linux-kernel - Re: [PATCH] kdump: force page alignment for per-CPU crash notes.

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Message-ID: <20120301183115.GE13533@redhat.com>
Date:	Thu, 1 Mar 2012 13:31:15 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Eugene Surovegin <surovegin@...gle.com>
Cc:	linux-kernel@...r.kernel.org,
	Eric Biederman <ebiederm@...ssion.com>,
	kexec-list <kexec@...ts.infradead.org>
Subject: Re: [PATCH] kdump: force page alignment for per-CPU crash notes.

On Thu, Mar 01, 2012 at 09:04:32AM -0800, Eugene Surovegin wrote:
> On Thu, Mar 1, 2012 at 7:09 AM, Vivek Goyal <vgoyal@...hat.com> wrote:
> > On Wed, Feb 29, 2012 at 09:21:23AM -0800, Eugene Surovegin wrote:
> >> Per-CPU allocations are not guaranteed to be physically contiguous.
> >> However, kdump kernel and user-space code assumes that per-CPU
> >> memory, used for saving CPU registers on crash, is.
> >> This can cause corrupted /proc/vmcore in some cases - the main
> >> symptom being huge ELF note section.
> >>
> >> Force page alignment for note_buf_t to ensure that this assumption holds.
> >>
> >
> > Hi Eugene,
> >
> > Where do we make assumption that crash_notes address is page aligned?
> 
> I never said that. I said that assumption was that note chunks were
> physically contiguous.
> 
> [snip]
> 
> > Are you referring to the fact that note could be stored on two different
> > physical pages and then kexec-tools does not know about the physical
> > address of second page, hence second kernel does not know about it
> > and we never read that data. That sounds like a problem.
> 
> Yes. This is exactly what happens in some cases.

Ok. Thanks for clarifying. Patch looks good to me.

Acked-by: Vivek Goyal <vgoyal@...hat.com>

Vivek
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