AMD - emulate Extended CPUID Features override.

[araujo]

Summary

This patch comes from a PR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=224476
It looks right for me, but unfortunately I don't have any AMD FX now for testing.

Test Plan

Smoke test: build kernel on AMD Ryzen.
Run: Linux Fedora and FreeBSD HEAD as guest.

[rgrimes]

I am good with this too, other than it is not emulating it, it is just ignoring it by returning a 0, which may or may not have future implications.

[rgrimes]

Sorry for the extra noise here, I did not mean to accept it as bhvye, only me personally, so did delete/add bhyve umbrella to clear that bit.

[anish]

head/sys/amd64/vmm/amd/svm_msr.c

130

This cases could have been merged with upper block, something like

 case MSR_MTRR64kBase:
 case MSR_SYSCFG:
 case MSR_AMDK8_IPM:
case MSR_EXTFEATURES:
         *result = 0;
         break;

[araujo]

head/sys/amd64/vmm/amd/svm_msr.c

130

Thanks @anish , I made the changes at: https://svnweb.freebsd.org/changeset/base/339936