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Mike Rapoport bde9cfa3af x86/setup: don't remove E820_TYPE_RAM for pfn 0 
Patch series "mm: fix initialization of struct page for holes in  memory layout", v3.

Commit 73a6e474cb ("mm: memmap_init: iterate over memblock regions
rather that check each PFN") exposed several issues with the memory map
initialization and these patches fix those issues.

Initially there were crashes during compaction that Qian Cai reported
back in April [1].  It seemed back then that the problem was fixed, but
a few weeks ago Andrea Arcangeli hit the same bug [2] and there was an
additional discussion at [3].

[1] https://lore.kernel.org/lkml/8C537EB7-85EE-4DCF-943E-3CC0ED0DF56D@lca.pw
[2] https://lore.kernel.org/lkml/20201121194506.13464-1-aarcange@redhat.com
[3] https://lore.kernel.org/mm-commits/20201206005401.qKuAVgOXr%akpm@linux-foundation.org

This patch (of 2):

The first 4Kb of memory is a BIOS owned area and to avoid its allocation
for the kernel it was not listed in e820 tables as memory.  As the result,
pfn 0 was never recognised by the generic memory management and it is not
a part of neither node 0 nor ZONE_DMA.

If set_pfnblock_flags_mask() would be ever called for the pageblock
corresponding to the first 2Mbytes of memory, having pfn 0 outside of
ZONE_DMA would trigger

	VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);

Along with reserving the first 4Kb in e820 tables, several first pages are
reserved with memblock in several places during setup_arch().  These
reservations are enough to ensure the kernel does not touch the BIOS area
and it is not necessary to remove E820_TYPE_RAM for pfn 0.

Remove the update of e820 table that changes the type of pfn 0 and move
the comment describing why it was done to trim_low_memory_range() that
reserves the beginning of the memory.

Link: https://lkml.kernel.org/r/20210111194017.22696-2-rppt@kernel.org
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Qian Cai <cai@lca.pw>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-01-24 09:20:52 -08:00
arch x86/setup: don't remove E820_TYPE_RAM for pfn 0 2021-01-24 09:20:52 -08:00
block block-5.11-2021-01-10 2021-01-10 12:53:08 -08:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto X.509: Fix crash caused by NULL pointer 2021-01-20 11:33:51 -08:00
Documentation SCSI fixes on 20210122 2021-01-23 11:35:02 -08:00
drivers Merge branch 'mtd/fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux 2021-01-23 12:02:58 -08:00
fs A patch to zero out sensitive cryptographic data and two minor cleanups 2021-01-22 13:47:25 -08:00
include Networking fixes for 5.11-rc5, including fixes from bpf, wireless, 2021-01-20 11:52:21 -08:00
init Revert "init/console: Use ttynull as a fallback when there is no console" 2021-01-08 11:02:18 -08:00
ipc Merge branch 'akpm' (patches from Andrew) 2020-12-15 12:53:37 -08:00
kernel Printk fixes for 5.11-rc5 2021-01-21 11:37:22 -08:00
lib Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2021-01-17 12:16:47 -08:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
mm mm/memblock: Fix typo in comment of memblock_phys_alloc_try_nid() 2021-01-21 10:29:37 +02:00
net A patch to zero out sensitive cryptographic data and two minor cleanups 2021-01-22 13:47:25 -08:00
samples ARM: SoC drivers for v5.11 2020-12-16 16:38:41 -08:00
scripts Kbuild fixes for v5.11 2021-01-10 13:24:55 -08:00
security dump_common_audit_data(): fix racy accesses to ->d_name 2021-01-16 15:11:35 -05:00
sound ALSA: usb-audio: Fix hw constraints dependencies 2021-01-20 21:46:45 +01:00
tools linux-kselftest-kunit-fixes-5.11-rc5 2021-01-23 11:25:33 -08:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt x86: 2021-01-08 15:06:02 -08:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: docs: ignore sphinx_*/ directories 2020-09-10 10:44:31 -06:00
.mailmap MAINTAINERS: Update my email address 2021-01-15 23:55:16 +01:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: dccp: move Gerrit Renker to CREDITS 2021-01-14 10:53:49 -08:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS sound fixes for 5.11-rc5 2021-01-21 11:25:35 -08:00
Makefile Linux 5.11-rc4 2021-01-17 16:37:05 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.