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Sean Christopherson 44ee0afc9d perf/x86/intel: KVM: Mask PEBS_ENABLE loaded for guest with vCPU's value. 
commit 58f6217e5d upstream.

When generating the MSR_IA32_PEBS_ENABLE value that will be loaded on
VM-Entry to a KVM guest, mask the value with the vCPU's desired PEBS_ENABLE
value.  Consulting only the host kernel's host vs. guest masks results in
running the guest with PEBS enabled even when the guest doesn't want to use
PEBS.  Because KVM uses perf events to proxy the guest virtual PMU, simply
looking at exclude_host can't differentiate between events created by host
userspace, and events created by KVM on behalf of the guest.

Running the guest with PEBS unexpectedly enabled typically manifests as
crashes due to a near-infinite stream of #PFs.  E.g. if the guest hasn't
written MSR_IA32_DS_AREA, the CPU will hit page faults on address '0' when
trying to record PEBS events.

The issue is most easily reproduced by running `perf kvm top` from before
commit 7b100989b4 ("perf evlist: Remove __evlist__add_default") (after
which, `perf kvm top` effectively stopped using PEBS).	The userspace side
of perf creates a guest-only PEBS event, which intel_guest_get_msrs()
misconstrues a guest-*owned* PEBS event.

Arguably, this is a userspace bug, as enabling PEBS on guest-only events
simply cannot work, and userspace can kill VMs in many other ways (there
is no danger to the host).  However, even if this is considered to be bad
userspace behavior, there's zero downside to perf/KVM restricting PEBS to
guest-owned events.

Note, commit 854250329c ("KVM: x86/pmu: Disable guest PEBS temporarily
in two rare situations") fixed the case where host userspace is profiling
KVM *and* userspace, but missed the case where userspace is profiling only
KVM.

Fixes: c59a1f106f ("KVM: x86/pmu: Add IA32_PEBS_ENABLE MSR emulation for extended PEBS")
Closes: https://lore.kernel.org/all/Z_VUswFkWiTYI0eD@do-x1carbon
Reported-by: Seth Forshee <sforshee@kernel.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Tested-by: "Seth Forshee (DigitalOcean)" <sforshee@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20250426001355.1026530-1-seanjc@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-05-09 09:50:31 +02:00
arch perf/x86/intel: KVM: Mask PEBS_ENABLE loaded for guest with vCPU's value. 2025-05-09 09:50:31 +02:00
block mq-deadline: don't call req_get_ioprio from the I/O completion handler 2025-05-02 07:59:33 +02:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: Kconfig - Select LIB generic option 2025-05-02 07:59:33 +02:00
Documentation bpf: Add namespace to BPF internal symbols 2025-05-02 07:59:04 +02:00
drivers i2c: imx-lpi2c: Fix clock count when probe defers 2025-05-09 09:50:31 +02:00
fs btrfs: fix COW handling in run_delalloc_nocow() 2025-05-09 09:50:30 +02:00
include netfilter: fib: avoid lookup if socket is available 2025-05-02 07:59:05 +02:00
init sched/isolation: Make CONFIG_CPU_ISOLATION depend on CONFIG_SMP 2025-05-02 07:59:21 +02:00
io_uring io_uring: always do atomic put from iowq 2025-05-02 07:59:21 +02:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-05 14:03:02 +01:00
kernel bpf: Fix BPF_INTERNAL namespace import 2025-05-05 11:00:29 +02:00
lib crypto: lib/Kconfig - Hide arch options from user 2025-05-02 07:59:32 +02:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm/vmscan: don't try to reclaim hwpoison folio 2025-05-02 07:58:52 +02:00
net 9p/trans_fd: mark concurrent read and writes to p9_conn->err 2025-05-02 07:59:20 +02:00
rust rust: firmware: Use ffi::c_char type in FwFunc 2025-05-02 07:59:06 +02:00
samples tracing: Verify event formats that have "%*p.." 2025-05-02 07:58:52 +02:00
scripts objtool: Silence more KCOV warnings, part 2 2025-05-02 07:59:33 +02:00
security landlock: Prepare to add second errata 2025-04-20 10:15:56 +02:00
sound ALSA: usb-audio: Add second USB ID for Jabra Evolve 65 headset 2025-05-09 09:50:29 +02:00
tools objtool: Ignore end-of-section jumps for KCOV/GCOV 2025-05-02 07:59:33 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-13 13:02:18 +01:00
virt KVM: Allow building irqbypass.ko as as module when kvm.ko is a module 2025-04-20 10:15:54 +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: enable Clippy's check-private-items 2025-03-13 13:01:42 +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 MAINTAINERS: add entry for the Rust alloc module 2025-03-13 13:01:47 +01:00
Makefile Linux 6.12.27 2025-05-05 11:00:29 +02:00
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.