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Because of how the virtual clocks use U64_MAX as an exception value instead of a valid time, the clocks can no longer be assumed to wrap cleanly. This is then compounded by arch_vdso_cycles_ok() rejecting everything with the MSB/Sign-bit set. Therefore, the effective mask becomes S64_MAX, and the comment with vdso_calc_delta() that states the mask is U64_MAX and isn't optimized out is just plain silly. Now, the code has a negative filter -- to deal with TSC wobbles: if (cycles > last) which is just plain wrong, because it should've been written as: if ((s64)(cycles - last) > 0) to take wrapping into account, but per all the above, we don't actually wrap on u64 anymore. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Michael Kelley <mikelley@microsoft.com> # Hyper-V Link: https://lore.kernel.org/r/20230519102715.704767397@infradead.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.