linux-kernel - Re: [PATCH] x86, kdump, ioapic: Fix kdump race with migrating irq

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]

Date:	Thu, 2 Feb 2012 10:33:20 -0500
From:	Don Zickus <dzickus@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
	vgoyal@...hat.com, kexec-list <kexec@...ts.infradead.org>
Subject: Re: [PATCH] x86, kdump, ioapic: Fix kdump race with migrating irq

On Wed, Feb 01, 2012 at 05:34:01PM -0800, Eric W. Biederman wrote:
> > Talking to folks here and trying to read the code it seems like the PIT
> > stuff is delayed until after the IOAPIC is configured using Fast TSC
> > calibration as a mechanism to work around the PIT??
> >
> > I attached the output of the Pentium4 when kdumping.  Not sure what to
> > really look for to verify the PIC is being skipped.  Perhaps you know?
> 
> The important part is the kexec on panic works without shutting down
> the ioapic.  There should be no corner case issues it should either
> work it should fail.
> 
> The problem used to be that we always would initialize the PIT interrupt
> in the 8259 interrupt controller before we would initialize the ioapics
> and that would kill the boot.
> 
> If I have read your testing correctly you are apparently booting in the
> kexec on panic case.  That seems to be successful to me.  So we should
> be able to just remove the ioapic shutdown code from
> machine_crash_shutdown as it is no longer needed.
> 
> Thank you for being careful and testing on a number of different
> platforms. 

No problem.  I was actually trying to find machines that did not have
ioapics to make sure they still worked (it's hard!).

So if I test on a couple more machines (hopefully one without an ioapic),
can I get your ack?  Or is there something else you would like me to do to
verify things are working correctly?

I will also need your help writing the changelog such that people
understand why removing that line is safe now.

> 
> The only case I can think that won't work without ioapic disables
> is using a crash kernel that doesn't emable the ioapics.

Ok.  I can see that.  Would you agree that scenario is not a very sane
case? :-) Does not using the ioapic really save you anything?

Otherwise the alternative is to use my original patch.

Thanks for the help.

Cheers,
Don

> 
> Eric
--
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/