x86/bugs, kvm: don't miss SSBD when IBRS is in use.

x86/bugs, kvm: don't miss SSBD when IBRS is in use.

When IBRS is in use, we unconditionnaly need to write to MSR_IA32_SPEC_CTRL
(it acts as a barrier) but we were failing to take into account the SSBD
state from the thread info flags, potentially disabling SSBD on the host on
tasks that needs it after a vmexit.

Orabug: 29642113

Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>