在 2023/7/25 08:56, Salil Mehta 写道: > Hi Bibo, > >> From: bibo mao <maobibo@xxxxxxxxxxx> >> Sent: Tuesday, July 25, 2023 1:29 AM >> To: Salil Mehta <salil.mehta@xxxxxxxxxx> >> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>; Jonathan Cameron >> <jonathan.cameron@xxxxxxxxxx>; Marc Zyngier <maz@xxxxxxxxxx>; Will Deacon >> <will@xxxxxxxxxx>; christoffer.dall@xxxxxxx; oliver.upton@xxxxxxxxx; >> mark.rutland@xxxxxxx; pbonzini@xxxxxxxxxx; Salil Mehta >> <salil.mehta@xxxxxxxxxx>; andrew.jones@xxxxxxxxx; yuzenghui >> <yuzenghui@xxxxxxxxxx>; kvmarm@xxxxxxxxxxxxxxxxxxxxx; linux-arm- >> kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; >> kvm@xxxxxxxxxxxxxxx; qemu-devel@xxxxxxxxxx; james.morse@xxxxxxx; >> steven.price@xxxxxxx; Suzuki K Poulose <suzuki.poulose@xxxxxxx>; Jean- >> Philippe Brucker <jean-philippe@xxxxxxxxxx>; kvmarm@xxxxxxxxxxxxxxx; linux- >> coco@xxxxxxxxxxxxxxx >> Subject: Re: [Question - ARM CCA] vCPU Hotplug Support in ARM Realm world >> might require ARM spec change? >> >> Is vcpu hotplug supported in arm virt-machine now? > > Not yet. We are working on it. Please check the RFCs being tested. > > > [1] Pre-RFC V2 Changes: Support of Virtual CPU Hotplug for ARMv8 Arch (WIP) > https://github.com/salil-mehta/qemu.git virt-cpuhp-armv8/rfc-v1-port11052023.dev-1 > [2] [RFC PATCH 00/32] ACPI/arm64: add support for virtual cpuhotplug > https://git.gitlab.arm.com/linux-arm/linux-jm.git virtual_cpu_hotplug/rfc/v2 > > >> There is arm64 vcpu hotplug patch in qemu mailing list, however it is not merged. >> I do not know why it is not merged. > > > I think you are referring to patches [3], [4]? Please follow the discussion > for details. yeap, we reference the patch [3], [4] and benefit from them greatly -:) The patch for LoongArch vcpu hotplug link is: https://lore.kernel.org/qemu-devel/cover.1689837093.git.lixianglai@xxxxxxxxxxx/T/#t Regards Bibo Mao > > > [3] [PATCH RFC 00/22] Support of Virtual CPU Hotplug for ARMv8 Arch > https://lore.kernel.org/all/20200613213629.21984-1-salil.mehta@xxxxxxxxxx/ > [4] [PATCH RFC 0/4] Changes to Support *Virtual* CPU Hotplug for ARM64 > https://lore.kernel.org/all/20200625133757.22332-1-salil.mehta@xxxxxxxxxx/#r > > > In summary, there were some ARM64 Architecture constraints which were being > violated in the earlier patches of the kernel [4] so we had to re-think of the > kernel changes. The Qemu part mostly remains same with some new introductions > of Guest HVC/SMC hyper call exit handling in user space etc. for policy checks > in VMM/Qemu. > > > You can follow the KVMForum conference presentations [5], [6] delivered in the > year 2020 and 2023 to get hold of more details related to this. > > > [5] KVMForum 2023: Challenges Revisited in Supporting Virt CPU Hotplug on architectures that don't Support CPU Hotplug (like ARM64) > https://kvm-forum.qemu.org/2023/talk/9SMPDQ/ > [6] KVMForum 2020: Challenges in Supporting Virtual CPU Hotplug on SoC Based Systems (like ARM64) > https://kvmforum2020.sched.com/event/eE4m > > > >> I ask this question because we propose >> similar patch about LoongArch system in qemu mailing list, and kernel need not be >> modified for vcpu hotplug. > > > Could you please share the link of your patches so that we can have a look and > draw a comparison? > > > Thanks > Salil. > >> >> Regards >> Bibo, mao >> >> 在 2023/7/19 10:35, Salil Mehta 写道: >>> [Reposting it here from Linaro Open Discussion List for more eyes to look >> at] >>> >>> 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? >>> 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 == NOT_RUNNABLE (?) >>> post: result == PSCI_DENIED (?) >>> 5. Change would also be required in the flow (D1.4 PSCI flows) depicting >>> PSCI_CPU_ON flow (D1.4.1) >>> >>> >>> 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. >>> >>> 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-port11052023.dev-1 >>> [3] https://git.gitlab.arm.com/linux-arm/linux-jm.git virtual_cpu_hotplug/rfc/v2
