Re: [PATCH v10 00/43] arm64: Support for Arm CCA in KVM

[Steven Price <steven.price@arm.com>]

Hi Emi,

Many thanks for testing this!

Regards,
Steve

On 24/09/2025 03:34, Emi Kisanuki (Fujitsu) wrote:
> We tested this patch in our internal simulator which is a hardware simulator for Fujitsu's next generation CPU known as Monaka, and it produced the expected results.
> 
> I have verified the following
> 1. Launching the realm VM using Internal simulator -> Successfully launched by disabling MPAM support in the ID register.
> 2. Running kvm-unit-tests (with lkvm) -> All tests passed except for PMU (as expected, since PMU is not supported by the Internal simulator).[1]
> 
> Tested-by: Emi Kisanuki <fj0570is@fujitsu.com> [1] https://gitlab.arm.com/linux-arm/kvmEmi -unit-tests-cca cca/latest
> 
>> This series adds support for running protected VMs using KVM under the Arm
>> Confidential Compute Architecture (CCA).
>>
>> The related guest support was merged for v6.14-rc1 so you no longer need that
>> separately.
>>
>> There are a few changes since v9, many thanks for the review comments. The
>> highlights are below, and individual patches have a changelog.
>>
>>  * Fix a potential issue where the host was walking the stage 2 page tables on
>>    realm destruction. If the RMM didn't zero when undelegated (which it isn't
>>    required to) then the kernel would attempt to work the junk values and crash.
>>
>>  * Avoid RCU stall warnings by correctly settign may_block in
>>    kvm_free_stage2_pgd().
>>
>>  * Rebased onto v6.17-rc1.
>>
>> Things to note:
>>
>>  * The magic numbers for capabilities and ioctls have been updated. So
>>    you'll need to update your VMM. See below for the updated kvmtool branch.
>>
>>  * This series doesn't attempt to integrate with the guest-memfd changes that
>>    are being discussed (see below).
>>
>>  * Vishal raised an important question about what to do in the case of
>>    undelegate failures (also see below).
>>
>> guest-memfd
>> ===========
>>
>> This series still implements the same API as previous versions, which means only
>> the private memory of the guest is backed by guest-memfd, and the shared
>> portion is accessed using VMAs from the VMM. This approach is compatible with
>> the proposed changes to support guest-memfd backing shared memory but would
>> require the VMM to mmap() the shared memory at the appropriate time so that
>> KVM can access via the VMM's VMAs.
>>
>> Changing to access both shared and private through the guest-memfd API
>> shouldn't be difficult and could be done in a backwards compatible manner (with
>> the VMM choosing which method to use). It's not clear to me whether we want to
>> hold things up waiting for the full guest-memfd (and only support that
>> uAPI) or if it would be fine to just support both approaches and let VMM's switch
>> when they are ready.
>>
>> There is a slight wrinkle around the 'populate' uAPI
>> (KVM_CAP_ARM_RME_POPULATE). At the moment this expects 'double
>> mapping' - the contents to be populated should be in the shared memory region,
>> but the physical pages for the private region are also allocated from the
>> guest_memfd.
>> Arm CCA doesn't support a true 'in-place' conversion so this is required in some
>> form. However it may make sense to allow the populate call to take a user space
>> pointer for the data to be copied rather than require it to be in the shared memory
>> region. We do already have a "flags" argument so there's also scope for easily
>> supporting both options. The current approach integrates quite nicely in kvmtool
>> with the existing logic for setting up a normal
>> (non-CoCo) guest. But I'm aware kvmtool isn't entirely representative of what
>> VMMs do, so I'd welcome feedback on what a good populate uAPI would look like.
>>
>> Undelegation failure
>> ====================
>>
>> When the kernel is tearing down a CCA VM, it will attempt to "undelegate"
>> pages allowing them to be used by the Normal World again. Assuming no bugs
>> then these operations will always succeed. However, the RMM has the ability to
>> return a failure if it considers these pages to still be in use. A failure like this is
>> always a bug in the code, but it would be good to be able to handle these without
>> resorting to an immediate BUG_ON().
>>
>> The current approach in the code is to simply WARN() and use get_page() to take
>> an extra reference to the page to stop it being reused (as it will immediately cause
>> a GPF if the Normal World attempts to access the page).
>>
>> However this will cause problems when we start supporting huge pages. It may be
>> possible to use the HWPOISON infrastructure to flag the page as unusable
>> (although note there is no way of 'scrubbing' a page to recover from this situation).
>> The other option is to just accept this this "should never happen"
>> and upgrade the WARN() to a BUG_ON() so we don't have to deal with the
>> situation. A third option is to do nothing (other than WARN) and let the system run
>> until the inevitable GPF which will probably bring it down (and hope there's
>> enough time for the user to save work etc).
>>
>> I'd welcome thoughts on the best solution.
>>
>> ====================
>>
>> The ABI to the RMM (the RMI) is based on RMM v1.0-rel0 specification[1].
>>
>> This series is based on v6.17-rc1. It is also available as a git
>> repository:
>>
>> https://gitlab.arm.com/linux-arm/linux-cca cca-host/v10
>>
>> Work in progress changes for kvmtool are available from the git repository below:
>>
>> https://gitlab.arm.com/linux-arm/kvmtool-cca cca/v8
>>
>> [1] https://developer.arm.com/documentation/den0137/1-0rel0/
>>
>> Jean-Philippe Brucker (7):
>>   arm64: RME: Propagate number of breakpoints and watchpoints to
>>     userspace
>>   arm64: RME: Set breakpoint parameters through SET_ONE_REG
>>   arm64: RME: Initialize PMCR.N with number counter supported by RMM
>>   arm64: RME: Propagate max SVE vector length from RMM
>>   arm64: RME: Configure max SVE vector length for a Realm
>>   arm64: RME: Provide register list for unfinalized RME RECs
>>   arm64: RME: Provide accurate register list
>>
>> Joey Gouly (2):
>>   arm64: RME: allow userspace to inject aborts
>>   arm64: RME: support RSI_HOST_CALL
>>
>> Steven Price (31):
>>   arm64: RME: Handle Granule Protection Faults (GPFs)
>>   arm64: RME: Add SMC definitions for calling the RMM
>>   arm64: RME: Add wrappers for RMI calls
>>   arm64: RME: Check for RME support at KVM init
>>   arm64: RME: Define the user ABI
>>   arm64: RME: ioctls to create and configure realms
>>   KVM: arm64: Allow passing machine type in KVM creation
>>   arm64: RME: RTT tear down
>>   arm64: RME: Allocate/free RECs to match vCPUs
>>   KVM: arm64: vgic: Provide helper for number of list registers
>>   arm64: RME: Support for the VGIC in realms
>>   KVM: arm64: Support timers in realm RECs
>>   arm64: RME: Allow VMM to set RIPAS
>>   arm64: RME: Handle realm enter/exit
>>   arm64: RME: Handle RMI_EXIT_RIPAS_CHANGE
>>   KVM: arm64: Handle realm MMIO emulation
>>   arm64: RME: Allow populating initial contents
>>   arm64: RME: Runtime faulting of memory
>>   KVM: arm64: Handle realm VCPU load
>>   KVM: arm64: Validate register access for a Realm VM
>>   KVM: arm64: Handle Realm PSCI requests
>>   KVM: arm64: WARN on injected undef exceptions
>>   arm64: Don't expose stolen time for realm guests
>>   arm64: RME: Always use 4k pages for realms
>>   arm64: RME: Prevent Device mappings for Realms
>>   arm_pmu: Provide a mechanism for disabling the physical IRQ
>>   arm64: RME: Enable PMU support with a realm guest
>>   arm64: RME: Hide KVM_CAP_READONLY_MEM for realm guests
>>   KVM: arm64: Expose support for private memory
>>   KVM: arm64: Expose KVM_ARM_VCPU_REC to user space
>>   KVM: arm64: Allow activating realms
>>
>> Suzuki K Poulose (3):
>>   kvm: arm64: Include kvm_emulate.h in kvm/arm_psci.h
>>   kvm: arm64: Don't expose debug capabilities for realm guests
>>   arm64: RME: Allow checking SVE on VM instance
>>
>>  Documentation/virt/kvm/api.rst       |   92 +-
>>  arch/arm64/include/asm/kvm_emulate.h |   38 +
>>  arch/arm64/include/asm/kvm_host.h    |   13 +-
>>  arch/arm64/include/asm/kvm_rme.h     |  135 ++
>>  arch/arm64/include/asm/rmi_cmds.h    |  508 ++++++++
>>  arch/arm64/include/asm/rmi_smc.h     |  269 ++++
>>  arch/arm64/include/asm/virt.h        |    1 +
>>  arch/arm64/include/uapi/asm/kvm.h    |   49 +
>>  arch/arm64/kvm/Kconfig               |    1 +
>>  arch/arm64/kvm/Makefile              |    2 +-
>>  arch/arm64/kvm/arch_timer.c          |   44 +-
>>  arch/arm64/kvm/arm.c                 |  169 ++-
>>  arch/arm64/kvm/guest.c               |  108 +-
>>  arch/arm64/kvm/hypercalls.c          |    4 +-
>>  arch/arm64/kvm/inject_fault.c        |    5 +-
>>  arch/arm64/kvm/mmio.c                |   16 +-
>>  arch/arm64/kvm/mmu.c                 |  209 ++-
>>  arch/arm64/kvm/pmu-emul.c            |    6 +
>>  arch/arm64/kvm/psci.c                |   30 +
>>  arch/arm64/kvm/reset.c               |   23 +-
>>  arch/arm64/kvm/rme-exit.c            |  207 +++
>>  arch/arm64/kvm/rme.c                 | 1746
>> ++++++++++++++++++++++++++
>>  arch/arm64/kvm/sys_regs.c            |   53 +-
>>  arch/arm64/kvm/vgic/vgic-init.c      |    2 +-
>>  arch/arm64/kvm/vgic/vgic.c           |   61 +-
>>  arch/arm64/mm/fault.c                |   31 +-
>>  drivers/perf/arm_pmu.c               |   15 +
>>  include/kvm/arm_arch_timer.h         |    2 +
>>  include/kvm/arm_pmu.h                |    4 +
>>  include/kvm/arm_psci.h               |    2 +
>>  include/linux/perf/arm_pmu.h         |    5 +
>>  include/uapi/linux/kvm.h             |   29 +-
>>  32 files changed, 3778 insertions(+), 101 deletions(-)  create mode 100644
>> arch/arm64/include/asm/kvm_rme.h  create mode 100644
>> arch/arm64/include/asm/rmi_cmds.h  create mode 100644
>> arch/arm64/include/asm/rmi_smc.h  create mode 100644
>> arch/arm64/kvm/rme-exit.c  create mode 100644 arch/arm64/kvm/rme.c
>>
>> --
>> 2.43.0
>