Re: [PATCH 1/5] x86/mm/kaiser: Alternative ESPFIX

[Dave Hansen]

On 11/27/2017 02:31 PM, Peter Zijlstra wrote:
> Change the asm to do the CR3 switcheroo so we can remove the magic
> mappings.
> 
> Since RDI is unused after SWAPGS we can use it as a scratch reg for
> SWITCH_TO_KERNEL. And once we've computed the new RSP (in RAX) we no
> longer need RDI and can again use it as scratch reg for
> SWITCH_TO_USER.

This definitely looks like the right thing.  Either I missed something
obvious before, or Andy's entry rework made this much more obviously
correct to do the simple thing here.