On Fri, Nov 24, 2017 at 10:14:35AM +0100, Ingo Molnar wrote: > From: Dave Hansen <dave.han...@linux.intel.com> > > There is some rather arcane code to help when an IRET returns > to 16-bit segments. It is referred to as the "espfix" code. > This consists of a few per-cpu variables: > > espfix_stack: tells us where the stack is allocated > (the bottom) > espfix_waddr: tells us to where %rsp may be pointed > (the top) > > These are in addition to the stack itself. All three things must > be mapped for the espfix code to function. > > Note: the espfix code runs with a kernel GSBASE, but user > (shadow) page tables. A switch to the kernel page tables could > be performed instead of mapping these structures, but mapping > them is simpler and less likely to break the assembly. To switch > over to the kernel copy, additional temporary storage would be > required which is in short supply in this context.
With Andy's patches that should actually be doable, no?
