x86/KVM/VMX: Extend add_atomic_switch_msr() to allow VMENTER only MSRs

x86/KVM/VMX: Extend add_atomic_switch_msr() to allow VMENTER only MSRs

The IA32_FLUSH_CMD MSR needs only to be written on VMENTER. Extend
add_atomic_switch_msr() with an entry_only parameter to allow storing the
MSR only in the guest (ENTRY) MSR array.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
CVE-2018-3620
CVE-2018-3646

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>