[raverbashing]

That's very interesting. I guess VRAM doesn't get powered off during reboot and (today) it is huge, so the chance of interesting information remaining is big.

Mitigation strategy: Ctrl-Alt-F1 and work in text mode. (or just fill up video ram doing stuff in your machine after doing the sensitive work)

[Ciantic]

Best mitigation strategy is not to share VRAM by disabling 3d acceleration with Guests you absolutely don't want to snoop on your host pixels.

[raverbashing]

That takes care of the "Guest snooping on the Host" case, but not the case of physical attack on the machine.