[RFC 0/3] kdump: Check mem_map of CMA area in kdump

From: Pingfan Liu <kernelfans@gmail.com>
To: kexec@lists.infradead.org
Cc: Pingfan Liu <piliu@redhat.com>, Jiri Bohac <jbohac@suse.cz>,
	Michal Hocko <mhocko@suse.com>, Philipp Rudo <prudo@redhat.com>,
	Baoquan He <bhe@redhat.com>, Dave Young <dyoung@redhat.com>
Subject: [RFC 0/3] kdump: Check mem_map of CMA area in kdump
Date: Mon, 18 Dec 2023 13:23:22 +0800	[thread overview]
Message-ID: <20231218052325.20982-1-kernelfans@gmail.com> (raw)

From: Pingfan Liu <piliu@redhat.com>

First of all, this series is only for proof of concept. It only passes compilation.

For years, CMA is proposed to be used as crashkernel reserved memory.
But DIO prevent us to follow it since DMA may be in-flight and ruin the
kdump kernel.

This series exports the crash kernel's CMA area information through
device-tree, and kdump kernel skips any page, which refcnt!=mapcount and
has a potential DMA activity.

The exported information include:
	u64 kdump_cma_pfn;
	u64 kdump_cma_pg_cnt;
	u64 kdump_cma_pg_paddr;

And they should be filled with Jiri's series "[PATCH 0/4] kdump:
crashkernel reservation from CMA"

After the conjunction of two series, the CMA used for kdump has only the
following risk, where the following conditions:
	-1.a wrong code forges _refcnt and mapcount to the same value
	-2.the page is also used by DIO

Is it acceptable, or any rescue e.g. CRC on page?

Please share your thoughts.

Thanks,

Pingfan

Cc: Jiri Bohac <jbohac@suse.cz>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Philipp Rudo <prudo@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
To: kexec@lists.infradead.org
---
Pingfan Liu (3):
  crash_dump: Parse the CMA's mem_map in kdump
  of: kexec: Set up properties for reusing CMA in kdump
  of: fdt: Parse properties of reusing CMA in kdump

 drivers/of/fdt.c      | 43 +++++++++++++++++++++++
 drivers/of/kexec.c    | 14 ++++++++
 include/linux/kexec.h |  5 +++
 init/main.c           |  4 +++
 kernel/crash_dump.c   | 80 +++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 146 insertions(+)

-- 
2.31.1

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