> So on user space to kernel space transitions swapping in kernel GS should > simply do: > userGS = RDGSBASE() > WRGSBASE(kernelGS)
This would also need to find kernelGS first, by doing RDPID and then reading it from memory in the right index (which might be a full cache miss if you're unlucky) SWAPGS will be a lot faster, especially in these rare worst cases because it has all its state inside the CPU. -Andi BTW you managed to only review after Chang went on a long vacation. <rant> I don't understand why it takes that long to review these changes It's one of the largest performance improvements for the context switch and the NMI in many years plus gives a new free register to user space, but it only makes progress at a glacial pace. The original patches for this were posted in 2016. </rant>
