++++++++++++++++++++++++++----------- 1 file changed, 62 insertions(+), 25 deletions(-) diff --git a/linux-user/arm/cpu_loop.c b/linux-user/arm/cpu_loop.c index a0e43b261c..aa2d777bf4 100644 --- a/linux-user/arm/cpu_loop.c +++ b/linux-user/arm/cpu_loop.c @@ -75,7 +75,67 @@ put_user_u16(__x, (gaddr)); \ }) =20 -/* Commpage handling -- there is no commpage for AArch64 */ +/* + * Similar to code in accel/tcg/user-exec.c, but outside the execution loo= p. + * Must be called with mmap_lock. + * We get the PC of the entry address - which is as good as anything, + * on a real kernel what you get depends on which mode it uses. + */ +static void *atomic_mmu_lookup(CPUArchState *env, uint32_t addr, int size) +{ + int need_flags =3D PAGE_READ | PAGE_WRITE_ORG | PAGE_VALID; + int page_flags; + + /* Enforce guest required alignment. */ + if (unlikely(addr & (size - 1))) { + force_sig_fault(TARGET_SIGBUS, TARGET_BUS_ADRALN, addr); + return NULL; + } + + page_flags =3D page_get_flags(addr); + if (unlikely((page_flags & need_flags) !=3D need_flags)) { + force_sig_fault(TARGET_SIGSEGV, + page_flags & PAGE_VALID ? + TARGET_SEGV_ACCERR : TARGET_SEGV_MAPERR, addr); + return NULL; + } + + return g2h(env_cpu(env), addr); +} + +/* + * See the Linux kernel's Documentation/arm/kernel_user_helpers.rst + * Input: + * r0 =3D oldval + * r1 =3D newval + * r2 =3D pointer to target value + * + * Output: + * r0 =3D 0 if *ptr was changed, non-0 if no exchange happened + * C set if *ptr was changed, clear if no exchange happened + */ +static void arm_kernel_cmpxchg32_helper(CPUARMState *env) +{ + uint32_t oldval, newval, val, addr, cpsr, *host_addr; + + oldval =3D env->regs[0]; + newval =3D env->regs[1]; + addr =3D env->regs[2]; + + mmap_lock(); + host_addr =3D atomic_mmu_lookup(env, addr, 4); + if (!host_addr) { + mmap_unlock(); + return; + } + + val =3D qatomic_cmpxchg__nocheck(host_addr, oldval, newval); + mmap_unlock(); + + cpsr =3D (val =3D=3D oldval) * CPSR_C; + cpsr_write(env, cpsr, CPSR_C, CPSRWriteByInstr); + env->regs[0] =3D cpsr ? 0 : -1; +} =20 /* * See the Linux kernel's Documentation/arm/kernel_user_helpers.txt @@ -153,36 +213,13 @@ static int do_kernel_trap(CPUARMState *env) { uint32_t addr; - uint32_t cpsr; - uint32_t val; =20 switch (env->regs[15]) { case 0xffff0fa0: /* __kernel_memory_barrier */ smp_mb(); break; case 0xffff0fc0: /* __kernel_cmpxchg */ - /* XXX: This only works between threads, not between processes. - It's probably possible to implement this with native host - operations. However things like ldrex/strex are much harder so - there's not much point trying. */ - start_exclusive(); - cpsr =3D cpsr_read(env); - addr =3D env->regs[2]; - /* FIXME: This should SEGV if the access fails. */ - if (get_user_u32(val, addr)) - val =3D ~env->regs[0]; - if (val =3D=3D env->regs[0]) { - val =3D env->regs[1]; - /* FIXME: Check for segfaults. */ - put_user_u32(val, addr); - env->regs[0] =3D 0; - cpsr |=3D CPSR_C; - } else { - env->regs[0] =3D -1; - cpsr &=3D ~CPSR_C; - } - cpsr_write(env, cpsr, CPSR_C, CPSRWriteByInstr); - end_exclusive(); + arm_kernel_cmpxchg32_helper(env); break; case 0xffff0fe0: /* __kernel_get_tls */ env->regs[0] =3D cpu_get_tls(env); --=20 2.25.1