x86, kaiser, xen: Dynamically disable KAISER when running under Xen PV

From: Dave Hansen <dave.hansen@linux.intel.com>

If you paravirtualize the MMU, you can not use KAISER.  This boils down
to the fact that KAISER needs to do CR3 writes in places that it is not
feasible to do real hypercalls.

If Xen PV is detected to be in use, do not do the KAISER CR3 switches.

I don't think this too bug of a deal for Xen.  I was under the
impression that the Xen guest kernel and Xen guest userspace didn't
share an address space *anyway* so Xen PV is not normally even exposed
to the kinds of things that KAISER protects against.

This allows KAISER=y kernels to deployed in environments that also
require PARAVIRT=y.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Juergen Gross <jgross@suse.com>
Cc: Moritz Lipp <moritz.lipp@iaik.tugraz.at>
Cc: Daniel Gruss <daniel.gruss@iaik.tugraz.at>
Cc: Michael Schwarz <michael.schwarz@iaik.tugraz.at>
Cc: Richard Fellner <richard.fellner@student.tugraz.at>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kees Cook <keescook@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: x86@kernel.org
2 files changed