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Set SPTEs directly to SHADOW_NONPRESENT_VALUE and batch up TLB flushes when zapping collapsible SPTEs, rather than freezing them first. Freezing the SPTE first is not required. It is fine for another thread holding mmu_lock for read to immediately install a present entry before TLBs are flushed because the underlying mapping is not changing. vCPUs that translate through the stale 4K mappings or a new huge page mapping will still observe the same GPA->HPA translations. KVM must only flush TLBs before dropping RCU (to avoid use-after-free of the zapped page tables) and before dropping mmu_lock (to synchronize with mmu_notifiers invalidating mappings). In VMs backed with 2MiB pages, batching TLB flushes improves the time it takes to zap collapsible SPTEs to disable dirty logging: $ ./dirty_log_perf_test -s anonymous_hugetlb_2mb -v 64 -e -b 4g Before: Disabling dirty logging time: 14.334453428s (131072 flushes) After: Disabling dirty logging time: 4.794969689s (76 flushes) Skipping freezing SPTEs also avoids stalling vCPU threads on the frozen SPTE for the time it takes to perform a remote TLB flush. vCPUs faulting on the zapped mapping can now immediately install a new huge mapping and proceed with guest execution. Signed-off-by: David Matlack <dmatlack@google.com> Link: https://lore.kernel.org/r/20240823235648.3236880-3-dmatlack@google.com Signed-off-by: Sean Christopherson <seanjc@google.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 reStructuredText 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.