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Now that the PMU is refreshed when MSR_IA32_PERF_CAPABILITIES is written by host userspace, zero out the number of LBR records for a vCPU during PMU refresh if PMU_CAP_LBR_FMT is not set in PERF_CAPABILITIES instead of handling the check at run-time. guest_cpuid_has() is expensive due to the linear search of guest CPUID entries, intel_pmu_lbr_is_enabled() is checked on every VM-Enter, _and_ simply enumerating the same "Model" as the host causes KVM to set the number of LBR records to a non-zero value. Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20220727233424.2968356-4-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.