In early May, Linux creator Linus Torvalds took some time out of the big picture stuff to merge his own x86-rep-insns branch to the kernel for Linux 6.4. Torvalds explained further in the git merge: “This cleans up a lot of our x86 memory copy code, particularly for user accesses. I’ve been pushing for micro-architectural support for good memory copying and clearing for a long while.
“Micro-architectural support has been improving over the years, to the point where on modern CPUs the best option for a memory copy that would become a function call is now to inline the string instruction sequence instead. However, that only makes sense when we have the modern markers for this: the x86 FSRM and FSRS capabilities (Fast Short REP MOVS/STOS).