++
+If this does not return empty your host's CPU has support for 'pcid'.
+
+* 'spec-ctrl'
++
+Required to enable the Spectre v1 (CVE-2017-5753) and Spectre v2 (CVE-2017-5715) fix,
+in cases where retpolines are not sufficient.
+Included by default in Intel CPU models with -IBRS suffix.
+Must be explicitly turned on for Intel CPU models without -IBRS suffix.
+Requires an updated host CPU microcode (intel-microcode >= 20180425).
++
+* 'ssbd'
++
+Required to enable the Spectre V4 (CVE-2018-3639) fix. Not included by default in any Intel CPU model.
+Must be explicitly turned on for all Intel CPU models.
+Requires an updated host CPU microcode(intel-microcode >= 20180703).
+
+
+AMD processors
+^^^^^^^^^^^^^^
+
+* 'ibpb'
++
+Required to enable the Spectre v1 (CVE-2017-5753) and Spectre v2 (CVE-2017-5715) fix,
+in cases where retpolines are not sufficient.
+Included by default in AMD CPU models with -IBPB suffix.
+Must be explicitly turned on for AMD CPU models without -IBPB suffix.
+Requires the host CPU microcode to support this feature before it can be used for guest CPUs.
+
+
+
+* 'virt-ssbd'
++
+Required to enable the Spectre v4 (CVE-2018-3639) fix.
+Not included by default in any AMD CPU model.
+Must be explicitly turned on for all AMD CPU models.
+This should be provided to guests, even if amd-ssbd is also provided, for maximum guest compatibility.
+Note that this must be explicitly enabled when when using the "host" cpu model,
+because this is a virtual feature which does not exist in the physical CPUs.
+
+
+* 'amd-ssbd'
++
+Required to enable the Spectre v4 (CVE-2018-3639) fix.
+Not included by default in any AMD CPU model. Must be explicitly turned on for all AMD CPU models.
+This provides higher performance than virt-ssbd, therefore a host supporting this should always expose this to guests if possible.
+virt-ssbd should none the less also be exposed for maximum guest compatibility as some kernels only know about virt-ssbd.
+
+
+* 'amd-no-ssb'
++
+Recommended to indicate the host is not vulnerable to Spectre V4 (CVE-2018-3639).
+Not included by default in any AMD CPU model.
+Future hardware generations of CPU will not be vulnerable to CVE-2018-3639,
+and thus the guest should be told not to enable its mitigations, by exposing amd-no-ssb.
+This is mutually exclusive with virt-ssbd and amd-ssbd.