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Set the min_level for the TDP iterator at the root level when zapping all SPTEs to optimize the iterator's try_step_down(). Zapping a non-leaf SPTE will recursively zap all its children, thus there is no need for the iterator to attempt to step down. This avoids rereading the top-level SPTEs after they are zapped by causing try_step_down() to short-circuit. In most cases, optimizing try_step_down() will be in the noise as the cost of zapping SPTEs completely dominates the overall time. The optimization is however helpful if the zap occurs with relatively few SPTEs, e.g. if KVM is zapping in response to multiple memslot updates when userspace is adding and removing read-only memslots for option ROMs. In that case, the task doing the zapping likely isn't a vCPU thread, but it still holds mmu_lock for read and thus can be a noisy neighbor of sorts. Reviewed-by: Ben Gardon <bgardon@google.com> Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20210812181414.3376143-3-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.