On 19 May 2014 14:58, Marc Zyngier <marc.zyngier@xxxxxxx> wrote: > On Mon, May 19 2014 at 10:05:42 am BST, Anup Patel <anup.patel@xxxxxxxxxx> wrote > > Hi Anup, > >> Overall the patchset looks good to me. >> >> The debug register usage by Guest will be very rare >> so a lazy save/restore makes lot-of-sense here. >> >> The only concern here is that amount of time spend in >> world-switch will increase for Guest once Guest starts >> accessing debug registers. >> >> I was wondering if it is possible to detect that Guest >> has stopped using debug HW and we can mark debug >> state as clean. (or something similar) > > If you look carefully at patch #8 (last hunk of the patch), you'll see > that I always reset the debug state to "clean" at the end of a guest > run: > > @@ -609,6 +1040,12 @@ __kvm_vcpu_return: > > bl __restore_sysregs > bl __restore_fpsimd > + > + skip_clean_debug_state x3, 1f > + // Clear the dirty flag for the next run > + str xzr, [x0, #VCPU_DEBUG_FLAGS] > + bl __restore_debug > +1: > restore_host_regs > > mov x0, x1 > > This ensures that the guest's debug state will only be reloaded if: > > - MDSCR_EL1 has either MDE or KDE set (which means the guest is actively > using the debug infrastructure) > - or the guest has written to a trapped register (which marks the state > as dirty). Thanks for pointing out. Can you add this info as comment in patch#8 where you clear the dirty flag? > > I don't think we can do less work than this. Or can we? > > Thanks, > > M. > -- > Jazz is not dead. It just smells funny. -- Anup -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
