Inspiron 3493 Windows 10 Home Device Encryption unavailable

Hi all,

Our company has several Dell Inspiron 3493s (amongst other devices, but this model is our most common) running Windows 10 Home. I joined only recently but as far as I can tell, all of these devices came with Windows 10 Home Device Encryption enabled by default/out of the box.

I've just been re-purposing one for a new user and noticed that the "Device encryption settings" menu was totally missing. At first I thought it was a TPM issue, but TPM shows as enabled (in PowerShell via Get-TPM) and reporting normally.

After some searching, I discovered that System Information->System Summary->Device Encryption Support has the message:

"Reasons for failed automatic device encryption: Un-allowed DMA capable bus/device(s) detected."

Microsoft have this page which explains the error ("Windows detected at least one potential external DMA capable bus or device that may expose a DMA threat"), and says "To resolve this issue, contact the IHV(s) to determine if this device has no external DMA ports."

I'm not sure what this bus or device could be, but the article goes on to explain how to allow them. I have no idea how to identify what the "detected device" is (if any?!) to add it to the allow list.

Just to see if it worked, I removed everything from the blocklist key mentioned in the article (HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\DmaSecurity\Default\UnallowedBuses). After a reboot, the message in System Information is gone and Device Encryption is now available.

Turned on Device Encryption, reset the state of the \UnallowedBuses key, rebooted again, and it all seems to be there. `manage-bde` reports the encryption is enabled on the C:.

Disabling Device Encryption and rebooting restores it to original "broken" state with Device Encryption no longer available.

I have opened a support case with Dell about this and (perhaps unsurprisingly) after the usual diagnostics, they told me it's an OS problem and to go talk to Microsoft.

Before I go down this rabbit hole I was hoping to check if anyone out there in Dell-land had a Windows 10 Home system that they may have recently re-installed to see if Device Encryption is no longer available when it may have been previously? I am wondering if this is the side effect of a recent OS update, or a recent Dell driver update, that may be impacting systems that were working normally.

Thanks for any suggestions.