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Xin Li (Intel) 2b9052d88d x86/traps: Initialize DR6 by writing its architectural reset value 
commit 5f465c148c upstream.

Initialize DR6 by writing its architectural reset value to avoid
incorrectly zeroing DR6 to clear DR6.BLD at boot time, which leads
to a false bus lock detected warning.

The Intel SDM says:

  1) Certain debug exceptions may clear bits 0-3 of DR6.

  2) BLD induced #DB clears DR6.BLD and any other debug exception
     doesn't modify DR6.BLD.

  3) RTM induced #DB clears DR6.RTM and any other debug exception
     sets DR6.RTM.

  To avoid confusion in identifying debug exceptions, debug handlers
  should set DR6.BLD and DR6.RTM, and clear other DR6 bits before
  returning.

The DR6 architectural reset value 0xFFFF0FF0, already defined as
macro DR6_RESERVED, satisfies these requirements, so just use it to
reinitialize DR6 whenever needed.

Since clear_all_debug_regs() no longer zeros all debug registers,
rename it to initialize_debug_regs() to better reflect its current
behavior.

Since debug_read_clear_dr6() no longer clears DR6, rename it to
debug_read_reset_dr6() to better reflect its current behavior.

Fixes: ebb1064e7c ("x86/traps: Handle #DB for bus lock")
Reported-by: Sohil Mehta <sohil.mehta@intel.com>
Suggested-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Sohil Mehta <sohil.mehta@intel.com>
Link: https://lore.kernel.org/lkml/06e68373-a92b-472e-8fd9-ba548119770c@intel.com/
Cc:stable@vger.kernel.org
Link: https://lore.kernel.org/all/20250620231504.2676902-2-xin%40zytor.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-07-06 11:01:42 +02:00
arch x86/traps: Initialize DR6 by writing its architectural reset value 2025-07-06 11:01:42 +02:00
block block: Clear BIO_EMULATES_ZONE_APPEND flag on BIO completion 2025-06-27 11:11:19 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: api - Redo lookup on EEXIST 2025-06-19 15:31:30 +02:00
Documentation netlink: specs: tc: replace underscores with dashes in names 2025-07-06 11:01:41 +02:00
drivers EDAC/amd64: Fix size calculation for Non-Power-of-Two DIMMs 2025-07-06 11:01:42 +02:00
fs cifs: Fix reading into an ITER_FOLIOQ from the smbdirect code 2025-07-06 11:01:42 +02:00
include vsock/uapi: fix linux/vm_sockets.h userspace compilation errors 2025-07-06 11:01:40 +02:00
init rust: clean Rust 1.88.0's unnecessary_transmutes lint 2025-05-18 08:24:51 +02:00
io_uring io_uring/sqpoll: don't put task_struct on tctx setup failure 2025-06-27 11:11:42 +01:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:11:22 +01:00
kernel perf/core: Fix WARN in perf_cgroup_switch() 2025-06-27 11:11:45 +01:00
lib lib/group_cpus: fix NULL pointer dereference from group_cpus_evenly() 2025-07-06 11:01:39 +02:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm/damon/sysfs-schemes: free old damon_sysfs_scheme_filter->memcg_path on write 2025-07-06 11:01:38 +02:00
net net: selftests: fix TCP packet checksum 2025-07-06 11:01:41 +02:00
rust rust: arm: fix unknown (to Clang) argument '-mno-fdpic' 2025-07-06 11:01:33 +02:00
samples samples/bpf: Fix compilation failure for samples/bpf on LoongArch Fedora 2025-05-29 11:02:01 +02:00
scripts rust: compile libcore with edition 2024 for 1.87+ 2025-06-27 11:11:40 +01:00
security selinux: fix selinux_xfrm_alloc_user() to set correct ctx_len 2025-06-27 11:11:38 +01:00
sound ALSA: hda/realtek: Fix built-in mic on ASUS VivoBook X507UAR 2025-07-06 11:01:41 +02:00
tools libbpf: Fix possible use-after-free for externs 2025-07-06 11:01:40 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-13 13:02:18 +01:00
virt KVM: Add member to struct kvm_gfn_range to indicate private/shared 2025-05-22 14:29:36 +02:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-18 08:24:51 +02:00
.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 Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -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 self from DSA entry 2024-11-03 12:52:38 -08:00
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: Update Alexey Makhalov's email address 2025-05-22 14:29:46 +02:00
Makefile Linux 6.12.35 2025-06-27 11:11:46 +01:00
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.