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Sean Christopherson a75afe480d KVM: Always flush async #PF workqueue when vCPU is being destroyed 
[ Upstream commit 3d75b8aa5c ]

Always flush the per-vCPU async #PF workqueue when a vCPU is clearing its
completion queue, e.g. when a VM and all its vCPUs is being destroyed.
KVM must ensure that none of its workqueue callbacks is running when the
last reference to the KVM _module_ is put.  Gifting a reference to the
associated VM prevents the workqueue callback from dereferencing freed
vCPU/VM memory, but does not prevent the KVM module from being unloaded
before the callback completes.

Drop the misguided VM refcount gifting, as calling kvm_put_kvm() from
async_pf_execute() if kvm_put_kvm() flushes the async #PF workqueue will
result in deadlock.  async_pf_execute() can't return until kvm_put_kvm()
finishes, and kvm_put_kvm() can't return until async_pf_execute() finishes:

 WARNING: CPU: 8 PID: 251 at virt/kvm/kvm_main.c:1435 kvm_put_kvm+0x2d/0x320 [kvm]
 Modules linked in: vhost_net vhost vhost_iotlb tap kvm_intel kvm irqbypass
 CPU: 8 PID: 251 Comm: kworker/8:1 Tainted: G        W          6.6.0-rc1-e7af8d17224a-x86/gmem-vm #119
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
 Workqueue: events async_pf_execute [kvm]
 RIP: 0010:kvm_put_kvm+0x2d/0x320 [kvm]
 Call Trace:
  <TASK>
  async_pf_execute+0x198/0x260 [kvm]
  process_one_work+0x145/0x2d0
  worker_thread+0x27e/0x3a0
  kthread+0xba/0xe0
  ret_from_fork+0x2d/0x50
  ret_from_fork_asm+0x11/0x20
  </TASK>
 ---[ end trace 0000000000000000 ]---
 INFO: task kworker/8:1:251 blocked for more than 120 seconds.
       Tainted: G        W          6.6.0-rc1-e7af8d17224a-x86/gmem-vm #119
 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
 task:kworker/8:1     state:D stack:0     pid:251   ppid:2      flags:0x00004000
 Workqueue: events async_pf_execute [kvm]
 Call Trace:
  <TASK>
  __schedule+0x33f/0xa40
  schedule+0x53/0xc0
  schedule_timeout+0x12a/0x140
  __wait_for_common+0x8d/0x1d0
  __flush_work.isra.0+0x19f/0x2c0
  kvm_clear_async_pf_completion_queue+0x129/0x190 [kvm]
  kvm_arch_destroy_vm+0x78/0x1b0 [kvm]
  kvm_put_kvm+0x1c1/0x320 [kvm]
  async_pf_execute+0x198/0x260 [kvm]
  process_one_work+0x145/0x2d0
  worker_thread+0x27e/0x3a0
  kthread+0xba/0xe0
  ret_from_fork+0x2d/0x50
  ret_from_fork_asm+0x11/0x20
  </TASK>

If kvm_clear_async_pf_completion_queue() actually flushes the workqueue,
then there's no need to gift async_pf_execute() a reference because all
invocations of async_pf_execute() will be forced to complete before the
vCPU and its VM are destroyed/freed.  And that in turn fixes the module
unloading bug as __fput() won't do module_put() on the last vCPU reference
until the vCPU has been freed, e.g. if closing the vCPU file also puts the
last reference to the KVM module.

Note that kvm_check_async_pf_completion() may also take the work item off
the completion queue and so also needs to flush the work queue, as the
work will not be seen by kvm_clear_async_pf_completion_queue().  Waiting
on the workqueue could theoretically delay a vCPU due to waiting for the
work to complete, but that's a very, very small chance, and likely a very
small delay.  kvm_arch_async_page_present_queued() unconditionally makes a
new request, i.e. will effectively delay entering the guest, so the
remaining work is really just:

        trace_kvm_async_pf_completed(addr, cr2_or_gpa);

        __kvm_vcpu_wake_up(vcpu);

        mmput(mm);

and mmput() can't drop the last reference to the page tables if the vCPU is
still alive, i.e. the vCPU won't get stuck tearing down page tables.

Add a helper to do the flushing, specifically to deal with "wakeup all"
work items, as they aren't actually work items, i.e. are never placed in a
workqueue.  Trying to flush a bogus workqueue entry rightly makes
__flush_work() complain (kudos to whoever added that sanity check).

Note, commit 5f6de5cbeb ("KVM: Prevent module exit until all VMs are
freed") *tried* to fix the module refcounting issue by having VMs grab a
reference to the module, but that only made the bug slightly harder to hit
as it gave async_pf_execute() a bit more time to complete before the KVM
module could be unloaded.

Fixes: af585b921e ("KVM: Halt vcpu if page it tries to access is swapped out")
Cc: stable@vger.kernel.org
Cc: David Matlack <dmatlack@google.com>
Reviewed-by: Xu Yilun <yilun.xu@intel.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/20240110011533.503302-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
 		2024-04-03 15:28:18 +02:00
Documentation media: mc: Expand MUST_CONNECT flag to always require an enabled link 2024-04-03 15:28:17 +02:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
arch arm: dts: marvell: Fix maxium->maxim typo in brownstone dts 2024-04-03 15:28:16 +02:00
block block: Provide bdev_open_* functions 2024-03-26 18:19:40 -04:00
certs certs: Reference revocation list for all keyrings 2023-08-17 20:12:41 +00:00
crypto crypto: jitter - fix CRYPTO_JITTERENTROPY help text 2024-03-26 18:19:52 -04:00
drivers media: nxp: imx8-isi: Mark all crossbar sink pads as MUST_CONNECT 2024-04-03 15:28:18 +02:00
fs ceph: stop copying to iter at EOF on sync reads 2024-03-26 18:20:11 -04:00
include media: mc: Add num_links flag to media_pad 2024-04-03 15:28:17 +02:00
init modules: wait do_free_init correctly 2024-03-26 18:19:55 -04:00
io_uring io_uring: fix poll_remove stalled req completion 2024-03-26 18:20:09 -04:00
ipc Add x86 shadow stack support 2023-08-31 12:20:12 -07:00
kernel bpf: report RCU QS in cpumap kthread 2024-03-26 18:20:12 -04:00
lib pci_iounmap(): Fix MMIO mapping leak 2024-04-03 15:28:17 +02:00
mm quota: Properly annotate i_dquot arrays with __rcu 2024-03-26 18:19:46 -04:00
net netfilter: nf_tables: Fix a memory leak in nf_tables_updchain 2024-03-26 18:20:13 -04:00
rust rust: upgrade to Rust 1.73.0 2024-02-16 19:10:43 +01:00
samples work around gcc bugs with 'asm goto' with outputs 2024-02-23 09:24:47 +01:00
scripts kconfig: fix infinite loop when expanding a macro at the end of file 2024-03-26 18:20:05 -04:00
security smack: Handle SMACK64TRANSMUTE in smack_inode_setsecurity() 2024-04-03 15:28:16 +02:00
sound ASoC: rockchip: i2s-tdm: Fix inaccurate sampling rates 2024-03-26 18:20:07 -04:00
tools selftests: forwarding: Fix ping failure due to short timeout 2024-03-26 18:20:13 -04:00
usr initramfs: Encode dependency on KBUILD_BUILD_TIMESTAMP 2023-06-06 17:54:49 +09:00
virt KVM: Always flush async #PF workqueue when vCPU is being destroyed 2024-04-03 15:28:18 +02:00
.clang-format iommu: Add for_each_group_device() 2023-05-23 08:15:51 +02:00
.cocciconfig
…
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: rpm-pkg: rename binkernel.spec to kernel.spec 2023-07-25 00:59:33 +09:00
.mailmap 20 hotfixes. 12 are cc:stable and the remainder address post-6.5 issues 2023-10-24 09:52:16 -10:00
.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 USB: Remove Wireless USB and UWB documentation 2023-08-09 14:17:32 +02:00
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 Catherine as xfs maintainer for 6.6.y 2024-02-16 19:10:43 +01:00
Makefile Linux 6.6.23 2024-03-26 18:22:53 -04:00
README
…

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 Restructured Text 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.