linux-kernel - Re: [PATCH] x86: Unbreak early processor microcode loading

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Date:	Tue, 3 Mar 2015 17:38:37 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Daniel J Blueman <daniel@...ascale.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Quentin Casasnovas <quentin.casasnovas@...cle.com>,
	Steffen Persvold <sp@...ascale.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] x86: Unbreak early processor microcode loading

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@...ascale.com>
> ---
>  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.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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