Messages in this thread | | | Date | Wed, 10 Jan 2018 12:02:54 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [patch RFC 1/5] x86/CPU: Sync CPU feature flags late |
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On Tue, 9 Jan 2018, Andy Lutomirski wrote: > > On Jan 9, 2018, at 5:47 PM, Thomas Gleixner <tglx@linutronix.de> wrote: > > > > On Wed, 10 Jan 2018, Van De Ven, Arjan wrote: > >>> In other words, if you use late microcode loading for getting IBRS, you > >>> don't get ALTERNATIVE patching and its benefits? > >>> > >>> I'll also profess some microcode ignorance here. Is "late microcode > >>> patching" *all* of the stuff we do from the OS, or do we have early and > >>> late Linux loading in addition to what the BIOS can do? > >> > >> the early boot loader level stuff is much better generally (but does not > >> work when the microcode comes out after the system booted... like really > >> long uptimes) > > > > That stuff indeed would be way simpler w/o the late support, but the fact > > that the microcode for this might reach the user way later than the kernel > > support makes it almost a must to support the late loading. >
> How hard would it be to add a late alternative feature? Concretely, we'd > have a list of "late" cpufeatures. When we scan the alternative list, if > we find a late feature, we copy it to some other list that isn't > discarded, and we also copy its replacement (and relocate it eagerly, > since we'll lose the offset).
It shouldn't be rocket science, but that's not for now. And yes, we should do it.
Thanks,
tglx
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