linux-kernel - Re: [PATCH 7/7] x86/microcode: Recheck IBRS features on microcode reload

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Date:   Fri, 5 Jan 2018 14:32:17 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] x86/microcode: Recheck IBRS features on microcode
 reload

On Thu, Jan 04, 2018 at 07:50:33PM +0100, Borislav Petkov wrote:
> On Thu, Jan 04, 2018 at 07:34:30PM +0100, Andrea Arcangeli wrote:
> > void spec_ctrl_rescan_cpuid(void)
> > {
> > 	int cpu;
> > 
> > 	if (use_ibp_disable)
> > 		return;
> > 	mutex_lock(&spec_ctrl_mutex);
> > 	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL ||
> > 	    boot_cpu_data.x86_vendor == X86_VENDOR_AMD) {
> > 		/* detect spec ctrl related cpuid additions */
> > 		init_scattered_cpuid_features(&boot_cpu_data);
> 
> You don't need to noodle through all the scattered features - just the
> two bits.

Does it really matter?  Rescanning everything can't hurt here, and it
shouldn't be noticable in any boot time chart.  I feel like arguing
about tiny stuff like this takes away from the obvious other problems
this whole patch series had :(

But hey, I'm guilty of it numerous times as well, I know, so I'll shut
up now...

thanks,

greg k-h