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

Emi Kisanuki (Fujitsu)
2025-09-24T02:35:46Z

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