Hi Andy, On Mon, Apr 27, 2020 at 10:37:41AM -0700, Andy Lutomirski wrote: > 1. Use IST for #VC and deal with all the mess that entails.
With the removal of IST shifting I wonder what you would suggest on how to best implement an NMI-safe IST handler with nesting support. My current plan is to implement an IST handler which switches itself off the IST stack as soon as possible, freeing it for re-use. The flow would be roughly like this upon entering the handler; build_pt_regs(); RSP = pt_regs->sp; if (RSP in VC_IST_stack) error("unallowed nesting") if (RSP in current_kernel_stack) RSP = round_down_to_8(RSP) else RSP = current_top_of_stack() // non-ist kernel stack copy_pt_regs(pt_regs, RSP); switch_stack_to(RSP); To make this NMI safe, the NMI handler needs some logic too. Upon entering NMI, it needs to check the return RSP, and if it is in the #VC IST stack, it must do the above flow by itself and update the return RSP and RIP. It needs to take into account the case when PT_REGS is not fully populated on the return side. Alternativly the NMI handler could safe/restore the contents of the #VC IST stack or just switch to a special #VC-in-NMI IST stack. All in all it could get complicated, and imho shift_ist would have been simpler, but who am I anyway... Or maybe you have a better idea how to implement this, so I'd like to hear your opinion first before I spend too many days implementing something. Regards, Joerg _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization