Re: [PATCHv6 07/16] x86/vsyscall: Reorganize the #PF emulation code

[Andrew Cooper]

> But, the resulting code is wonky. It needs to do something more like this:
>
> 	if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER)
> 		return false;
>
> 	if (error_code & X86_PF_INSTR))
> 		return __emulate_vsyscall(regs, address);

To do this, LASS needs a proper interlink against NX || SMEP.

If neither NX nor SMEP are active, the CPU does not report X86_PF_INSTR,
meaning that fetches are reported as plain reads.

This leads to some fun corner cases in SMAP and now LASS too for virt.

~Andrew