Known issues

Learn about known issues with Confidential VM. This topic discusses problems and errors whose resolutions require more steps than can be easily described in an error message. Additional workarounds and solutions may be found through a support channel.

Instances with more than 40 persistent disks

Confidential VM instances with more than 40 persistent disks (PDs) attached are not supported. If you need to attach more than 40 PDs, you can request an exception to this limitation through a support channel. Be aware that instances with more than 40 PDs may boot and fail silently.

Boot latency

Customers may notice longer boot times for Confidential VM instances with large amounts of memory. Boot time is proportional to the amount of memory assigned to an instance.

Disk naming

Due to a current limitation of NVME drivers, it is not possible to apply a customer-supplied device name to disks attached to a Confidential VM instance. If you need custom disk names as identifiers—for example, for automation purposes—as an example, a potential workaround is the use of the Compute Engine metadata service.

Formatting to XFS on persistent disks

Confidential VM instances do not support formatting existing persistent disks (PDs) to the XFS file system format at this time. You can create new PDs formatted as XFS.

I/O intensive workloads: increasing the size of the SWIOTLB

For disk and network input/output operations, Confidential VM uses a specific area in memory called the SWIOTLB, which has a default size of 64 MB. If you anticipate high levels of input/output on VMs with more than 8 vCPUs, increase the size of the SWIOTLB. The SWIOTLB is part of the total available RAM on the guest, so before increasing the size, be sure that the guest has an adequate amount of RAM for the SWIOTLB as well as the rest of the operating system.

For example, to increase the size of the SWIOTLB to 512 MB, append the following line to /etc/default/grub:

GRUB_CMDLINE_LINUX_DEFAULT=".... swiotlb=262144"

Then, regenerate grub.cfg by running the following commands:

Ubuntu

sudo update-grub

Other distros

grubcfg="/etc/grub2-efi.cfg"
cp $grubcfg $grubcfg.bak
grub2-mkconfig -o $grubcfg

For more information, see AMDSEV.