linux-kernel - Re: [PATCH] kexec: unmap reserved pages for each error-return way

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Date:	Thu, 28 Jan 2016 11:32:17 +0100
From:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Dmitry Safonov <dsafonov@...tuozzo.com>,
	<linux-kernel@...r.kernel.org>, <schwidefsky@...ibm.com>,
	<heiko.carstens@...ibm.com>, <ebiederm@...ssion.com>,
	<kexec@...ts.infradead.org>, <linux-s390@...r.kernel.org>,
	<dyoung@...hat.com>, <0x7f454c46@...il.com>,
	Xunlei Pang <xlpang@...hat.com>
Subject: Re: [PATCH] kexec: unmap reserved pages for each error-return way

On Wed, 27 Jan 2016 11:15:46 -0800
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Wed, 27 Jan 2016 14:48:31 +0300 Dmitry Safonov <dsafonov@...tuozzo.com> wrote:
> 
> > For allocation of kimage failure or kexec_prepare or load segments
> > errors there is no need to keep crashkernel memory mapped.
> > It will affect only s390 as map/unmap hook defined only for it.
> > As on unmap s390 also changes os_info structure let's check return code
> > and add info only on success.
> > 
> 
> This conflicts (both mechanically and somewhat conceptually) with
> Xunlei Pang's "kexec: Introduce a protection mechanism for the
> crashkernel reserved memory" and "kexec: provide
> arch_kexec_protect(unprotect)_crashkres()".
> 
> http://ozlabs.org/~akpm/mmots/broken-out/kexec-introduce-a-protection-mechanism-for-the-crashkernel-reserved-memory.patch
> http://ozlabs.org/~akpm/mmots/broken-out/kexec-introduce-a-protection-mechanism-for-the-crashkernel-reserved-memory-v4.patch
> 
> and
> 
> http://ozlabs.org/~akpm/mmots/broken-out/kexec-provide-arch_kexec_protectunprotect_crashkres.patch
> http://ozlabs.org/~akpm/mmots/broken-out/kexec-provide-arch_kexec_protectunprotect_crashkres-v4.patch

Hmm, It looks to me that arch_kexec_(un)protect_crashkres() has exactly
the same semantics as crash_(un)map_reserved_pages().

On s390 we don't have the crashkernel memory mapped and therefore need
crash_map_reserved_pages() before loading something into crashkernel
memory.

Perhaps I missed something?
Michael