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The async page fault injection into kernel space creates more problems than it solves. The host has absolutely no knowledge about the state of the guest if the fault happens in CPL0. The only restriction for the host is interrupt disabled state. If interrupts are enabled in the guest then the exception can hit arbitrary code. The HALT based wait in non-preemotible code is a hacky replacement for a proper hypercall. For the ongoing work to restrict instrumentation and make the RCU idle interaction well defined the required extra work for supporting async pagefault in CPL0 is just not justified and creates complexity for a dubious benefit. The CPL3 injection is well defined and does not cause any issues as it is more or less the same as a regular page fault from CPL3. Suggested-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com> Acked-by: Paolo Bonzini <pbonzini@redhat.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Link: https://lkml.kernel.org/r/20200505134059.369802541@linutronix.de
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.