[libvirt PATCH 0/3] Invalidate the cpu flags cache on changes of kernel command line

Daniel P. Berrangé berrange at redhat.com
Thu Aug 5 13:50:51 UTC 2021

On Thu, Aug 05, 2021 at 03:36:37PM +0200, Tim Wiederhake wrote:
> The kernel command line can contain settings affecting the availability
> of cpu features, eg. "tsx=on". This series adds the kernel command line
> to the cpu flags cache and declares the cache invalid if the current
> kernel command line differs.

Multiple things can change the CPU features. kernel version,
microcode version, bios settings change, kernel command line. We've
been playing whack-a-mole in cache invalidation for ages adding ever
more criteria for things which have side effects on CPU features

Running the CPUID instruction is cheap. Could we directly query the
set of host CPUID leaves we care about, and compare that, and
potentially even get rid of some of the other checks we have ?

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