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83b2d345e1
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Mike Rapoport (Microsoft) 83b2d345e1 x86/e820: Discard high memory that can't be addressed by 32-bit systems 
Dave Hansen reports the following crash on a 32-bit system with
CONFIG_HIGHMEM=y and CONFIG_X86_PAE=y:

  > 0xf75fe000 is the mem_map[] entry for the first page >4GB. It
  > obviously wasn't allocated, thus the oops.

  BUG: unable to handle page fault for address: f75fe000
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  *pdpt = 0000000002da2001 *pde = 000000000300c067 *pte = 0000000000000000
  Oops: Oops: 0002 [#1] SMP NOPTI
  CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.15.0-rc1-00288-ge618ee89561b-dirty #311 PREEMPT(undef)
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
  EIP: __free_pages_core+0x3c/0x74
  ...
  Call Trace:
   memblock_free_pages+0x11/0x2c
   memblock_free_all+0x2ce/0x3a0
   mm_core_init+0xf5/0x320
   start_kernel+0x296/0x79c
   i386_start_kernel+0xad/0xb0
   startup_32_smp+0x151/0x154

The mem_map[] is allocated up to the end of ZONE_HIGHMEM which is defined
by max_pfn.

The bug was introduced by this recent commit:

  6faea3422e ("arch, mm: streamline HIGHMEM freeing")

Previously, freeing of high memory was also clamped to the end of
ZONE_HIGHMEM but after this change, memblock_free_all() tries to
free memory above the of ZONE_HIGHMEM as well and that causes
access to mem_map[] entries beyond the end of the memory map.

To fix this, discard the memory after max_pfn from memblock on
32-bit systems so that core MM would be aware only of actually
usable memory.

Fixes: 6faea3422e ("arch, mm: streamline HIGHMEM freeing")
Reported-by: Dave Hansen <dave.hansen@intel.com>
Tested-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Shevchenko <andy@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Davide Ciminaghi <ciminaghi@gnudd.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: kvm@vger.kernel.org
Link: https://lore.kernel.org/r/20250413080858.743221-1-rppt@kernel.org # discussion and submission
2025-04-19 16:48:18 +02:00
arch x86/e820: Discard high memory that can't be addressed by 32-bit systems 2025-04-19 16:48:18 +02:00
block block-6.15-20250417 2025-04-18 09:21:14 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: ahash - Disable request chaining 2025-04-12 09:33:09 +08:00
Documentation Power management fixes for 6.15-rc3 2025-04-18 13:06:12 -07:00
drivers Miscellaneous fixes: 2025-04-18 13:28:41 -07:00
fs smb client fixes 2025-04-18 20:10:42 -07:00
include Miscellaneous fixes: 2025-04-18 13:28:41 -07:00
init Miscellaneous scheduler fixes/updates: 2025-04-06 10:44:58 -07:00
io_uring io_uring/zcrx: fix late dma unmap for a dead dev 2025-04-18 06:12:10 -06:00
ipc treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
kernel cpufreq/sched: Set need_freq_update in ignore_dl_rate_limit() 2025-04-17 17:54:44 +02:00
lib hardening fixes for v6.15-rc3 2025-04-18 13:20:20 -07:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm hardening fixes for v6.15-rc3 2025-04-18 13:20:20 -07:00
net Including fixes from Bluetooth, CAN and Netfilter. 2025-04-17 11:45:30 -07:00
rust Kbuild updates for v6.15 2025-04-05 15:46:50 -07:00
samples samples/livepatch: add module descriptions 2025-04-11 17:32:38 -07:00
scripts genksyms: Handle typeof_unqual keyword and __seg_{fs,gs} qualifiers 2025-04-14 09:19:04 +02:00
security hardening: Disable GCC randstruct for COMPILE_TEST 2025-04-15 13:50:17 -07:00
sound ASoC: Fixes for v6.15 2025-04-11 15:51:19 +02:00
tools hardening fixes for v6.15-rc3 2025-04-18 13:20:20 -07:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-05 04:06:45 +09:00
virt ARM: 2025-04-08 13:47:55 -07:00
.clang-format clang-format: Update the ForEachMacros list for v6.15-rc1 2025-04-13 11:03:59 +02:00
.clippy.toml rust: give Clippy the minimum supported Rust version 2025-01-10 00:17:25 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: Create intermediate vmlinux build with relocations preserved 2025-03-17 00:29:50 +09:00
.mailmap sound fixes for 6.15-rc3 2025-04-17 10:14:51 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS Including fixes from netfilter. 2025-04-04 09:15:35 -07:00
Kbuild drm: ensure drm headers are self-contained and pass kernel-doc 2025-02-12 10:44:43 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS Including fixes from Bluetooth, CAN and Netfilter. 2025-04-17 11:45:30 -07:00
Makefile Linux 6.15-rc2 2025-04-13 11:54:49 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -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 reStructuredText 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.