From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) (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 4AAFE15A5; Wed, 19 Jul 2023 02:35:28 +0000 (UTC) Received: from lhrpeml500006.china.huawei.com (unknown [172.18.147.207]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4R5Kc000Dtz67QB0; Wed, 19 Jul 2023 10:32:47 +0800 (CST) Received: from lhrpeml500001.china.huawei.com (7.191.163.213) by lhrpeml500006.china.huawei.com (7.191.161.198) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.27; Wed, 19 Jul 2023 03:35:20 +0100 Received: from lhrpeml500001.china.huawei.com ([7.191.163.213]) by lhrpeml500001.china.huawei.com ([7.191.163.213]) with mapi id 15.01.2507.027; Wed, 19 Jul 2023 03:35:20 +0100 From: Salil Mehta To: "steven.price@arm.com" , Suzuki K Poulose , Jean-Philippe Brucker , "james.morse@arm.com" , "linux-coco@lists.linux.dev" , "kvmarm@lists.linux.dev" CC: Catalin Marinas , Jonathan Cameron , Marc Zyngier , Will Deacon , "christoffer.dall@arm.com" , "oliver.upton@linux.dev" , "mark.rutland@arm.com" , "pbonzini@redhat.com" , "Salil Mehta" , "andrew.jones@linux.dev" , yuzenghui , "kvmarm@lists.cs.columbia.edu" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" Subject: [Question - ARM CCA] vCPU Hotplug Support in ARM Realm world might require ARM spec change? Thread-Topic: [Question - ARM CCA] vCPU Hotplug Support in ARM Realm world might require ARM spec change? Thread-Index: Adm55YYLPryt1tEKR0alBn01xBiFBw== Date: Wed, 19 Jul 2023 02:35:19 +0000 Message-ID: <9cb24131a09a48e9a622e92bf8346c9d@huawei.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.48.147.181] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-CFilter-Loop: Reflected [Reposting it here from Linaro Open Discussion List for more eyes to look a= t] Hello, I have recently started to dabble with ARM CCA stuff and check if our recent changes to support vCPU Hotplug in ARM64 can work in the realm world. I have realized that in the RMM specification[1] PSCI_CPU_ON command(B5.3.3) does not handles the PSCI_DENIED return code(B5.4.2), from the host. This might be required to support vCPU Hotplug feature in the realm world in future. vCPU Hotplug is an important feature to support kata-containers in realm world as it reduces the VM boot time and facilitates dynamic adjustment of vCPUs (which I think should be true even with Realm world as current implementation only makes use of the PSCI_ON/OFF to realize the Hotplug look-like effect?) As per our recent changes [2], [3] related to support vCPU Hotplug on ARM64, we handle the guest exits due to SMC/HVC Hypercall in the user-space i.e. VMM/Qemu. In realm world, REC Exits to host due to PSCI_CPU_ON should undergo similar policy checks and I think, 1. Host should *deny* to online the target vCPUs which are NOT plugged 2. This means target REC should be denied by host. Can host call RMI_PSCI_COMPETE in such s case?=20 3. The *return* value (B5.3.3.1.3 Output values) should be PSCI_DENIED 4. Failure condition (B5.3.3.2) should be amended with runnable pre: target_rec.flags.runnable =3D=3D NOT_RUNNABLE (?) post: result =3D=3D PSCI_DENIED (?) 5. Change would also be required in the flow (D1.4 PSCI flows) depicting=20 PSCI_CPU_ON flow (D1.4.1) =20 I do understand that ARM CCA support is in its infancy stage and discussing about vCPU Hotplug in realm world seem to be a far-fetched idea right now. But specification changes require lot of time and if this change is really required then it should be further discussed within ARM.=20 Many thanks! Bes regards Salil References: [1] https://developer.arm.com/documentation/den0137/latest/ [2] https://github.com/salil-mehta/qemu.git virt-cpuhp-armv8/rfc-v1-port110= 52023.dev-1 [3] https://git.gitlab.arm.com/linux-arm/linux-jm.git virtual_cpu_hotplug/r= fc/v2