Re: [PATCH RESEND] CPU hotplug,x86 Microcode: Don't request microcode from userspace unnecessarily

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Sunday, October 09, 2011, Srivatsa S. Bhat wrote:
> Requesting the microcode from userspace *every time* when onlining CPUs
> (during a CPU hotplug operation) is unnecessary.
> 
> So, this patch ensures that once the kernel gets the microcode after booting,
> it is not freed nor invalidated when a CPU goes offline, so that it can be
> reused when that CPU comes back online, without requesting userspace for it
> again. As a result, the CPU hotplug operations become faster as well.
> 
> Tested-by: Borislav Petkov <bp@amd64.org>
> Acked-by: Borislav Petkov <bp@amd64.org>
> 
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>

Fine by me.  I wonder who should take this?

Rafael


> ---
> 
>  arch/x86/kernel/microcode_core.c |    9 ++++++++-
>  1 files changed, 8 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kernel/microcode_core.c b/arch/x86/kernel/microcode_core.c
> index f924280..33c8a67 100644
> --- a/arch/x86/kernel/microcode_core.c
> +++ b/arch/x86/kernel/microcode_core.c
> @@ -483,7 +483,14 @@ mc_cpu_callback(struct notifier_block *nb, unsigned long action, void *hcpu)
>  		sysfs_remove_group(&sys_dev->kobj, &mc_attr_group);
>  		pr_debug("CPU%d removed\n", cpu);
>  		break;
> -	case CPU_DEAD:
> +
> +	/*
> +	 * When a CPU goes offline, don't free up or invalidate the copy of
> +	 * the microcode in kernel memory, so that we can reuse it when the
> +	 * CPU comes back online without unnecessarily requesting the userspace
> +	 * for it again.
> +	 */
> +
>  	case CPU_UP_CANCELED_FROZEN:
>  		/* The CPU refused to come up during a system resume */
>  		microcode_fini_cpu(cpu);
> 
> 
> 
>