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Although in general we do not expect valid PTEs to be found in kvmppc_create_pte when we are inserting a large page mapping, there is one situation where this can occur. That is when dirty page logging is turned off for a memslot while the VM is running. Because the new memslots are installed before the old memslot is flushed in kvmppc_core_commit_memory_region_hv(), there is a window where a hypervisor page fault can try to install a 2MB (or 1GB) page where there are already small page mappings which were installed while dirty page logging was enabled and which have not yet been flushed. Since we have a situation where valid PTEs can legitimately be found by kvmppc_unmap_free_pte, and which can be triggered by userspace, just remove the WARN_ON_ONCE, since it is undesirable to have userspace able to trigger a kernel warning. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
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.