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Retry the optimized APIC map recalculation if an APIC-enabled vCPU shows up between allocating the map and filling in the map data. Conditionally reschedule before retrying even though the number of vCPUs that can be created is bounded by KVM. Retrying a few thousand times isn't so slow as to be hugely problematic, but it's not blazing fast either. Reset xapic_id_mistach on each retry as a vCPU could change its xAPIC ID between loops, but do NOT reset max_id. The map size also factors in whether or not a vCPU's local APIC is hardware-enabled, i.e. userspace and/or the guest can theoretically keep KVM retrying indefinitely. The only downside is that KVM will allocate more memory than is strictly necessary if the vCPU with the highest x2APIC ID disabled its APIC while the recalculation was in-progress. Refresh kvm->arch.apic_map_dirty to opportunistically change it from DIRTY => UPDATE_IN_PROGRESS to avoid an unnecessary recalc from a different task, i.e. if another task is waiting to attempt an update (which is likely since a retry happens if and only if an update is required). Link: https://lore.kernel.org/r/20230602233250.1014316-3-seanjc@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 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.