KVM: Fix segment descriptor loading

KVM: Fix segment descriptor loading

commit c697518a861e6c43b92b848895f9926580ee63c3 upstream

Add proper error and permission checking. This patch also change task
switching code to load segment selectors before segment descriptors, like
SDM requires, otherwise permission checking during segment descriptor
loading will be incorrect.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>