linux-kernel - Re: [PATCH v3 1/3] kexec: Move vmcoreinfo out of the kernel's .bss section

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Date:   Wed, 22 Mar 2017 12:30:04 +0800
From:   Dave Young <dyoung@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Baoquan He <bhe@...hat.com>, Xunlei Pang <xlpang@...hat.com>,
        Atsushi Kumagai <ats-kumagai@...jp.nec.com>,
        Petr Tesarik <ptesarik@...e.cz>, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, kexec@...ts.infradead.org,
        holzheu@...ux.vnet.ibm.com, mahesh@...ux.vnet.ibm.com,
        hbathini@...ux.vnet.ibm.com
Subject: Re: [PATCH v3 1/3] kexec: Move vmcoreinfo out of the kernel's .bss
 section

On 03/21/17 at 10:18pm, Eric W. Biederman wrote:
> Dave Young <dyoung@...hat.com> writes:
> 
> > On 03/20/17 at 10:33pm, Eric W. Biederman wrote:
> >> Xunlei Pang <xlpang@...hat.com> writes:
> >> 
> >> > As Eric said,
> >> > "what we need to do is move the variable vmcoreinfo_note out
> >> > of the kernel's .bss section.  And modify the code to regenerate
> >> > and keep this information in something like the control page.
> >> >
> >> > Definitely something like this needs a page all to itself, and ideally
> >> > far away from any other kernel data structures.  I clearly was not
> >> > watching closely the data someone decided to keep this silly thing
> >> > in the kernel's .bss section."
> >> >
> >> > This patch allocates extra pages for these vmcoreinfo_XXX variables,
> >> > one advantage is that it enhances some safety of vmcoreinfo, because
> >> > vmcoreinfo now is kept far away from other kernel data structures.
> >> 
> >> Can you preceed this patch with a patch that removes CRASHTIME from
> >> vmcoreinfo?  If someone actually cares we can add a separate note that holds
> >> a 64bit crashtime in the per cpu notes.  
> >
> > I think makedumpfile is using it, but I also vote to remove the
> > CRASHTIME. It is better not to do this while crashing and a makedumpfile
> > userspace patch is needed to drop the use of it.
> >
> >> 
> >> As we are looking at reliability concerns removing CRASHTIME should make
> >> everything in vmcoreinfo a boot time constant.  Which should simplify
> >> everything considerably.
> >
> > It is a nice improvement..
> 
> We also need to take a close look at what s390 is doing with vmcoreinfo.
> As apparently it is reading it in a different kind of crashdump process.

Yes, need careful review from s390 and maybe ppc64 especially about
patch 2/3, better to have comments from IBM about s390 dump tool and ppc
fadump. Added more cc.

Thanks
Dave