Is vcpu hotplug supported in arm virt-machine now? 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 ask this question because we propose similar patch about LoongArch system in qemu mailing list, and kernel need not be modified for vcpu hotplug. 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
