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Sean Christopherson b4d37cdb77 KVM: Don't clobber irqfd routing type when deassigning irqfd
When deassigning a KVM_IRQFD, don't clobber the irqfd's copy of the IRQ's
routing entry as doing so breaks kvm_arch_irq_bypass_del_producer() on x86
and arm64, which explicitly look for KVM_IRQ_ROUTING_MSI.  Instead, to
handle a concurrent routing update, verify that the irqfd is still active
before consuming the routing information.  As evidenced by the x86 and
arm64 bugs, and another bug in kvm_arch_update_irqfd_routing() (see below),
clobbering the entry type without notifying arch code is surprising and
error prone.

As a bonus, checking that the irqfd is active provides a convenient
location for documenting _why_ KVM must not consume the routing entry for
an irqfd that is in the process of being deassigned: once the irqfd is
deleted from the list (which happens *before* the eventfd is detached), it
will no longer receive updates via kvm_irq_routing_update(), and so KVM
could deliver an event using stale routing information (relative to
KVM_SET_GSI_ROUTING returning to userspace).

As an even better bonus, explicitly checking for the irqfd being active
fixes a similar bug to the one the clobbering is trying to prevent: if an
irqfd is deactivated, and then its routing is changed,
kvm_irq_routing_update() won't invoke kvm_arch_update_irqfd_routing()
(because the irqfd isn't in the list).  And so if the irqfd is in bypass
mode, IRQs will continue to be posted using the old routing information.

As for kvm_arch_irq_bypass_del_producer(), clobbering the routing type
results in KVM incorrectly keeping the IRQ in bypass mode, which is
especially problematic on AMD as KVM tracks IRQs that are being posted to
a vCPU in a list whose lifetime is tied to the irqfd.

Without the help of KASAN to detect use-after-free, the most common
sympton on AMD is a NULL pointer deref in amd_iommu_update_ga() due to
the memory for irqfd structure being re-allocated and zeroed, resulting
in irqfd->irq_bypass_data being NULL when read by
avic_update_iommu_vcpu_affinity():

  BUG: kernel NULL pointer dereference, address: 0000000000000018
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 40cf2b9067 P4D 40cf2b9067 PUD 408362a067 PMD 0
  Oops: Oops: 0000 [#1] SMP
  CPU: 6 UID: 0 PID: 40383 Comm: vfio_irq_test
  Tainted: G     U  W  O        6.19.0-smp--5dddc257e6b2-irqfd #31 NONE
  Tainted: [U]=USER, [W]=WARN, [O]=OOT_MODULE
  Hardware name: Google, Inc. Arcadia_IT_80/Arcadia_IT_80, BIOS 34.78.2-0 09/05/2025
  RIP: 0010:amd_iommu_update_ga+0x19/0xe0
  Call Trace:
   <TASK>
   avic_update_iommu_vcpu_affinity+0x3d/0x90 [kvm_amd]
   __avic_vcpu_load+0xf4/0x130 [kvm_amd]
   kvm_arch_vcpu_load+0x89/0x210 [kvm]
   vcpu_load+0x30/0x40 [kvm]
   kvm_arch_vcpu_ioctl_run+0x45/0x620 [kvm]
   kvm_vcpu_ioctl+0x571/0x6a0 [kvm]
   __se_sys_ioctl+0x6d/0xb0
   do_syscall_64+0x6f/0x9d0
   entry_SYSCALL_64_after_hwframe+0x4b/0x53
  RIP: 0033:0x46893b
    </TASK>
  ---[ end trace 0000000000000000 ]---

If AVIC is inhibited when the irfd is deassigned, the bug will manifest as
list corruption, e.g. on the next irqfd assignment.

  list_add corruption. next->prev should be prev (ffff8d474d5cd588),
                       but was 0000000000000000. (next=ffff8d8658f86530).
  ------------[ cut here ]------------
  kernel BUG at lib/list_debug.c:31!
  Oops: invalid opcode: 0000 [#1] SMP
  CPU: 128 UID: 0 PID: 80818 Comm: vfio_irq_test
  Tainted: G     U  W  O        6.19.0-smp--f19dc4d680ba-irqfd #28 NONE
  Tainted: [U]=USER, [W]=WARN, [O]=OOT_MODULE
  Hardware name: Google, Inc. Arcadia_IT_80/Arcadia_IT_80, BIOS 34.78.2-0 09/05/2025
  RIP: 0010:__list_add_valid_or_report+0x97/0xc0
  Call Trace:
   <TASK>
   avic_pi_update_irte+0x28e/0x2b0 [kvm_amd]
   kvm_pi_update_irte+0xbf/0x190 [kvm]
   kvm_arch_irq_bypass_add_producer+0x72/0x90 [kvm]
   irq_bypass_register_consumer+0xcd/0x170 [irqbypass]
   kvm_irqfd+0x4c6/0x540 [kvm]
   kvm_vm_ioctl+0x118/0x5d0 [kvm]
   __se_sys_ioctl+0x6d/0xb0
   do_syscall_64+0x6f/0x9d0
   entry_SYSCALL_64_after_hwframe+0x4b/0x53
   </TASK>
  ---[ end trace 0000000000000000 ]---

On Intel and arm64, the bug is less noisy, as the end result is that the
device keeps posting IRQs to the vCPU even after it's been deassigned.

Note, the worst of the breakage can be traced back to commit cb21073767
("KVM: Pass new routing entries and irqfd when updating IRTEs"), as before
that commit KVM would pull the routing information from the per-VM routing
table.  But as above, similar bugs have existed since support for IRQ
bypass was added.  E.g. if a routing change finished before irq_shutdown()
invoked kvm_arch_irq_bypass_del_producer(), VMX and SVM would see stale
routing information and potentially leave the irqfd in bypass mode.

Alternatively, x86 could be fixed by explicitly checking irq_bypass_vcpu
instead of irq_entry.type in kvm_arch_irq_bypass_del_producer(), and arm64
could be modified to utilize irq_bypass_vcpu in a similar manner.  But (a)
that wouldn't fix the routing updates bug, and (b) fixing core code doesn't
preclude x86 (or arm64) from adding such code as a sanity check (spoiler
alert).

Fixes: f70c20aaf1 ("KVM: Add an arch specific hooks in 'struct kvm_kernel_irqfd'")
Fixes: cb21073767 ("KVM: Pass new routing entries and irqfd when updating IRTEs")
Fixes: a0d7e2fc61 ("KVM: arm64: vgic-v4: Only attempt vLPI mapping for actual MSIs")
Cc: stable@vger.kernel.org
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oupton@kernel.org>
Link: https://patch.msgid.link/20260113174606.104978-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
2026-01-14 13:17:14 -08:00
arch KVM: SVM: Check vCPU ID against max x2AVIC ID if and only if x2AVIC is enabled 2026-01-14 13:09:50 -08:00
block block-6.19-20251218 2025-12-20 09:48:56 -08:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: seqiv - Do not use req->iv after crypto_aead_encrypt 2025-12-19 14:47:06 +08:00
Documentation RISC-V updates for v6.19-rc3 2025-12-28 09:44:26 -08:00
drivers Including fixes from Bluetooth and WiFi. Notably this includes the fix 2025-12-30 08:45:58 -08:00
fs nfsd-6.19 fixes: 2025-12-30 17:56:26 -08:00
include Including fixes from Bluetooth and WiFi. Notably this includes the fix 2025-12-30 08:45:58 -08:00
init Significant patch series in this pull request: 2025-12-06 14:01:20 -08:00
io_uring io_uring-6.19-20251226 2025-12-26 11:34:38 -08:00
ipc Significant patch series in this pull request: 2025-12-06 14:01:20 -08:00
kernel 27 hotfixes. 12 are cc:stable, 18 are MM. 2025-12-29 11:40:38 -08:00
lib idr: fix idr_alloc() returning an ID out of range 2025-12-23 11:23:11 -08:00
LICENSES LICENSES: Add modern form of the LGPL-2.1 tags to the usage guide section 2025-10-22 07:58:19 +02:00
mm mm/ksm: fix pte_unmap_unlock of wrong address in break_ksm_pmd_entry 2025-12-23 11:23:17 -08:00
net Including fixes from Bluetooth and WiFi. Notably this includes the fix 2025-12-30 08:45:58 -08:00
rust 27 hotfixes. 12 are cc:stable, 18 are MM. 2025-12-29 11:40:38 -08:00
samples samples: rust: fix endianness issue in rust_driver_pci 2025-12-17 18:10:58 +01:00
scripts mcb: Add missing modpost build support 2025-12-27 20:48:01 +01:00
security kernel/kexec: change the prototype of kimage_map_segment() 2025-12-23 11:23:13 -08:00
sound ALSA: hda/realtek: fix PCI SSID for one of the HP 200 G2i laptop 2025-12-21 11:19:31 +01:00
tools selftests: kvm: Verify TILELOADD actually #NM faults when XFD[18]=1 2026-01-10 07:17:30 +01:00
usr initramfs: add gen_init_cpio to hostprogs unconditionally 2025-11-26 21:55:40 +01:00
virt KVM: Don't clobber irqfd routing type when deassigning irqfd 2026-01-14 13:17:14 -08:00
.clang-format s390/pci: Fix cyclic dead-lock in zpci_zdev_put() and zpci_scan_devices() 2025-12-14 11:03:58 +01:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +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 MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: kbuild: add proc macro library support 2025-11-24 17:15:36 +01:00
.mailmap .mailmap: remove one of the entries for WangYuli 2025-12-23 11:23:13 -08:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.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 Including fixes from netfilter and CAN. 2025-12-19 07:55:35 +12:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS 27 hotfixes. 12 are cc:stable, 18 are MM. 2025-12-29 11:40:38 -08:00
Makefile Linux 6.19-rc3 2025-12-28 13:24:26 -08:00
README README: restructure with role-based documentation and guidelines 2025-11-29 08:40:33 -07:00

Linux kernel
============

The Linux kernel is the core of any Linux operating system. It manages hardware,
system resources, and provides the fundamental services for all other software.

Quick Start
-----------

* Report a bug: See Documentation/admin-guide/reporting-issues.rst
* Get the latest kernel: https://kernel.org
* Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst
* Join the community: https://lore.kernel.org/

Essential Documentation
-----------------------

All users should be familiar with:

* Building requirements: Documentation/process/changes.rst
* Code of Conduct: Documentation/process/code-of-conduct.rst
* License: See COPYING

Documentation can be built with make htmldocs or viewed online at:
https://www.kernel.org/doc/html/latest/


Who Are You?
============

Find your role below:

* New Kernel Developer - Getting started with kernel development
* Academic Researcher - Studying kernel internals and architecture
* Security Expert - Hardening and vulnerability analysis
* Backport/Maintenance Engineer - Maintaining stable kernels
* System Administrator - Configuring and troubleshooting
* Maintainer - Leading subsystems and reviewing patches
* Hardware Vendor - Writing drivers for new hardware
* Distribution Maintainer - Packaging kernels for distros


For Specific Users
==================

New Kernel Developer
--------------------

Welcome! Start your kernel development journey here:

* Getting Started: Documentation/process/development-process.rst
* Your First Patch: Documentation/process/submitting-patches.rst
* Coding Style: Documentation/process/coding-style.rst
* Build System: Documentation/kbuild/index.rst
* Development Tools: Documentation/dev-tools/index.rst
* Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst
* Core APIs: Documentation/core-api/index.rst

Academic Researcher
-------------------

Explore the kernel's architecture and internals:

* Researcher Guidelines: Documentation/process/researcher-guidelines.rst
* Memory Management: Documentation/mm/index.rst
* Scheduler: Documentation/scheduler/index.rst
* Networking Stack: Documentation/networking/index.rst
* Filesystems: Documentation/filesystems/index.rst
* RCU (Read-Copy Update): Documentation/RCU/index.rst
* Locking Primitives: Documentation/locking/index.rst
* Power Management: Documentation/power/index.rst

Security Expert
---------------

Security documentation and hardening guides:

* Security Documentation: Documentation/security/index.rst
* LSM Development: Documentation/security/lsm-development.rst
* Self Protection: Documentation/security/self-protection.rst
* Reporting Vulnerabilities: Documentation/process/security-bugs.rst
* CVE Procedures: Documentation/process/cve.rst
* Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst
* Security Features: Documentation/userspace-api/seccomp_filter.rst

Backport/Maintenance Engineer
-----------------------------

Maintain and stabilize kernel versions:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* Backporting Guide: Documentation/process/backporting.rst
* Applying Patches: Documentation/process/applying-patches.rst
* Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git for Maintainers: Documentation/maintainer/configure-git.rst

System Administrator
--------------------

Configure, tune, and troubleshoot Linux systems:

* Admin Guide: Documentation/admin-guide/index.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst
* Tracing/Debugging: Documentation/trace/index.rst
* Performance Security: Documentation/admin-guide/perf-security.rst
* Hardware Monitoring: Documentation/hwmon/index.rst

Maintainer
----------

Lead kernel subsystems and manage contributions:

* Maintainer Handbook: Documentation/maintainer/index.rst
* Pull Requests: Documentation/maintainer/pull-requests.rst
* Managing Patches: Documentation/maintainer/modifying-patches.rst
* Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst
* Development Process: Documentation/process/maintainer-handbooks.rst
* Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git Configuration: Documentation/maintainer/configure-git.rst

Hardware Vendor
---------------

Write drivers and support new hardware:

* Driver API Guide: Documentation/driver-api/index.rst
* Driver Model: Documentation/driver-api/driver-model/driver.rst
* Device Drivers: Documentation/driver-api/infrastructure.rst
* Bus Types: Documentation/driver-api/driver-model/bus.rst
* Device Tree Bindings: Documentation/devicetree/bindings/
* Power Management: Documentation/driver-api/pm/index.rst
* DMA API: Documentation/core-api/dma-api.rst

Distribution Maintainer
-----------------------

Package and distribute the kernel:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* ABI Documentation: Documentation/ABI/README
* Kernel Configuration: Documentation/kbuild/kconfig.rst
* Module Signing: Documentation/admin-guide/module-signing.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst



Communication and Support
=========================

* Mailing Lists: https://lore.kernel.org/
* IRC: #kernelnewbies on irc.oftc.net
* Bugzilla: https://bugzilla.kernel.org/
* MAINTAINERS file: Lists subsystem maintainers and mailing lists
* Email Clients: Documentation/process/email-clients.rst