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Shuai Xue 974193e137 mm/hwpoison: do not send SIGBUS to processes with recovered clean pages 
commit aaf99ac2ce upstream.

When an uncorrected memory error is consumed there is a race between the
CMCI from the memory controller reporting an uncorrected error with a UCNA
signature, and the core reporting and SRAR signature machine check when
the data is about to be consumed.

- Background: why *UN*corrected errors tied to *C*MCI in Intel platform [1]

Prior to Icelake memory controllers reported patrol scrub events that
detected a previously unseen uncorrected error in memory by signaling a
broadcast machine check with an SRAO (Software Recoverable Action
Optional) signature in the machine check bank.  This was overkill because
it's not an urgent problem that no core is on the verge of consuming that
bad data.  It's also found that multi SRAO UCE may cause nested MCE
interrupts and finally become an IERR.

Hence, Intel downgrades the machine check bank signature of patrol scrub
from SRAO to UCNA (Uncorrected, No Action required), and signal changed to
#CMCI.  Just to add to the confusion, Linux does take an action (in
uc_decode_notifier()) to try to offline the page despite the UC*NA*
signature name.

- Background: why #CMCI and #MCE race when poison is consuming in Intel platform [1]

Having decided that CMCI/UCNA is the best action for patrol scrub errors,
the memory controller uses it for reads too.  But the memory controller is
executing asynchronously from the core, and can't tell the difference
between a "real" read and a speculative read.  So it will do CMCI/UCNA if
an error is found in any read.

Thus:

1) Core is clever and thinks address A is needed soon, issues a speculative read.
2) Core finds it is going to use address A soon after sending the read request
3) The CMCI from the memory controller is in a race with MCE from the core
   that will soon try to retire the load from address A.

Quite often (because speculation has got better) the CMCI from the memory
controller is delivered before the core is committed to the instruction
reading address A, so the interrupt is taken, and Linux offlines the page
(marking it as poison).

- Why user process is killed for instr case

Commit 046545a661 ("mm/hwpoison: fix error page recovered but reported
"not recovered"") tries to fix noise message "Memory error not recovered"
and skips duplicate SIGBUSs due to the race.  But it also introduced a bug
that kill_accessing_process() return -EHWPOISON for instr case, as result,
kill_me_maybe() send a SIGBUS to user process.

If the CMCI wins that race, the page is marked poisoned when
uc_decode_notifier() calls memory_failure().  For dirty pages,
memory_failure() invokes try_to_unmap() with the TTU_HWPOISON flag,
converting the PTE to a hwpoison entry.  As a result,
kill_accessing_process():

- call walk_page_range() and return 1 regardless of whether
  try_to_unmap() succeeds or fails,
- call kill_proc() to make sure a SIGBUS is sent
- return -EHWPOISON to indicate that SIGBUS is already sent to the
  process and kill_me_maybe() doesn't have to send it again.

However, for clean pages, the TTU_HWPOISON flag is cleared, leaving the
PTE unchanged and not converted to a hwpoison entry.  Conversely, for
clean pages where PTE entries are not marked as hwpoison,
kill_accessing_process() returns -EFAULT, causing kill_me_maybe() to send
a SIGBUS.

Console log looks like this:

    Memory failure: 0x827ca68: corrupted page was clean: dropped without side effects
    Memory failure: 0x827ca68: recovery action for clean LRU page: Recovered
    Memory failure: 0x827ca68: already hardware poisoned
    mce: Memory error not recovered

To fix it, return 0 for "corrupted page was clean", preventing an
unnecessary SIGBUS to user process.

[1] https://lore.kernel.org/lkml/20250217063335.22257-1-xueshuai@linux.alibaba.com/T/#mba94f1305b3009dd340ce4114d3221fe810d1871
Link: https://lkml.kernel.org/r/20250312112852.82415-3-xueshuai@linux.alibaba.com
Fixes: 046545a661 ("mm/hwpoison: fix error page recovered but reported "not recovered"")
Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
Tested-by: Tony Luck <tony.luck@intel.com>
Acked-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ruidong Tian <tianruidong@linux.alibaba.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Yazen Ghannam <yazen.ghannam@amd.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-04-25 10:43:42 +02:00
arch sparc/mm: disable preemption in lazy mmu mode 2025-04-25 10:43:42 +02:00
block block, bfq: fix re-introduced UAF in bic_set_bfqq() 2025-03-28 21:59:02 +01:00
certs certs: Fix build error when PKCS#11 URI contains semicolon 2023-02-09 11:28:11 +01:00
crypto crypto: api - Add crypto_clone_tfm 2024-12-14 19:53:51 +01:00
Documentation sched/isolation: Prevent boot crash when the boot CPU is nohz_full 2025-03-28 21:58:48 +01:00
drivers mtd: rawnand: Add status chack in r852_ready() 2025-04-25 10:43:41 +02:00
fs btrfs: fix non-empty delayed iputs list on unmount due to compressed write workers 2025-04-25 10:43:42 +02:00
include tpm, tpm_tis: Workaround failed command reception on Infineon devices 2025-04-25 10:43:34 +02:00
init rust: Disallow BTF generation with Rust + LTO 2025-03-28 21:58:57 +01:00
io_uring io_uring/kbuf: reject zero sized provided buffers 2025-04-25 10:43:39 +02:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-14 19:54:06 +01:00
kernel locking/lockdep: Decrease nr_unused_locks if lock unused in zap_class() 2025-04-25 10:43:41 +02:00
lib lib: scatterlist: fix sg_split_phys to preserve original scatterlist offsets 2025-04-25 10:43:41 +02:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm/hwpoison: do not send SIGBUS to processes with recovered clean pages 2025-04-25 10:43:42 +02:00
net mptcp: only inc MPJoinAckHMacFailure for HMAC failures 2025-04-25 10:43:41 +02:00
rust scripts: generate_rust_analyzer: provide cfgs for core and alloc 2025-03-28 21:58:57 +01:00
samples samples/landlock: Fix possible NULL dereference in parse_path() 2025-02-21 13:49:03 +01:00
scripts selinux: Chain up tool resolving errors in install_policy.sh 2025-04-10 14:33:30 +02:00
security smack: dont compile ipv6 code unless ipv6 is configured 2025-04-10 14:33:30 +02:00
sound ASoC: qdsp6: q6asm-dai: fix q6asm_dai_compr_set_params error path 2025-04-25 10:43:39 +02:00
tools ktest: Fix Test Failures Due to Missing LOG_FILE Directories 2025-04-25 10:43:34 +02:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin() 2024-06-27 13:46:21 +02:00
.clang-format inet: ping: use hlist_nulls rcu iterator during lookup 2022-12-01 12:42:46 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Remove *.orig pattern from .gitignore 2024-10-17 15:21:15 +02:00
.mailmap 9 hotfixes. 6 for MM, 3 for other areas. Four of these patches address 2022-12-10 17:10:52 -08:00
.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 MAINTAINERS: Remove Michal Marek from Kbuild maintainers 2022-11-16 14:53:00 +09:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: add leah to 6.1 MAINTAINERS file 2024-05-17 11:56:16 +02:00
Makefile Linux 6.1.134 2025-04-10 14:33:44 +02:00
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.