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Do not clear manipulate MSR_IA32_PERF_CAPABILITIES in intel_pmu_refresh(), i.e. give userspace full control over capability/read-only MSRs. KVM is not a babysitter, it is userspace's responsiblity to provide a valid and coherent vCPU model. Attempting to "help" the guest by forcing a consistent model creates edge cases, and ironicially leads to inconsistent behavior. Example #1: KVM doesn't do intel_pmu_refresh() when userspace writes the MSR. Example #2: KVM doesn't clear the bits when the PMU is disabled, or when there's no architectural PMU. Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20220611005755.753273-3-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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.