Re: early microcode: how to disable at runtime?
From: Henrique de Moraes Holschuh
Date: Sun Aug 31 2014 - 16:11:46 EST
On Sun, 31 Aug 2014, H. Peter Anvin wrote:
> On 08/31/2014 12:45 PM, Henrique de Moraes Holschuh wrote:
> > Currently, there is no way to disable early microcode update at runtime. If
> > an early initramfs with microcode update data is available, it will always
> > be used.
> > This can be a very big deal when things go wrong: it is hard for the regular
> > user to recover from an initramfs image that crashes the system, and the
> > early initramfs has no "disable" trigger.
> > In the general case, booting from rescue media will be required to fix the
> > system.
> > Unfortunately, the BSP microcode update is handled before early_param() is
> > available, so a kernel command line parameter to disable early microcode
> > updates for the BSP isn't easily possible.
> > Other than duplicating much of the code in parse_early_param/parse_args to
> > search for a "noearlymcu" parameter, is there any other way we could add a
> > disable switch for the early microcode update system?
> Probably more like something more like arch/x86/boot/cmdline.c. Maybe
> we could even make it sharable.
Looks like that would work, yes.
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