Messages in this thread | | | Date | Wed, 10 Jan 2018 12:33:07 +0100 | From | Borislav Petkov <> | Subject | Re: [patch RFC 1/5] x86/CPU: Sync CPU feature flags late |
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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.
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