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Maxim Levitsky 244e4e60e3 KVM: x86: Don't clear async #PF queue when CR0.PG is disabled (e.g. on #SMI) 
commit ab4e41eb9f upstream.

Fix an interaction between SMM and PV asynchronous #PFs where an #SMI can
cause KVM to drop an async #PF ready event, and thus result in guest tasks
becoming permanently stuck due to the task that encountered the #PF never
being resumed.  Specifically, don't clear the completion queue when paging
is disabled, and re-check for completed async #PFs if/when paging is
enabled.

Prior to commit 2635b5c4a0 ("KVM: x86: interrupt based APF 'page ready'
event delivery"), flushing the APF queue without notifying the guest of
completed APF requests when paging is disabled was "necessary", in that
delivering a #PF to the guest when paging is disabled would likely confuse
and/or crash the guest.  And presumably the original async #PF development
assumed that a guest would only disable paging when there was no intent to
ever re-enable paging.

That assumption fails in several scenarios, most visibly on an emulated
SMI, as entering SMM always disables CR0.PG (i.e. initially runs with
paging disabled).  When the SMM handler eventually executes RSM, the
interrupted paging-enabled is restored, and the async #PF event is lost.

Similarly, invoking firmware, e.g. via EFI runtime calls, might require a
transition through paging modes and thus also disable paging with valid
entries in the competion queue.

To avoid dropping completion events, drop the "clear" entirely, and handle
paging-enable transitions in the same way KVM already handles APIC
enable/disable events: if a vCPU's APIC is disabled, APF completion events
are not kept pending and not injected while APIC is disabled.  Once a
vCPU's APIC is re-enabled, KVM raises KVM_REQ_APF_READY so that the vCPU
recognizes any pending pending #APF ready events.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20251015033258.50974-4-mlevitsk@redhat.com
[sean: rework changelog to call out #PF injection, drop "real mode"
       references, expand the code comment]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2026-01-08 10:14:21 +01:00
arch KVM: x86: Don't clear async #PF queue when CR0.PG is disabled (e.g. on #SMI) 2026-01-08 10:14:21 +01:00
block block: rate-limit capacity change info log 2026-01-08 10:14:14 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: asymmetric_keys - prevent overflow in asymmetric_key_generate_id 2025-12-18 13:54:47 +01:00
Documentation nfsd: rename nfsd_serv_ prefixed methods and variables with nfsd_net_ 2026-01-08 10:14:09 +01:00
drivers media: vidtv: initialize local pointers upon transfer of memory ownership 2026-01-08 10:14:21 +01:00
fs ocfs2: fix kernel BUG in ocfs2_find_victim_chain 2026-01-08 10:14:21 +01:00
include media: v4l2-mem2mem: Fix outdated documentation 2026-01-08 10:14:16 +01:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:33:50 +02:00
io_uring io_uring: fix filename leak in __io_openat_prep() 2026-01-08 10:14:13 +01:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:11:22 +01:00
kernel kallsyms: Fix wrong "big" kernel symbol type read from procfs 2026-01-08 10:14:14 +01:00
lib lib/vsprintf: Check pointer before dereferencing in time_and_date() 2025-12-18 13:54:57 +01:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm shmem: fix recovery on rename failures 2026-01-08 10:13:54 +01:00
net mptcp: avoid deadlock on fallback while reinjecting 2026-01-08 10:14:16 +01:00
rust rust: kbuild: workaround rustdoc doctests modifier bug 2025-11-24 10:36:07 +01:00
samples samples: work around glibc redefining some of our defines wrong 2025-12-12 18:37:21 +01:00
scripts kbuild: Use objtree for module signing key path 2026-01-08 10:13:56 +01:00
security KEYS: trusted: Fix a memory leak in tpm2_load_cmd 2026-01-08 10:14:13 +01:00
sound ASoC: ak4458: remove the reset operation in probe and remove 2026-01-08 10:14:08 +01:00
tools tools/testing/nvdimm: Use per-DIMM device handle 2026-01-08 10:14:20 +01:00
usr kbuild: uapi: Strip comments before size type check 2025-11-13 15:34:35 -05:00
virt KVM: Disallow toggling KVM_MEM_GUEST_MEMFD on an existing memslot 2026-01-08 10:14:21 +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 6.12.63 2025-12-18 13:55:23 +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.