Ignore the write to AMD microcode update MSR by guest.

[anish]

Summary

If a guest try to update microcode register, don't fail it but silently drop the write.
Submitted by: Yamagi Burmeister

Test Plan

Tested on Ubuntu VM by writing to this MSR[0xc0010020].

[grehan]

Fix up the plurality a bit in the checkin comment e.g. "If a guest tries to update the microcode register" and it's good to go :)

[anish]

Ignore the write to AMD microcode update MSR by guest.

Summary: Allow guest writes to AMD microcode update[0xc0010020] MSR without updating actul hardware MSR. This allows guest microcode update to go through which otherwise failing because wrmsr() was returning EINVAL.

Submitted by: Yamagi Burmeister

Test Plan: Tested on Ubuntu VM by writing to this MSR[0xc0010020].

Reviewers: neel, grehan

Subscribers:

[anish]

Was submitted by r297806