On 12/3/24 2:58 AM, Yuvaraj Ranganathan wrote:
Hi Everyone, We are trying to launch a VM’s using qemu with TPM passthrough (https://www.qemu.org/docs/master/specs/tpm.html) and we are encountering the QEMU launch is failing on below experiments, Problem 1: qemu-system-aarch64 \ -M virt -m 2G \ -tpmdev passthrough,id=tpm0,path=/dev/tpmrm0 -device tpm-tis,tpmdev=tpm0 \ -kernel /mnt/overlay/Image \ -drive file=/mnt/overlay/qcom-guestvm-image-qcs9100-ride-sx-20241118050754.rootfs.ext4,if=virtio,format=raw \ -append "root=/dev/vda" \ -cpu host --enable-kvm -smp 4 -nographic qemu-system-aarch64: -tpmdev passthrough,id=tpm0,path=/dev/tpmrm0: tpm_passthrough: Could not guess TPM cancel path Problem 2: (experimented based on open source discussions) qemu-system-aarch64 \ -M virt -m 2G \ -tpmdev passthrough,id=tpm0,path=/dev/tpmrm0,cancel-path=/sys/class/tpm/tpm0/device/cancel -device tpm-tis,tpmdev=tpm0 \ -kernel /mnt/overlay/Image \ -drive file=/mnt/overlay/qcom-guestvm-image-qcs9100-ride-sx-20241118050754.rootfs.ext4,if=virtio,format=raw \ -append "root=/dev/vda" \ -cpu host --enable-kvm -smp 4 -nographic qemu-system-aarch64: -tpmdev passthrough,id=tpm0,path=/dev/tpmrm0,cancel-path=/sys/class/tpm/tpm0/device/cancel: tpm_passthrough: Could not open TPM cancel path: No such file or directory
A possibility is to pass /dev/null in this case. When we start VMs like with passthrough in libvirt then we also pass /dev/null if the cancel sysfs file cannot be found (anymore):
https://github.com/libvirt/libvirt/blob/dba710374d92688f797bf64642cc0d640c301239/src/util/virtpm.c#L67-L93
On further checking, it is due to /sys/class/tpm/tpm0/device/cancel attribute is not created by TPM driver. Temporary Solution explored: We made the change in TPM driver to use tpm1_dev_group irrespective of TPM version. tpm2_dev_group is creating only tpm_version_major attribute while tpm1_dev_group is creating multiple attributes including cancel + tpm2 attributes. With this change, we are able to launch VM’s successfully using QEMU command. TPM HW version: 2.0 QEMU emulator version: 6.2.0 This seems to be basic issue with QEMU + TPM 2.0 HW. Could you please help us know are we missing any procedure in the QEMU steps ? If the procedure is good, I shall go ahead to post an upstream patch with the fix. Need your comments here!!! Thanks, Yuvaraj.
