On 27/07/2023 15:24, Salil Mehta wrote:
Hi Suzuki,
From: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
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@xxxxxxx>
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@xxxxxxx
Suzuki
