When nested virtualization is in use, VMENTER operations from the nested
hypervisor into the nested guest will always be processed by the bare metal
hypervisor, and KVM's "conditional cache flushes" mode in particular does a
flush on nested vmentry.  Therefore, include the "skip L1D flush on
vmentry" bit in KVM's suggested ARCH_CAPABILITIES setting.

Add the relevant Documentation.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

CVE-2018-3620
CVE-2018-3646

[tyhicks: Adjust for the missing MSR_F10H_DECFG and MSR_IA32_UCODE_REV
 feature MSRs which do not exist in 4.15]
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
[smb: Minor context and adjusted documentation path]
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>