Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image

From: Bhupesh SHARMA <bhupesh.linux@gmail.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Russell King - ARM Linux admin <linux@armlinux.org.uk>,
	Baoquan He <bhe@redhat.com>,
	 David Hildenbrand <david@redhat.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	 Bhupesh Sharma <bhsharma@redhat.com>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	 kexec@lists.infradead.org, linux-mm@kvack.org,
	 James Morse <james.morse@arm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	 Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image
Date: Mon, 13 Apr 2020 02:07:58 +0530	[thread overview]
Message-ID: <CAFTCetT=7rYm_yPSZWjT=+fKPujuqwKyY_2aBcAR17AifuHaoA@mail.gmail.com> (raw)
In-Reply-To: <87wo6klbw0.fsf@x220.int.ebiederm.org>

On Mon, Apr 13, 2020 at 1:26 AM Eric W. Biederman <ebiederm@xmission.com> wrote:
>
>
> The only benefit of kexec_file_load is that it is simple enough from a
> kernel perspective that signatures can be checked.
>
> kexec_load in every other respect is the more capable and functional
> interface.  It makes no sense to get rid of it.
>
> It does make sense to reload with a loaded kernel on memory hotplug.
> That is simple and easy.  If we are going to handle something in the
> kernel it should simple an automated unloading of the kernel on memory
> hotplug.
>
>
> I think it would be irresponsible to deprecate kexec_load on any
> platform.
>
> I also suspect that kexec_file_load could be taught to copy the dtb
> on arm32 if someone wants to deal with signatures.
>
> We definitely can not even think of deprecating kexec_load until
> architecture that supports it also supports kexec_file_load and everyone
> is happy with that interface.  That is Linus's no regression rule.

TBH, I have seen several active users of kexec_load on arm32
environments and we have been trying to help them with kexec issues on
arm32 in recent past as well.

So, I agree with Eric's view that probably deprecating this in favour
of kexec_file_load will break these existing environment.

I tried to do some work at the start of this year to add
kexec_file_load support for arm32 in my spare cycles, but I gave up as
the arm32 hardware had a broken firmware and couldn't boot latest
upstream kernel.

May be I try to find some spare cycles in the coming days to do it.

But I think since kexec_load is an important interface on these arm32
boards for supporting existing kexec-based bootloaders, we should
continue supporting the same until kexec_file_load is supported/mature
enough for arm32.

Thanks,
Bhupesh