linux-kernel - Re: [PATCH] lguest-fix-divide-error-implement-sched

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: <4665AEE5.7040904@zytor.com>
Date:	Tue, 05 Jun 2007 11:43:49 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <ak@...e.de>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Matt Mackall <mpm@...enic.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lguest-fix-divide-error-implement-sched_clock

Andi Kleen wrote:
> 
> I don't think it's a good idea for the TSC. There are various
> setups where it is unreliable and also often simulators don't 
> implement it correctly. And it's always a valuable workaround
> to be able to turn it off.
> 

I dug some more into the TSC code, and found some other annoying stuff:

/*
 * Make an educated guess if the TSC is trustworthy and synchronized
 * over all CPUs.
 */
__cpuinit int unsynchronized_tsc(void)
{
        if (!cpu_has_tsc || tsc_unstable)
                return 1;
        /*
         * Intel systems are normally all synchronized.
         * Exceptions must mark TSC as unstable:
         */
        if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
                /* assume multi socket systems are not synchronized: */
                if (num_possible_cpus() > 1)
                        tsc_unstable = 1;
        }
        return tsc_unstable;
}

That's a vendor check foul.  That should be a CPU feature flag.

Looks like there is some work to be done here.

	-hpa
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/