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

Gavin Shan
2025-09-04T00:47:13Z

On 8/21/25 12:55 AM, Steven Price wrote:
> 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).
>

[...]

I tried to boot a guest using the following combinations, nothing obvious went to
wrong except several long existing issues (described below). So feel free to add:

Tested-by: Gavin Shan <gshan@redhat.com>

Combination
===========
host.tf-a https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git (v2.13-rc0)
host.tf-rmm https://git.codelinaro.org/linaro/dcap/rmm (cca/v8)
host.edk2 git@github.com:tianocore/edk2.git (edk2-stable202411)
host.kernel git@github.com:gwshan/linux.git (cca/host-v10) (this series)
host.qemu https://git.qemu.org/git/qemu.git (stable-9.2)
host.buildroot https://github.com/buildroot/buildroot (master)
guest.qemu https://git.codelinaro.org/linaro/dcap/qemu.git (cca/latest) (with linux-headers sync'ed)
guest.kvmtool https://gitlab.arm.com/linux-arm/kvmtool-cca (cca/latest)
guest.edk2 https://git.codelinaro.org/linaro/dcap/edk2 (cca/latest)
guest.kernel git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git (v6.17.rc3)
guest.buildroot https://github.com/buildroot/buildroot (master)

Script to start the host
========================
gshan@nvidia-grace-hopper-01:~/sandbox/qemu/host$ cat start.sh
#!/bin/sh
HOST_PATH=/home/gshan/sandbox/qemu/host
GUEST_PATH=/home/gshan/sandbox/qemu/guest
IF_UP_SCRIPT=/etc/qemu-ifup-gshan
IF_DOWN_SCRIPT=/etc/qemu-ifdown-gshan

sudo ${HOST_PATH}/qemu/build/qemu-system-aarch64 \
-M virt,virtualization=on,secure=on,gic-version=3,acpi=off \
-cpu max,x-rme=on -m 3G -smp 8 \
-serial mon:stdio -monitor none -nographic -nodefaults \
-bios ${HOST_PATH}/tf-a/flash.bin \
-kernel ${HOST_PATH}/linux/arch/arm64/boot/Image \
-initrd ${HOST_PATH}/buildroot/output/images/rootfs.cpio.xz \
-device pcie-root-port,bus=pcie.0,chassis=1,id=pcie.1 \
-device pcie-root-port,bus=pcie.0,chassis=2,id=pcie.2 \
-device pcie-root-port,bus=pcie.0,chassis=3,id=pcie.3 \
-device pcie-root-port,bus=pcie.0,chassis=4,id=pcie.4 \
-device virtio-9p-device,fsdev=shr0,mount_tag=shr0 \
-fsdev local,security_model=none,path=${GUEST_PATH},id=shr0 \
-netdev tap,id=tap1,script=${IF_UP_SCRIPT},downscript=${IF_DOWN_SCRIPT} \
-device virtio-net-pci,bus=pcie.2,netdev=tap1,mac=b8:3f:d2:1d:3e:f1

Script to start the guest
=========================
gshan@nvidia-grace-hopper-01:~/sandbox/qemu/guest$ cat start_full.sh
#!/bin/sh
key="VGhlIHJlYWxtIGd1ZXN0IHBlcnNvbmFsaXphdGlvbiBrZXkgaW4gZm9ybWF0IG9mIGJhc2U2NCAgICAgICAgIA=="
IF_UP_SCRIPT=/etc/qemu-ifup
IF_DOWN_SCRIPT=/etc/qemu-ifdown

qemu-system-aarch64 -enable-kvm \
-object rme-guest,id=rme0,measurement-algorithm=sha512,personalization-value=${key} \
-M virt,gic-version=3,confidential-guest-support=rme0 \
-cpu host -smp 4 -m 2G -boot c \
-serial mon:stdio -monitor none -nographic -nodefaults \
-bios /mnt/edk2/Build/ArmVirtQemu-AARCH64/RELEASE_GCC5/FV/QEMU_EFI.fd \
-device pcie-root-port,bus=pcie.0,chassis=1,id=pcie.1 \
-device pcie-root-port,bus=pcie.0,chassis=2,id=pcie.2 \
-drive file=/mnt/rhel10.qcow2,if=none,id=drive0 \
-device virtio-blk-pci,id=virtblk0,bus=pcie.1,drive=drive0,num-queues=4 \
-netdev tap,id=tap0,script=${IF_UP_SCRIPT},downscript=${IF_DOWN_SCRIPT} \
-device virtio-net-pci,bus=pcie.2,netdev=tap0,mac=b8:3f:d2:1d:3e:f9

Issues
======
1. virtio-iommu isn't supported by QEMU. The guest kernel becomes stuck at IOMMU
probing time where the endpoint's capabilities is queried by sending request over
virtio device's vring and the response is expected to be fed by QEMU. The request
can't be seen by QEMU due to the wrong IOMMU address translation used in QEMU as
virtio-iommu provides a different IOMMU address translation operations to override
the platform one, leading the DMA address (in the shared space) can't be properly
recognized. The information has been shared to Jean.

2. 'reboot' command doesn't work in the guest. QEMU complains some registers aren't
accessible from QEMU. I didn't sorted out a workaround for this.

3. HMP command 'dump-guest-memory' causes QEMU to exit abnormally. The cause is the
realm is reconfigured when the VM is resumed after the guest memory is dumped. The
reconfiguration is rejected by the host, leading QEMU's abnormal exit. The fix would
be to avoid the reconfiguration on the realm. The issue was originally reported by
Fujitsu and all the information has been shared to Fujitsu.

4. In QEMU, the CPU property 'kvm-no-adjvtime' can't be set to off. Otherwise, QEMU
tries to access the timer registers, which have been hidden by the host. So we need
to take the parameter (for QEMU) to by pass it: "-cpu host,kvm-no-adjvtime=on".

5. I didn't try virtio-mem and memory balloon, which isn't expected to work, especially
when the guest memory is hot added or hot removed.

Thanks,
Gavin