From: Borislav Petkov<borislav.petkov@xxxxxxx>
This patch provides performance tuning for the "Bulldozer" CPU. With its
shared instruction cache there is a chance of generating an excessive
number of cache cross-invalidates when running specific workloads on the
cores of a compute module.
This excessive amount of cross-invalidations can be observed if cache
lines backed by shared physical memory alias in bits [14:12] of their
virtual addresses, as those bits are used for the index generation.
This patch addresses the issue by zeroing out the slice [14:12] of
the file mapping's virtual address at generation time, thus forcing
those bits the same for all mappings of a single shared library across
processes and, in doing so, avoids instruction cache aliases.
It also adds the kernel command line option
"unalias_va_addr=(32|64|off)" with which virtual address unaliasing
can be enabled for 32-bit or 64-bit x86 individually, or be completely
disabled.
This change leaves virtual region address allocation on other families
and/or vendors unaffected.