lkml.org 
[lkml]   [2018]   [Jan]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [patch RFC 1/5] x86/CPU: Sync CPU feature flags late
    On Wed, Jan 10, 2018 at 07:20:13AM +0100, Ingo Molnar wrote:
    > it be really unreasonable to say that if a microcode update changes CPU
    > flags an initrd rebuild and a reboot is required? It's not like microcode updates
    > are _that_ frequent - in fact they tend to be much _less_ frequent in a system's
    > life time than kernel updates.
    >
    > So all of this 'late loading' and CPU flag splitting complexity seems unnecessary
    > to me: we should be glad we do early microcode loading now, and should embrace it.
    >
    > Changing CPU features way after the CPU has booted up is possible, and we could in
    > theory extend code patching to work 'late' as well, but given how infrequent all
    > this is bound to be in practice I fear it's all going to be a big, seldom tested,
    > often broken mess, with no real benefit to users.

    Agreed: we support that late patching for those use cases where machines
    run for a long time, simulating all kinds of crap. And frankly, if
    those things need to get IBRS all of a sudden and *not* reboot, then
    something's wrong with the whole contraption setup.

    So yes, I'd vote too for supporting only early IBRS and not do the late
    thing now. Maybe later, if there's, like, a really compelling use case.

    I will have to do the late thing for our old kernels which don't have
    early loading but that would be a one-off and my problem.

    --
    Regards/Gruss,
    Boris.

    Good mailing practices for 400: avoid top-posting and trim the reply.

    \
     
     \ /
      Last update: 2018-01-14 23:21    [W:3.398 / U:0.024 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site