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Marc Zyngier f616506754 KVM: arm64: vgic: Don't hold config_lock while unregistering redistributors
We recently moved the teardown of the vgic part of a vcpu inside
a critical section guarded by the config_lock. This teardown phase
involves calling into kvm_io_bus_unregister_dev(), which takes the
kvm->srcu lock.

However, this violates the established order where kvm->srcu is
taken on a memory fault (such as an MMIO access), possibly
followed by taking the config_lock if the GIC emulation requires
mutual exclusion from the other vcpus.

It therefore results in a bad lockdep splat, as reported by Zenghui.

Fix this by moving the call to kvm_io_bus_unregister_dev() outside
of the config_lock critical section. At this stage, there shouln't
be any need to hold the config_lock.

As an additional bonus, document the ordering between kvm->slots_lock,
kvm->srcu and kvm->arch.config_lock so that I cannot pretend I didn't
know about those anymore.

Fixes: 9eb18136af ("KVM: arm64: vgic: Hold config_lock while tearing down a CPU interface")
Reported-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
Tested-by: Zenghui Yu <yuzenghui@huawei.com>
Link: https://lore.kernel.org/r/20240819125045.3474845-1-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
History 2024-08-19 17:05:21 +00:00
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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.