On Wed, Jan 17, 2018 at 6:10 AM, Joerg Roedel <joro@xxxxxxxxxx> wrote: > On Wed, Jan 17, 2018 at 05:57:53AM -0800, Brian Gerst wrote: >> On Wed, Jan 17, 2018 at 1:24 AM, Joerg Roedel <joro@xxxxxxxxxx> wrote: > >> > I have no real idea on how to switch back to the entry stack without >> > access to per_cpu variables. I also can't access the cpu_entry_area for >> > the cpu yet, because for that we need to be on the entry stack already. >> >> Switch to the trampoline stack before loading user segments. > > That requires to copy most of pt_regs from task- to trampoline-stack, > not sure if that is faster than temporily restoring kernel %fs. > I would optimize for simplicity, not speed. You're already planning to write to CR3, which is serializing, blows away the TLB, *and* takes the absurdly large amount of time that the microcode needs to blow away the TLB. (For whatever reason, Intel doesn't seem to have hardware that can quickly wipe the TLB. I suspect that the actual implementation does it in a loop and wipes little pieces at a time. Whatever it actually does, the CR3 write itself is very slow.) -- 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>
