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Yosry Ahmed 76b0fef087 KVM: nSVM: Fix and simplify LBR virtualization handling with nested 
commit 8a4821412c upstream.

The current scheme for handling LBRV when nested is used is very
complicated, especially when L1 does not enable LBRV (i.e. does not set
LBR_CTL_ENABLE_MASK).

To avoid copying LBRs between VMCB01 and VMCB02 on every nested
transition, the current implementation switches between using VMCB01 or
VMCB02 as the source of truth for the LBRs while L2 is running. If L2
enables LBR, VMCB02 is used as the source of truth. When L2 disables
LBR, the LBRs are copied to VMCB01 and VMCB01 is used as the source of
truth. This introduces significant complexity, and incorrect behavior in
some cases.

For example, on a nested #VMEXIT, the LBRs are only copied from VMCB02
to VMCB01 if LBRV is enabled in VMCB01. This is because L2's writes to
MSR_IA32_DEBUGCTLMSR to enable LBR are intercepted and propagated to
VMCB01 instead of VMCB02. However, LBRV is only enabled in VMCB02 when
L2 is running.

This means that if L2 enables LBR and exits to L1, the LBRs will not be
propagated from VMCB02 to VMCB01, because LBRV is disabled in VMCB01.

There is no meaningful difference in CPUID rate in L2 when copying LBRs
on every nested transition vs. the current approach, so do the simple
and correct thing and always copy LBRs between VMCB01 and VMCB02 on
nested transitions (when LBRV is disabled by L1). Drop the conditional
LBRs copying in __svm_{enable/disable}_lbrv() as it is now unnecessary.

VMCB02 becomes the only source of truth for LBRs when L2 is running,
regardless of LBRV being enabled by L1, drop svm_get_lbr_vmcb() and use
svm->vmcb directly in its place.

Fixes: 1d5a1b5860 ("KVM: x86: nSVM: correctly virtualize LBR msrs when L2 is running")
Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Link: https://patch.msgid.link/20251108004524.1600006-4-yosry.ahmed@linux.dev
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-12-07 06:25:03 +09:00
arch
block blk-crypto: use BLK_STS_INVAL for alignment errors 2025-12-01 11:43:36 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: essiv - Check ssize for decryption and in-place encryption 2025-10-19 16:33:42 +02:00
Documentation platform/x86: msi-wmi-platform: Fix typo in WMI GUID 2025-12-01 11:43:30 +01:00
drivers usb: gadget: udc: fix use-after-free in usb_gadget_state_work 2025-12-07 06:25:02 +09:00
fs nfsd: Replace clamp_t in nfsd4_get_drc_mem() 2025-12-07 06:25:02 +09:00
include usb: gadget: udc: fix use-after-free in usb_gadget_state_work 2025-12-07 06:25:02 +09:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:33:50 +02:00
io_uring io_uring/napi: fix io_napi_entry RCU accesses 2025-11-24 10:36:06 +01:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:11:22 +01:00
kernel tracing: Fix WARN_ON in tracing_buffers_mmap_close for split VMAs 2025-12-07 06:24:58 +09:00
lib maple_tree: fix tracepoint string pointers 2025-12-01 11:43:39 +01:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm/huge_memory: fix NULL pointer deference when splitting folio 2025-12-07 06:25:02 +09:00
net libceph: replace BUG_ON with bounds check for map->max_osd 2025-12-07 06:25:02 +09:00
rust rust: kbuild: workaround rustdoc doctests modifier bug 2025-11-24 10:36:07 +01:00
samples ftrace/samples: Fix function size computation 2025-09-19 16:35:44 +02:00
scripts kconfig/nconf: Initialize the default locale at startup 2025-12-01 11:43:36 +01:00
security ima: don't clear IMA_DIGSIG flag when setting or removing non-IMA xattr 2025-11-13 15:34:32 -05:00
sound ALSA: usb-audio: Add DSD quirk for LEAK Stereo 230 2025-12-07 06:24:58 +09:00
tools tracing/tools: Fix incorrcet short option in usage text for --threads 2025-12-01 11:43:38 +01:00
usr kbuild: uapi: Strip comments before size type check 2025-11-13 15:34:35 -05:00
virt KVM: guest_memfd: Remove bindings on memslot deletion when gmem is dying 2025-11-24 10:36:06 +01:00
.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 2025-08-01 09:48:44 +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 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 staging: rtl8712: Remove driver using deprecated API wext 2025-12-07 06:25:02 +09:00
Makefile Linux 6.12.60 2025-12-01 11:43:41 +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.