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    SubjectRe: [PATCH] x86/apic: Don't disable x2APIC if locked
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    On 8/10/22 11:30, Daniel Sneddon wrote:
    >> If it's going to be on one server CPU that's coming out in ten years,
    >> then we can hold off.
    > SPR will certainly be sooner than 10 years, and with distros running on LTS
    > kernels, it is probably worth backporting. Since this isn't a bug fix (not a sw
    > bug anyway), is this something I can just CC stable or is there a better way to
    > say "Yes, this is a new feature, BUT, you really want it anyway"?

    It it going to be *forced* on those SPR system? In other words, is it a
    little BIOS switch that users can flip? Is there any non-kernel
    workaround if a user hits this, or is the entire burden of this going to
    be foisted on the kernel?

    The worst case scenario would be if a user has managed to compile a
    CONFIG_X86_X2APIC=n kernel and is happily running along until they get a
    microcode update, reboot and can't boot any more.

    A less-bad, but still nasty situation would be someone who is booting
    with nox2apic, who also suddenly loses the ability to boot until they
    figure out why their kernel is #GP'ing and oopsing early in boot and
    remove nox2apic.

    I think we need a bit more information on how this thing will get
    deployed before we really know if it needs to be in stable kernels or
    not. For instance, if Intel really views this as an always-on security
    mitigation, that's a different story than if this is, say, a performance
    tweak.

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