If you try to log in at http://en.wikipedia.beta-hhvm.wmflabs.org/w/index.php?title=Special:UserLogin&returnto=Main+Page, you get: "Login error: Wikipedia uses cookies to log in users. You have cookies disabled. Please enable them and try again." This is despite the fact that HHVM-powered wikis map loginwiki to loginwiki.wikimedia.beta-hhvm URLs, and the cookies that it sets appear to have the right domain.
Version: unspecified
Severity: critical
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=68044