I'm using a Thinkpad T440p with Samsung 840 Pro SSD. I set the hard drive password in the bios, so that everytime the laptop boots from cold, one needs to enter the password first.

Now when Windows reboots the password does not need to be re-entered, which is the expected behavior, as the password is only requested when the hard drive loses power.

When Linux reboots the laptop gets to the Thinkpad logo (which is before the password prompt screen) and then just shuts off. (Same behavior when restarting from Mac OS X)

On the other hand it works when restarting somewhere early in the boot process or from some OS installation with Ctrl-Alt-Del. That looks to me like the problem is that Linux somehow turns off the hard drive, which then forgets the password, which is why the BIOS turns off when attempting to restart, to bring up the password dialogue.

Does anyone have any experience with this or suggestions how to fix this? It would be nice to be able to switch between Linux and Windows very quickly.

Is the harddrive actually fully encrypted or is the password simply preventing boot?

That depends how the Samsung drive implements ATA passwords. Samsung SSDs (or at least this model) always encrypt the memory, but simply store the key. Ideally the ATA password is implemented so that it is used to decrypt the encryption key, but who knows.

But how do you think does that make a difference?

It would be silly to depend on a boot password that doesn't provide full disk encryption. There are plenty of Linux solutions for full disk encryption. It doesn't sound like disk encryption if you don't need to enter a key on reboot which is why I asked.

It's hardware based, why would you need to enter the password again? The drive remembers the password until you turn it off.

But you're right this is definitely not 100% secure and my important data is additionally encrypted with dm-crypt.

However my original question wasn't about security, I just wonder how I can make the drive not power off when Linux is shut down (if that's what's causing the reboot problem). There must be a way, since it works fine in Windows.