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[ Upstream commit64d6820d64] Userspace can play some dirty tricks on us by selecting a given PMU version (such as PMUv3p5), restore a PMCR_EL0 value that has PMCR_EL0.LP set, and then switch the PMU version to PMUv3p1, for example. In this situation, we end-up with PMCR_EL0.LP being set and spreading havoc in the PMU emulation. This is specially hard as the first two step can be done on one vcpu and the third step on another, meaning that we need to sanitise *all* vcpus when the PMU version is changed. In orer to avoid a pretty complicated locking situation, defer the sanitisation of PMCR_EL0 to the point where the vcpu is actually run for the first tine, using the existing KVM_REQ_RELOAD_PMU request that calls into kvm_pmu_handle_pmcr(). There is still an obscure corner case where userspace could do the above trick, and then save the VM without running it. They would then observe an inconsistent state (PMUv3.1 + LP set), but that state will be fixed on the first run anyway whenever the guest gets restored on a host. Reported-by: Reiji Watanabe <reijiw@google.com> Signed-off-by: Marc Zyngier <maz@kernel.org> Stable-dep-of:f6da81f650("KVM: arm64: PMU: Don't save PMCR_EL0.{C,P} for the vCPU") Signed-off-by: Sasha Levin <sashal@kernel.org>
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.