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Sean Christopherson 433265870a KVM: SVM: Manually context switch DEBUGCTL if LBR virtualization is disabled 
Manually load the guest's DEBUGCTL prior to VMRUN (and restore the host's
value on #VMEXIT) if it diverges from the host's value and LBR
virtualization is disabled, as hardware only context switches DEBUGCTL if
LBR virtualization is fully enabled.  Running the guest with the host's
value has likely been mildly problematic for quite some time, e.g. it will
result in undesirable behavior if BTF diverges (with the caveat that KVM
now suppresses guest BTF due to lack of support).

But the bug became fatal with the introduction of Bus Lock Trap ("Detect"
in kernel paralance) support for AMD (commit 408eb7417a
("x86/bus_lock: Add support for AMD")), as a bus lock in the guest will
trigger an unexpected #DB.

Note, suppressing the bus lock #DB, i.e. simply resuming the guest without
injecting a #DB, is not an option.  It wouldn't address the general issue
with DEBUGCTL, e.g. for things like BTF, and there are other guest-visible
side effects if BusLockTrap is left enabled.

If BusLockTrap is disabled, then DR6.BLD is reserved-to-1; any attempts to
clear it by software are ignored.  But if BusLockTrap is enabled, software
can clear DR6.BLD:

  Software enables bus lock trap by setting DebugCtl MSR[BLCKDB] (bit 2)
  to 1.  When bus lock trap is enabled, ... The processor indicates that
  this #DB was caused by a bus lock by clearing DR6[BLD] (bit 11).  DR6[11]
  previously had been defined to be always 1.

and clearing DR6.BLD is "sticky" in that it's not set (i.e. lowered) by
other #DBs:

  All other #DB exceptions leave DR6[BLD] unmodified

E.g. leaving BusLockTrap enable can confuse a legacy guest that writes '0'
to reset DR6.

Reported-by: rangemachine@gmail.com
Reported-by: whanos@sergal.fun
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219787
Closes: https://lore.kernel.org/all/bug-219787-28872@https.bugzilla.kernel.org%2F
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: stable@vger.kernel.org
Reviewed-and-tested-by: Ravi Bangoria <ravi.bangoria@amd.com>
Link: https://lore.kernel.org/r/20250227222411.3490595-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
2025-02-28 09:17:45 -08:00
arch KVM: SVM: Manually context switch DEBUGCTL if LBR virtualization is disabled 2025-02-28 09:17:45 -08:00
block block-6.14-20250131 2025-01-31 11:49:30 -08:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
Documentation ARM: 2025-02-09 09:41:38 -08:00
drivers Additional power management fix for 6.14-rc2 2025-02-09 09:47:06 -08:00
fs four SMB3 client fixes, 3 DFS related 2025-02-07 19:23:06 -08:00
include Kbuild fixes for v6.14 2025-02-09 10:05:32 -08:00
init Kbuild updates for v6.14 2025-01-31 12:07:07 -08:00
io_uring Fix a dangling pointer bug in the futex code used by the 2025-02-08 10:54:11 -08:00
ipc treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
kernel seccomp fix for v6.14-rc2 2025-02-08 14:04:21 -08:00
lib hardening fixes for v6.14-rc2 2025-02-08 14:12:17 -08:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm assorted stuff for this merge window 2025-02-01 15:07:56 -08:00
net vfs-6.14-rc2.fixes 2025-02-07 09:22:31 -08:00
rust rust: kbuild: do not export generated KASAN ODR symbols 2025-02-06 19:47:04 +01:00
samples AT_EXECVE_CHECK update for v6.14-rc1 (fix1) 2025-01-31 17:12:31 -08:00
scripts Kbuild fixes for v6.14 2025-02-09 10:05:32 -08:00
security treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
sound sound fixes for 6.14-rc1 2025-01-31 09:17:02 -08:00
tools KVM: selftests: Assert that STI blocking isn't set after event injection 2025-02-28 09:15:23 -08:00
usr kbuild: Drop support for include/asm-<arch> in headers_check.pl 2024-12-21 11:43:17 +09:00
virt KVM: remove kvm_arch_post_init_vm 2025-02-04 11:27:45 -05:00
.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: give Clippy the minimum supported Rust version 2025-01-10 00:17:25 +01:00
.cocciconfig
.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 rust: use host dylib naming convention to support macOS 2025-01-10 01:01:24 +01:00
.mailmap 21 hotfixes. 8 are cc:stable and the remainder address post-6.13 issues. 2025-02-01 09:49:20 -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: Move Pavel to kernel.org address 2025-02-07 09:12:33 -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 gpio fixes for v6.14-rc2 2025-02-07 09:50:33 -08:00
Makefile Linux 6.14-rc2 2025-02-09 12:45:03 -08:00
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.