x86/svm: Set IBRS value on VM entry and exit

x86/svm: Set IBRS value on VM entry and exit

CVE-2017-5715 (Spectre v2 Intel)

Set/restore the guests IBRS value on VM entry. On VM exit back to the
kernel save the guest IBRS value and then set IBRS to 1.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>