KVM: x86: Add a framework for supporting MSR-based features

KVM: x86: Add a framework for supporting MSR-based features

Provide a new KVM capability that allows bits within MSRs to be recognized
as features.  Two new ioctls are added to the /dev/kvm ioctl routine to
retrieve the list of these MSRs and then retrieve their values. A kvm_x86_ops
callback is used to determine support for the listed MSR-based features.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[Tweaked documentation. - Radim]
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
CVE-2018-3620
CVE-2018-3646

(backported from commit 801e459a6f3a63af9d447e6249088c76ae16efc4)
[tyhicks: Adjust context for missing mem_enc_* kvm_x86_ops]
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>