arm64: KVM: Add HYP per-cpu accessors

arm64: KVM: Add HYP per-cpu accessors

BugLink: https://bugs.launchpad.net/bugs/1787993
CVE-2018-3639 (arm64)

commit 85478bab409171de501b719971fd25a3d5d639f9 upstream.

As we're going to require to access per-cpu variables at EL2,
let's craft the minimum set of accessors required to implement
reading a per-cpu variable, relying on tpidr_el2 to contain the
per-cpu offset.

Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 0592871918f0acf369cec5c88de1fa76dbf2c1a2
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git /
linux-4.14.y)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>