Re: [PATCH] x86: Unbreak early processor microcode loading

[Daniel J Blueman]

On 04/03/2015 00:38, Borislav Petkov wrote:
> On Tue, Mar 03, 2015 at 11:10:44PM +0800, Daniel J Blueman wrote:
> > The changes in 871b72dd "x86: microcode: use smp_call_function_single instead
> > of set_cpus_allowed, cleanup of synchronization logic" introduced a check
> > that prevents built-in microcode from being loaded before init starts.
> >
> > Conditionalise it on early microcode loading, so we get the expected behaviour
> > when early microcode loading is enabled, and when it is not. This has potential
> > importance as BIOSes often don't load the current microcode.
>
> ... probably because they don't have it. Which is also the main reason
> for the existence of this microcode loader btw :)
>
> > Signed-off-by: Daniel J Blueman <daniel@xxxxxxxxxxxxx>
> > ---
> >   arch/x86/kernel/cpu/microcode/core.c | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
> > index 36a8361..fa7f9fc 100644
> > --- a/arch/x86/kernel/cpu/microcode/core.c
> > +++ b/arch/x86/kernel/cpu/microcode/core.c
> > @@ -391,9 +391,11 @@ static enum ucode_state microcode_init_cpu(int cpu, bool refresh_fw)
> >   	if (collect_cpu_info(cpu))
> >   		return UCODE_ERROR;
> >
> > +#if !defined(CONFIG_MICROCODE_AMD_EARLY) && !defined(CONFIG_MICROCODE_INTEL_EARLY)
> >   	/* --dimm. Trigger a delayed update? */
> >   	if (system_state != SYSTEM_RUNNING)
> >   		return UCODE_NFOUND;
> > +#endif
>
> Ok, let me try to understand this correctly: where is this microcode
> built in, into the kernel?
>
> If yes, you should consider enabling the early loading
> method and build in the microcode into the initrd, see
> Documentation/x86/early-microcode.txt
>
> This is the preferred method as we're applying the microcode much
> earlier.
>
> Back to you.

Yes, it's built into the kernel with config:

CONFIG_FIRMWARE_IN_KERNEL=y
CONFIG_EXTRA_FIRMWARE="amd-ucode/microcode_amd.bin 
amd-ucode/microcode_amd_fam15h.bin"
CONFIG_EXTRA_FIRMWARE_DIR="../firmware"

That's as some customer and in-house environments we use are 
initramfs-less and some we don't have direct control over the initramfs.

I don't see why built-in microcode loading shouldn't work, so I guess 
the question is, why was that 'system_state .. RUNNING' check introduced?

If just a cleanup and loading built-in microcode early was overlooked, 
it may be reasonable to conditionalise the check like so.

Thanks,
  Daniel
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