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SubjectQuery regarding Spectre fixes - IBRS/IBPB/SSB...

I have been tracking Spectre related fixes at Linux kernel 4.4.x LTS branch, for some of our products on this kernel version.

One thing I noted is, some kernel fixes are added at upstream kernels 4.16 and 4.17, related to IBRS/IBPB capabilities and SSB fix.
Few of the related commits listed below:

    x86/speculation: Use synthetic bits for IBRS/IBPB/STIBP

    x86/speculation: Add basic IBPB (Indirect Branch Prediction Barrier) support
    Expose indirect_branch_prediction_barrier() for use in subsequent patches.

    x86/speculation: Use IBRS if available before calling into firmware

These changes are not seen backported to 4.4.* LTS. Have few related queries:

1. Is a microcode update of IBRS/IBPB/SSB fixes alone good enough for cover from the vulnerabilities.
2. Are the kernel changes as above a must to utilize IBRS/IBPB against Spectre vulnerabilities.?
3. Is there a plan to back port above fixes to 4.4.* LTS branch?.


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