linux-kernel - Re: [PATCH] x86/microcode/intel: Check microcode revision before updating sibling threads

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Date:   Sat, 17 Feb 2018 08:50:53 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Ashok Raj <ashok.raj@...el.com>
Cc:     bp@...e.de, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86/microcode/intel: Check microcode revision before
 updating sibling threads


* Ashok Raj <ashok.raj@...el.com> wrote:

> After updating microcode on one of the threads in the core, the
> thread sibling automatically gets the update since the microcode
> resources are shared. Check the ucode revision on the cpu before
> performing a ucode update.

s/cpu/CPU

> 
> Signed-off-by: Ashok Raj <ashok.raj@...el.com>
> Cc: X86 ML <x86@...nel.org>
> Cc: LKML <linux-kernel@...r.kernel.org>
> ---
>  arch/x86/kernel/cpu/microcode/intel.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
> index 09b95a7..036d1db 100644
> --- a/arch/x86/kernel/cpu/microcode/intel.c
> +++ b/arch/x86/kernel/cpu/microcode/intel.c
> @@ -776,7 +776,7 @@ static enum ucode_state apply_microcode_intel(int cpu)
>  {
>  	struct microcode_intel *mc;
>  	struct ucode_cpu_info *uci;
> -	struct cpuinfo_x86 *c;
> +	struct cpuinfo_x86 *c = &cpu_data(cpu);
>  	static int prev_rev;
>  	u32 rev;
>  
> @@ -793,6 +793,18 @@ static enum ucode_state apply_microcode_intel(int cpu)
>  			return UCODE_NFOUND;
>  	}
>  
> +	rev = intel_get_microcode_revision();
> +	/*
> +	 * Its possible the microcode got udpated
> +	 * because its sibling update was done earlier.
> +	 * Skip the udpate in that case.
> +	 */
> +	if (rev >= mc->hdr.rev) {
> +		uci->cpu_sig.rev = rev;
> +		c->microcode = rev;
> +		return UCODE_OK;
> +	}

s/udpate
 /update

Also, more fundamentally, during microcode early testing, isn't it possible for 
internal iterations of the microcode to have the same revision, but be different?

This patch would prevent re-loading it - for a seemingly minimal benefit.

Thanks,

	Ingo