Draft: x86/bugs: Extend VMware Retbleed workaround to Nehalem & earlier CPUs

JIRA: https://issues.redhat.com/browse/RHEL-48649
Upstream Status: RHEL only

To address the incorrect ARCH_CAP_RSBA bit set by VMware hypervisor, a retbleed_whitelist[] was introduced in RHEL only commit 890c3066 ("x86/bugs: Workaround for incorrectly set X86_BUG_RETBLEED under VMware") to work around incorrect activation of IBRS which could have some noticeable performance impact. As it was a Westmere CPU that was having this problem at the time, the whitelist included Westmere and all the follow-on CPUs before Skylake.

Now it is reported that some Nehalem using customers also have the same problem. Extend the retbleed_whitelist[] to include all the Intel FAM6 processors before Skylake as well to prevent them from being marked as vulnerable to Retbleed.

Signed-off-by: Waiman Long longman@redhat.com