Hi Brian, On Mon, Mar 05, 2018 at 11:41:01AM -0500, Brian Gerst wrote: > We can keep the same process as the existing debug/NMI handlers - > leave the current exception pt_regs on the entry stack and just switch > to the task stack for the call to the handler. Then switch back to > the entry stack and continue. No copying needed. I looked into this and things are a bit more complicated than in the NMI and debug handlers. The current code after pt_regs is set up relies on %esp pointing to the pt_regs structure. But if pt_regs could be on another stack we need to carry the pt_regs pointer in another register through the whole ret_from_exception code-path until we actually switch back the stack. Since the code-path is used for all stack/cr3 entry/exit cases we need to setup the extra pt_regs pointer unconditionally and update all places that reference it through %esp. It can certainly be done but it looks like another major surgery in the entry code to optimize a slow-path for handling unlikely segment-loading exceptions and debug traps. I am not sure if it's worth it. Regards, Joerg -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
