linux-kernel - Re: [PATCH] x86/apic: Handle missing global clockevent gracefully

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.21.1908092138520.21433@nanos.tec.linutronix.de>
Date:   Fri, 9 Aug 2019 21:40:26 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Lendacky, Thomas" <Thomas.Lendacky@....com>
cc:     "Li, Aubrey" <aubrey.li@...ux.intel.com>,
        Daniel Drake <drake@...lessm.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Endless Linux Upstreaming Team <linux@...lessm.com>,
        Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH] x86/apic: Handle missing global clockevent gracefully

On Fri, 9 Aug 2019, Lendacky, Thomas wrote:
> On 8/9/19 7:54 AM, Thomas Gleixner wrote:
> > +	local_irq_disable();
> >   	/*
> >   	 * Setup the APIC counter to maximum. There is no way the lapic
> >   	 * can underflow in the 100ms detection time frame
> >   	 */
> >   	__setup_APIC_LVTT(0xffffffff, 0, 0);
> >   
> > -	/* Let the interrupts run */
> > -	local_irq_enable();
> > +	/*
> > +	 * Methods to terminate the calibration loop:
> > +	 *  1) Global clockevent if available (jiffies)
> > +	 *  2) TSC if available and frequency is known
> > +	 */
> > +	jif_start = READ_ONCE(jiffies);
> > +
> > +	if (tsc_khz) {
> > +		tsc_start = rdtsc();
> > +		tsc_perj = div_u64((u64)tsc_khz * 1000, HZ);
> > +	}
> > +
> > +	while (lapic_cal_loops <= LAPIC_CAL_LOOPS) {
> > +		/*
> > +		 * Enable interrupts so the tick can fire, if a global
> > +		 * clockevent device is available
> > +		 */
> > +		local_irq_enable();
> 
> Just a nit, but you end up doing this at the bottom of the loop, so you
> could move this invocation to just before the loop and avoid doing two
> local_irq_enable() calls in succession after the first iteration.

Indeed. Lets see how the reports go. That change is a nobrainer.

Thanks,

	tglx