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Sean Christopherson 004a0aa56e KVM: x86/pmu: Snapshot and clear reprogramming bitmap before reprogramming
Refactor the handling of the reprogramming bitmap to snapshot and clear
to-be-processed bits before doing the reprogramming, and then explicitly
set bits for PMCs that need to be reprogrammed (again).  This will allow
adding a macro to iterate over all valid PMCs without having to add
special handling for the reprogramming bit, which (a) can have bits set
for non-existent PMCs and (b) needs to clear such bits to avoid wasting
cycles in perpetuity.

Note, the existing behavior of clearing bits after reprogramming does NOT
have a race with kvm_vm_ioctl_set_pmu_event_filter().  Setting a new PMU
filter synchronizes SRCU _before_ setting the bitmap, i.e. guarantees that
the vCPU isn't in the middle of reprogramming with a stale filter prior to
setting the bitmap.

Link: https://lore.kernel.org/r/20231110022857.1273836-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
History 2024-02-01 09:35:48 -08:00
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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 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.