From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D0DC33A4F4B; Thu, 14 May 2026 09:41:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778751661; cv=none; b=hrH0+TGfDrBzATV1EzmFF0Z61VE/4Hrdy2b3C1LKMCHD08NPiRTwfjo5YmCxyXmLGXKYH+zwVbUhnF9s2At5og51v5MM55lwBczaSwr5iE/12m1neUA700bzclkJH4O8rtLpxU/k4cM0z0ctdJZu/FRrArORsdldEpO7uqbHNog= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778751661; c=relaxed/simple; bh=XWBLYDMoG9UY2br2So2uu6HROTGF8oGeeKo1YXLahw8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=cv8rUmp88tvh31RoSeyX0sSrOa/oaIqttXXVvtJml2t06yPIrWrl4M6NMZFAo6In/vWb9s6dm2U36Z6rbPz1H+Q8zxvxzy5FvKlKUBMKMsZgd/i3Ox4UV72JLKJdD9/mp5LahaSBucM8T1GqXjWRWr4qpeWY2QBwq+sG7M2XRv4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=sAIwccg3; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="sAIwccg3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 75B0BC2BCB3; Thu, 14 May 2026 09:40:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778751661; bh=XWBLYDMoG9UY2br2So2uu6HROTGF8oGeeKo1YXLahw8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=sAIwccg36liT9ntaU5uLa+ZHufIghTxRLKc+jMHEf6c89yU2kIY25tC0TFITJdLiV wx3JDXHW3tOnUPHpWuyLpqfrQ6rJW3EBSiS6U0/zAVupKn6ALmfGj/r46Xfwvnz5Cm hH59FRrM95JoEnB4OYun5VeHZpRFbMs3UVFGCuvL4GtIZjk2WPOrzj9kWKrwuYF3Zi vUx0X/BVrHDQVTyVsSBm9SGBA12o5gOThs2C3IA2+i7gu2eDS3Rpnh+Ia+GDT9quva AtOXB63myHZQY1IisxG6wZYa83OCyaMCSVdxnrII56SdxLGN4FY8Wnd880lFsTMA1x ec3cQgvizuhHQ== From: "Aneesh Kumar K.V (Arm)" To: linux-coco@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: "Aneesh Kumar K.V (Arm)" , Catalin Marinas , Greg KH , Jeremy Linton , Jonathan Cameron , Lorenzo Pieralisi , Mark Rutland , Sudeep Holla , Will Deacon , Steven Price , Suzuki K Poulose Subject: [PATCH v5 3/3] coco: guest: arm64: Replace dummy CCA device with sysfs ABI Date: Thu, 14 May 2026 15:10:30 +0530 Message-ID: <20260514094030.42495-4-aneesh.kumar@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260514094030.42495-1-aneesh.kumar@kernel.org> References: <20260514094030.42495-1-aneesh.kumar@kernel.org> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The SMCCC firmware driver now creates the arm-smccc platform device and instantiates the CCA auxiliary devices once the RSI ABI is discovered. The arm64-specific arm-cca-dev platform device stub is therefore no longer needed. However, userspace has used the arm-cca-dev platform device to detect Arm CCA Realm guests [1]. Removing it without a replacement would break that detection and would also leave userspace depending on kernel device-model details. Add /sys/firmware/cca/realm_guest as a stable, architecture-provided ABI for detecting whether the kernel is running as an Arm CCA Realm guest. The file returns 1 in Realm world and 0 otherwise, similar to the existing s390 /sys/firmware/uv/prot_virt_guest interface for protected virtualization guests. Remove the dummy arm-cca-dev registration now that userspace has a dedicated CCA Realm guest indicator, and document the new ABI in Documentation/ABI/testing/sysfs-firmware-cca. [1] https://lore.kernel.org/all/4a7d84b2-2ec4-4773-a2d5-7b63d5c683cf@arm.com Signed-off-by: Aneesh Kumar K.V (Arm) --- Documentation/ABI/testing/sysfs-firmware-cca | 10 +++++ arch/arm64/kernel/rsi.c | 39 +++++++++++++++----- 2 files changed, 39 insertions(+), 10 deletions(-) create mode 100644 Documentation/ABI/testing/sysfs-firmware-cca diff --git a/Documentation/ABI/testing/sysfs-firmware-cca b/Documentation/ABI/testing/sysfs-firmware-cca new file mode 100644 index 000000000000..bf177d636b92 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-firmware-cca @@ -0,0 +1,10 @@ +What: /sys/firmware/cca/realm_guest +Date: May 2026 +Contact: Linux ARM Kernel Mailing list +Description: Read-only. Indicates whether the kernel is running as an + Arm Confidential Compute Architecture (CCA) Realm guest. + + The value is one of: + + 0: the kernel is not running as a Realm guest + 1: the kernel is running as a Realm guest diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c index 8380e5ba88d2..a3e9b3bb5679 100644 --- a/arch/arm64/kernel/rsi.c +++ b/arch/arm64/kernel/rsi.c @@ -9,6 +9,8 @@ #include #include #include +#include +#include #include #include @@ -16,6 +18,7 @@ #include static struct realm_config config; +static struct kobject *cca_kobj; unsigned long prot_ns_shared; EXPORT_SYMBOL(prot_ns_shared); @@ -160,17 +163,33 @@ void __init arm64_rsi_init(void) static_branch_enable(&rsi_present); } -static struct platform_device rsi_dev = { - .name = "arm-cca-dev", - .id = PLATFORM_DEVID_NONE +static ssize_t cca_is_realm_guest(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sysfs_emit(buf, "%d\n", is_realm_world()); +} + +static struct kobj_attribute cca_realm_guest = + __ATTR(realm_guest, 0444, cca_is_realm_guest, NULL); + +static const struct attribute *cca_realm_attrs[] = { + &cca_realm_guest.attr, + NULL, }; -static int __init arm64_create_dummy_rsi_dev(void) +static int __init realm_sysfs_init(void) { - if (is_realm_world() && - platform_device_register(&rsi_dev)) - pr_err("failed to register rsi platform device\n"); - return 0; -} + int ret; + + cca_kobj = kobject_create_and_add("cca", firmware_kobj); + if (!cca_kobj) + return -ENOMEM; -arch_initcall(arm64_create_dummy_rsi_dev) + ret = sysfs_create_files(cca_kobj, cca_realm_attrs); + if (!ret) + return 0; + + kobject_put(cca_kobj); + return ret; +} +device_initcall(realm_sysfs_init); -- 2.43.0