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
| ||
|
Date: Tue, 25 Apr 2017 09:31:40 +0000 From: "Lofstedt, Marta" <marta.lofstedt@...el.com> To: Peter Zijlstra <peterz@...radead.org>, "tglx@...utronix.de" <tglx@...utronix.de>, "mingo@...nel.org" <mingo@...nel.org> CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "ville.syrjala@...ux.intel.com" <ville.syrjala@...ux.intel.com>, "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>, "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>, "martin.peres@...ux.intel.com" <martin.peres@...ux.intel.com>, "pasha.tatashin@...cle.com" <pasha.tatashin@...cle.com>, "daniel.vetter@...ll.ch" <daniel.vetter@...ll.ch> Subject: RE: [PATCH 0/9] sched_clock fixes Hi Peterz, I tested your patch-set on the same Core2 machine as where we discovered the regression. With the tsc=unstable boot param that passrate has improved significantly; 350 fails -> 15 fails. BR, Marta > -----Original Message----- > From: Peter Zijlstra [mailto:peterz@...radead.org] > Sent: Friday, April 21, 2017 5:58 PM > To: tglx@...utronix.de; mingo@...nel.org > Cc: linux-kernel@...r.kernel.org; ville.syrjala@...ux.intel.com; > daniel.lezcano@...aro.org; Wysocki, Rafael J <rafael.j.wysocki@...el.com>; > Lofstedt, Marta <marta.lofstedt@...el.com>; martin.peres@...ux.intel.com; > pasha.tatashin@...cle.com; peterz@...radead.org; daniel.vetter@...ll.ch > Subject: [PATCH 0/9] sched_clock fixes > > Hi, > > These patches were inspired (and hopefully fix) two independent bug > reports on > Core2 machines. > > I never could quite reproduce one, but my Core2 machine no longer switches > to stable sched_clock and therefore no longer tickles the problematic stable - > > unstable transition either. > > Before I dug up my Core2 machine, I tried emulating TSC wreckage by poking > random values into the TSC MSR from userspace. Behaviour in that case is > improved as well. > > People have to realize that if we manage to boot with TSC 'stable' (both > sched_clock and clocksource) and we later find out we were mistaken (we > observe a TSC wobble) the clocks that are derived from it _will_ have had an > observable hickup. This is fundamentally unfixable. > > If you own a machine where the BIOS tries to hide SMI latencies by > rewinding TSC (yes, this is a thing), the very best we can do is mark TSC > unstable with a boot parameter. > > For example, this is me writing a stupid value into the TSC: > > [ 46.745082] random: crng init done > [18443029775.010069] clocksource: timekeeping watchdog on CPU0: Marking > clocksource 'tsc' as unstable because the skew is too large: > [18443029775.023141] clocksource: 'hpet' wd_now: 3ebec538 > wd_last: 3e486ec9 mask: ffffffff > [18443029775.034214] clocksource: 'tsc' cs_now: 5025acce9 cs_last: > 24dc3bd21c88ee mask: ffffffffffffffff > [18443029775.046651] tsc: Marking TSC unstable due to clocksource > watchdog [18443029775.054211] TSC found unstable after boot, most likely > due to broken BIOS. Use 'tsc=unstable'. > [18443029775.064434] sched_clock: Marking unstable (70569005835, - > 17833788)<-(-3714295689546517, -2965802361) > [ 70.573700] clocksource: Switched to clocksource hpet > > With some trace_printk()s (not included) I could tell that the wobble occured > at 69.965474. The clock now resumes where it 'should' have been. > > But an unfortunate scheduling event could have resulted in one task having > seen a runtime of ~584 years with 'obvious' effects. Similar jumps can also be > observed from userspace GTOD usage. >
Powered by blists - more mailing lists