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    SubjectRe: [Patch v3 Part2 3/9] x86/microcode/intel: Fix collect_cpu_info() to reflect current microcode
    On Wed, Feb 01, 2023 at 11:13:58AM -0800, Dave Hansen wrote:
    > On 1/30/23 13:39, Ashok Raj wrote:
    > > Currently collect_cpu_info() is only returning what was cached earlier
    > > instead of reading the current revision from the proper MSR.
    > >
    > > Collect the current revision and report that value instead of reflecting
    > > what was cached in the past.
    > >
    > > [TBD:
    > > Need to change microcode/amd.c. I didn't quite follow the logic since
    > > it reports the revision from the patch file, instead of reporting the
    > > real PATCH_LEVEL MSR.
    > >
    > > Untested on AMD.
    > > ]
    >
    > This thread is meandering a bit. I think it's because this changelog
    > doesn't have a problem statement. It's hard to agree on a patch being a
    > solution to anything if we haven't first agreed on the problem.
    >
    > What is the problem?

    I alluded here.. But yes, clearly missed in the commit log.

    https://lore.kernel.org/lkml/Y9mW7EiL%2FBpYFLWn@a4bf019067fa.jf.intel.com/

    Thomas alluded here https://lore.kernel.org/lkml/87y1pygiyf.ffs@tglx/
    that error handling in __reload_late()::wait_for_siblings() code patch is
    completely broken.

    This is one that I "assumed" he was referring to, since all we need is to
    update the current revision, but we end up depending on the behavior of
    apply_microcode() and that might accidentally have some side effects.

    Instead only call the collect_cpu_info() and allow that to update the
    per-cpu revision instead. And there is no risk in performing that vs
    accidentally letting it fall through with an apply_microcode() that might
    have risks.

    >
    > What does this "fix"?

    The code performs this delicate late-load dance to prevent sibling threads
    to be quiet while performing the update.

    At wait_for_siblings() when all threads arrive, then the sibling does the
    apply_microcode() which seems wrong.


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