linux-kernel - Re: [PATCH] arch: x86: init hpet event

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 for Android: free password hash cracker in your pocket

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

Message-ID: <alpine.LFD.2.02.1205072150590.6271@ionos>
Date:	Mon, 7 May 2012 22:26:34 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Vladimir Davydov <vdavydov@...allels.com>
cc:	"Venkatesh Pallipadi (Venki)" <venki@...gle.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arch: x86: init hpet event_handler to noop

On Tue, 24 Apr 2012, Vladimir Davydov wrote:

> If hpet is enabled by hpet_late_init() - this usually occurs on systems
> with buggy BIOS, which does not report about hpet presence through ACPI,
> hpet_clockevent's event_handler can be left uninitialized by
> clockevents_register_device() because of hpet_clockevent low rating (by
> the time hpet_late_init() is called, high prio apic timers have already
> been setup). The event_handler is then initialized a bit later by the
> clocksource_done_booting() procedure.
> 

This explanation is worse than an oracle and aside of that, it's
patently wrong.

How the hell is clocksource_done_booting() related to the HPET
clockevent mechanism?

> Normally, timer interrupts should not be delivered between these two
> calls, but if e.g. the kernel is booted using kexec, there might be some
> pending interrupts from the previous kernel's context, which can lead to
> a NULL pointer dereference in timer_interrupt().

How is kexec related to this?

And how should pending interrupts be not handled by the always first
initialized PIT ?

> Avoid this by initializing hpet's event_handler to noop in its definition.

"Avoid" is the correct term: You're avoiding to track down the root
cause of the problem. 

This is fairy tale mode. I really love fairy tales, just not in the
context of kernel code.

Please provide proper proof why this can happen instead of some
handwavy explanations.

Thanks,

	tglx
--
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/