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GET /api/patches/2224042/?format=api
{ "id": 2224042, "url": "http://patchwork.ozlabs.org/api/patches/2224042/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/patch/20260416165353.589569-3-peter.maydell@linaro.org/", "project": { "id": 14, "url": "http://patchwork.ozlabs.org/api/projects/14/?format=api", "name": "QEMU Development", "link_name": "qemu-devel", "list_id": "qemu-devel.nongnu.org", "list_email": "qemu-devel@nongnu.org", "web_url": "", "scm_url": "", "webscm_url": "", "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<20260416165353.589569-3-peter.maydell@linaro.org>", "list_archive_url": null, "date": "2026-04-16T16:53:52", "name": "[v2,2/3] target/arm: Allow 'aarch64=off' to be set for TCG CPUs", "commit_ref": null, "pull_url": null, "state": "accepted", "archived": false, "hash": "a8ecbc59ec555ef67bd9fc425c8161ec4a7bbff6", "submitter": { "id": 5111, "url": "http://patchwork.ozlabs.org/api/people/5111/?format=api", "name": "Peter Maydell", "email": "peter.maydell@linaro.org" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/qemu-devel/patch/20260416165353.589569-3-peter.maydell@linaro.org/mbox/", "series": [ { "id": 500186, "url": "http://patchwork.ozlabs.org/api/series/500186/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/list/?series=500186", "date": "2026-04-16T16:53:52", "name": null, "version": 2, "mbox": "http://patchwork.ozlabs.org/series/500186/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2224042/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2224042/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org>", "X-Original-To": "incoming@patchwork.ozlabs.org", "Delivered-To": "patchwork-incoming@legolas.ozlabs.org", "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=linaro.org header.i=@linaro.org header.a=rsa-sha256\n header.s=google header.b=Oirh1zMy;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; helo=lists1p.gnu.org;\n envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)" ], "Received": [ "from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17])\n\t(using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4fxPJP4M3Dz1yHP\n\tfor <incoming@patchwork.ozlabs.org>; Fri, 17 Apr 2026 02:55:00 +1000 (AEST)", "from localhost ([::1] helo=lists1p.gnu.org)\n\tby lists1p.gnu.org with esmtp (Exim 4.90_1)\n\t(envelope-from <qemu-devel-bounces@nongnu.org>)\n\tid 1wDPyi-0006Ay-Kh; Thu, 16 Apr 2026 12:54:08 -0400", "from eggs.gnu.org ([2001:470:142:3::10])\n by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)\n (Exim 4.90_1) (envelope-from <peter.maydell@linaro.org>)\n id 1wDPyh-0006A7-30\n for qemu-devel@nongnu.org; Thu, 16 Apr 2026 12:54:07 -0400", "from mail-wm1-x32a.google.com ([2a00:1450:4864:20::32a])\n by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128)\n (Exim 4.90_1) (envelope-from <peter.maydell@linaro.org>)\n id 1wDPyf-0007ou-7Z\n for qemu-devel@nongnu.org; Thu, 16 Apr 2026 12:54:06 -0400", "by mail-wm1-x32a.google.com with SMTP id\n 5b1f17b1804b1-488ba840146so81567965e9.1\n for <qemu-devel@nongnu.org>; Thu, 16 Apr 2026 09:54:04 -0700 (PDT)", "from lanath.. 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charset=UTF-8", "Content-Transfer-Encoding": "8bit", "Received-SPF": "pass client-ip=2a00:1450:4864:20::32a;\n envelope-from=peter.maydell@linaro.org; helo=mail-wm1-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,\n DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001,\n 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": "qemu development <qemu-devel.nongnu.org>", "List-Unsubscribe": "<https://lists.nongnu.org/mailman/options/qemu-devel>,\n <mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>", "List-Archive": "<https://lists.nongnu.org/archive/html/qemu-devel>", "List-Post": "<mailto:qemu-devel@nongnu.org>", "List-Help": "<mailto:qemu-devel-request@nongnu.org?subject=help>", "List-Subscribe": "<https://lists.nongnu.org/mailman/listinfo/qemu-devel>,\n <mailto:qemu-devel-request@nongnu.org?subject=subscribe>", "Errors-To": "qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org", "Sender": "qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org" }, "content": "Allow the 'aarch64=off' property, which is currently KVM-only, to\nbe set for TCG CPUs also.\n\nNote that we don't permit it on the qemu-aarch64 user-mode binary:\nthis makes no sense as that executable can only handle AArch64\nsyscalls (and it would also assert at startup since it doesn't\ncompile in the A32-specific GDB xml files like arm-neon.xml).\n\nSigned-off-by: Peter Maydell <peter.maydell@linaro.org>\nReviewed-by: Richard Henderson <richard.henderson@linaro.org>\nTested-by: Clément Chigot <chigot@adacore.com>\n---\nv1->v2: slight tweak to the docs wording\n---\n docs/system/arm/cpu-features.rst | 10 +++++----\n target/arm/cpu-features.h | 5 +++++\n target/arm/cpu.c | 36 ++++++++++++++++++++++++++++----\n tests/qtest/arm-cpu-features.c | 8 ++-----\n 4 files changed, 45 insertions(+), 14 deletions(-)", "diff": "diff --git a/docs/system/arm/cpu-features.rst b/docs/system/arm/cpu-features.rst\nindex ce19ae6a04..10b0eff27e 100644\n--- a/docs/system/arm/cpu-features.rst\n+++ b/docs/system/arm/cpu-features.rst\n@@ -23,10 +23,12 @@ not implement ARMv8-A, will not have the ``aarch64`` CPU property.\n QEMU's support may be limited for some CPU features, only partially\n supporting the feature or only supporting the feature under certain\n configurations. For example, the ``aarch64`` CPU feature, which, when\n-disabled, enables the optional AArch32 CPU feature, is only supported\n-when using the KVM accelerator and when running on a host CPU type that\n-supports the feature. While ``aarch64`` currently only works with KVM,\n-it could work with TCG. CPU features that are specific to KVM are\n+disabled, enables the optional AArch32 CPU feature, can only be set to\n+``off`` on the TCG and KVM accelerators, and it cannot be set to\n+``off`` under KVM unless running on a host CPU type that supports\n+running guests in AArch32.\n+\n+CPU features that are inherently specific to KVM are\n prefixed with \"kvm-\" and are described in \"KVM VCPU Features\".\n \n CPU Feature Probing\ndiff --git a/target/arm/cpu-features.h b/target/arm/cpu-features.h\nindex b683c9551a..6e5212ff6c 100644\n--- a/target/arm/cpu-features.h\n+++ b/target/arm/cpu-features.h\n@@ -1071,6 +1071,11 @@ static inline bool isar_feature_aa64_aa32_el2(const ARMISARegisters *id)\n return FIELD_EX64_IDREG(id, ID_AA64PFR0, EL2) >= 2;\n }\n \n+static inline bool isar_feature_aa64_aa32_el3(const ARMISARegisters *id)\n+{\n+ return FIELD_EX64_IDREG(id, ID_AA64PFR0, EL3) >= 2;\n+}\n+\n static inline bool isar_feature_aa64_ras(const ARMISARegisters *id)\n {\n return FIELD_EX64_IDREG(id, ID_AA64PFR0, RAS) != 0;\ndiff --git a/target/arm/cpu.c b/target/arm/cpu.c\nindex 11d3437843..347616fa5a 100644\n--- a/target/arm/cpu.c\n+++ b/target/arm/cpu.c\n@@ -1248,10 +1248,38 @@ static void aarch64_cpu_set_aarch64(Object *obj, bool value, Error **errp)\n * uniform execution state like do_interrupt.\n */\n if (value == false) {\n- if (!kvm_enabled() || !kvm_arm_aarch32_supported()) {\n- error_setg(errp, \"'aarch64' feature cannot be disabled \"\n- \"unless KVM is enabled and 32-bit EL1 \"\n- \"is supported\");\n+ if (kvm_enabled()) {\n+ if (!kvm_arm_aarch32_supported()) {\n+ error_setg(errp, \"'aarch64' feature cannot be disabled for KVM \"\n+ \"because this host does not support 32-bit EL1\");\n+ return;\n+ }\n+ } else if (tcg_enabled()) {\n+#ifdef CONFIG_USER_ONLY\n+ error_setg(errp, \"'aarch64' feature cannot be disabled for \"\n+ \"usermode emulator qemu-aarch64; use qemu-arm instead\");\n+ return;\n+#else\n+ bool aa32_at_highest_el;\n+ if (arm_feature(&cpu->env, ARM_FEATURE_EL3)) {\n+ aa32_at_highest_el = cpu_isar_feature(aa64_aa32_el3, cpu);\n+ } else if (arm_feature(&cpu->env, ARM_FEATURE_EL2)) {\n+ aa32_at_highest_el = cpu_isar_feature(aa64_aa32_el2, cpu);\n+ } else {\n+ aa32_at_highest_el = cpu_isar_feature(aa64_aa32_el1, cpu);\n+ }\n+\n+ if (!aa32_at_highest_el) {\n+ error_setg(errp, \"'aarch64' feature cannot be disabled for \"\n+ \"this TCG CPU because it does not support 32-bit \"\n+ \"execution at its highest implemented exception \"\n+ \"level\");\n+ return;\n+ }\n+#endif\n+ } else {\n+ error_setg(errp, \"'aarch64' feature cannot be disabled for \"\n+ \"this accelerator\");\n return;\n }\n unset_feature(&cpu->env, ARM_FEATURE_AARCH64);\ndiff --git a/tests/qtest/arm-cpu-features.c b/tests/qtest/arm-cpu-features.c\nindex bbdd89a81d..cb4d01fd46 100644\n--- a/tests/qtest/arm-cpu-features.c\n+++ b/tests/qtest/arm-cpu-features.c\n@@ -493,12 +493,8 @@ static void test_query_cpu_model_expansion(const void *data)\n sve_tests_default(qts, \"max\");\n pauth_tests_default(qts, \"max\");\n \n- /* Test that features that depend on KVM generate errors without. */\n- assert_error(qts, \"max\",\n- \"'aarch64' feature cannot be disabled \"\n- \"unless KVM is enabled and 32-bit EL1 \"\n- \"is supported\",\n- \"{ 'aarch64': false }\");\n+ /* TCG allows us to turn off AArch64 on the 'max' CPU type */\n+ assert_set_feature(qts, \"max\", \"aarch64\", false);\n }\n \n qtest_quit(qts);\n", "prefixes": [ "v2", "2/3" ] }