From: Miroslav Benes <mbenes@suse.cz>
To: Chris J Arges <chris.j.arges@canonical.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
Jiri Kosina <jikos@kernel.org>,
jeyu@redhat.com, eugene.shatokhin@rosalab.ru,
live-patching@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
pmladek@suse.cz
Subject: Re: Bug with paravirt ops and livepatches
Date: Wed, 6 Apr 2016 16:17:37 +0200 (CEST) [thread overview]
Message-ID: <alpine.LNX.2.00.1604061615550.30748@pobox.suse.cz> (raw)
In-Reply-To: <20160406134833.GA12961@canonical.com>
On Wed, 6 Apr 2016, Chris J Arges wrote:
> On Wed, Apr 06, 2016 at 02:09:01PM +0200, Miroslav Benes wrote:
> > On Wed, 6 Apr 2016, Chris J Arges wrote:
> >
> > > I think this approach needs more thought and my code has bug(s).
> >
> > And indeed there is...
> >
> > long (*__kvm_arch_vm_ioctl)(struct file *filp, unsigned long ioctl, unsigned long arg) = NULL;
> >
> > Use a different name than __kvm_arch_vm_ioctl and (ideally) make it
> > static.
> >
> > kallsyms_lookup_name("__kvm_arch_vm_ioctl") returns the address of this
> > variable from the patch module.
> >
> > Miroslav
> >
>
> Well that was the bug, I was really stumped why it was giving me a wierd
> address for a function. Once I changed my pointer name to something else it
> worked, so there was no difference to these approaches. I also had to modify
> the symbol lookup to happen in the livepatch so we ensure that the module is
> loaded in this case and not get a NULL deref.
Just a remark. With this change there is a call to kallsyms_lookup_name
for each call to patched function. This is not optimal. What we do in
kgraft is that we register a module notifier which calls
kallsyms_lookup_name when to-be-patched module arrives. It is not nice but
it works.
Miroslav
>
> The fixed code is here:
> http://people.canonical.com/~arges/livepatch_issue/livepatch_kvm_arch_vm_ioctl.works.2/
>
> This out of tree patch doesn't have the same failure as building a patch with
> kpatch-build which is what we expect since it doesn't have livepatch relocs. In
> addition I tested with the kvm module loaded _after_ the livepatch module and
> no failure was observed.
>
> --chris
>
prev parent reply other threads:[~2016-04-06 14:17 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-29 12:05 Bug with paravirt ops and livepatches Chris J Arges
2016-03-29 13:01 ` Miroslav Benes
2016-03-29 13:05 ` Jiri Kosina
2016-04-01 15:01 ` Jiri Kosina
2016-04-01 15:46 ` Miroslav Benes
2016-04-01 16:01 ` Chris J Arges
2016-04-01 19:07 ` Chris J Arges
2016-04-01 19:35 ` Jiri Kosina
2016-04-04 16:14 ` Josh Poimboeuf
2016-04-04 17:58 ` Jessica Yu
2016-04-05 13:07 ` Miroslav Benes
2016-04-05 13:53 ` Evgenii Shatokhin
2016-04-05 14:24 ` Josh Poimboeuf
2016-04-05 19:19 ` Jessica Yu
2016-04-06 8:30 ` Miroslav Benes
2016-04-06 8:43 ` Miroslav Benes
2016-04-06 9:09 ` Miroslav Benes
2016-04-06 17:23 ` Jessica Yu
2016-04-06 16:55 ` Jessica Yu
2016-04-05 23:27 ` Chris J Arges
2016-04-06 9:09 ` Miroslav Benes
2016-04-06 10:38 ` Chris J Arges
2016-04-06 12:09 ` Miroslav Benes
2016-04-06 13:48 ` Chris J Arges
2016-04-06 14:17 ` Miroslav Benes [this message]
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