On Mon, Nov 27, 2017 at 12:14:08AM +0100, Thomas Gleixner wrote: > KAISER comes with overhead. The most expensive part is the CR3 switching in > the entry code. > > Add a command line parameter which allows to disable KAISER at boot time. > > Most code pathes simply check a variable, but the entry code uses a static > branch. The other code pathes cannot use a static branch because they are > used before jump label patching is possible. Not an issue as the code > pathes are not so performance sensitive as the entry/exit code. > > This makes KAISER depend on JUMP_LABEL and on a GCC which supports > it, but that's a resonable requirement. > > The PGD allocation is still 8k when CONFIG_KAISER is enabled. This can be > addressed on top of this.
So in patch 15 Andy notes that we should probably also disable the SYSCALL trampoline when we disable KAISER. https://lkml.kernel.org/r/[email protected]
