x86/pv: Don't deliver #GP for a SYSENTER with NT set

x86/pv: Don't deliver #GP for a SYSENTER with NT set

It is a matter of guest kernel policy what to do with offending userspace, and
terminating said userspace may not be the action chosen.

Linux explicitly tolerates this case.

Reported-by: Andy Lutomirski <luto@kernel.org>
Fixes: fdac951560 ("x86: clear EFLAGS.NT in SYSENTER entry path")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 61d4a04349895edc5a5868274b906ba61ef24f47
master date: 2020-09-24 21:02:35 +0100