Messages in this thread | | | Date | Thu, 27 Jul 2023 17:40:30 +0100 | Subject | Re: [Question - ARM CCA] vCPU Hotplug Support in ARM Realm world might require ARM spec change? | From | Suzuki K Poulose <> |
| |
On 27/07/2023 15:24, Salil Mehta wrote: > Hi Suzuki, > >> From: Suzuki K Poulose <suzuki.poulose@arm.com> >> Sent: Tuesday, July 25, 2023 12:20 PM >> >> Hi Salil >> >> On 25/07/2023 01:05, Salil Mehta wrote: >>> Hi Suzuki, >>> Sorry for replying late as I was on/off last week to undergo some medical test. >>> >>>> From: Suzuki K Poulose <suzuki.poulose@arm.com> >>>> Sent: Monday, July 24, 2023 5:27 PM >>>> >>>> Hi Salil >>>> >>>> On 19/07/2023 10:28, Suzuki K Poulose wrote: >>>>> Hi Salil >>>>> >>>>> Thanks for raising this. >>>>> >>>>> On 19/07/2023 03:35, Salil Mehta wrote: >>>>>> [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 >>>>> >>>>> The Realm exit with EXIT_PSCI already provides the parameters passed >>>>> onto the PSCI request. This happens for all PSCI calls except >>>>> (PSCI_VERSION and PSCI_FEAUTRES). The hyp could forward these exits to >>>>> the VMM and could invoke the RMI_PSCI_COMPLETE only when the VMM blesses >>>>> the request (wherever applicable). >>>>> >>>>> However, the RMM spec currently doesn't allow denying the request. >>>>> i.e., without RMI_PSCI_COMPLETE, the REC cannot be scheduled back in. >>>>> We will address this in the RMM spec and get back to you. >>>> >>>> This is now resolved in RMMv1.0-eac3 spec, available here [0]. >>>> >>>> This allows the host to DENY a PSCI_CPU_ON request. The RMM ensures that >>>> the response doesn't violate the security guarantees by checking the >>>> state of the target REC. >>>> >>>> [0] https://developer.arm.com/documentation/den0137/latest/ >>> >>> >>> Many thanks for taking this up proactively and getting it done as well >>> very efficiently. Really appreciate this! >>> >>> I acknowledge below new changes part of the newly released RMM >>> Specification [3] (Page-2) (Release Information 1.0-eac3 20-07-2023): >>> >>> 1. Addition of B2.19 PsciReturnCodePermitted function [3] (Page-126) >>> 2. Addition of 'status' in B3.3.7.2 Failure conditions of the >>> B3.3.7 RMI_PSCI_COMPLETE command [3] (Page-160) >>> >>> >>> Some Further Suggestions: >>> 1. It would be really helpful if PSCI_DENIED can be accommodated somewhere >>> in the flow diagram (D1.4.1 PSCI_CPU_ON flow) [3] (Page-297) as well. >> >> Good point, yes, will get that added. > > > Great. Thanks! > > >>> 2. You would need changes to handle the return value of the PSCI_DENIED >>> in this below patch [2] as well from ARM CCA series [1] >>> >> >> Of course. Please note that the series [1] is based on RMMv1.0-beta0 and >> we are in the process of rebasing our changes to v1.0-eac3, which >> includes a lot of other changes. The updated series will have all the >> required changes. > > > Ok. When are you planning to post this new series with v1.0-eac3 changes?
Please see :
https://lkml.kernel.org/r/42cbffac-05a8-a279-9bdb-f76354c1a1b1@arm.com
Suzuki
| |