On Mon, May 19 2014 at 10:35:58 am BST, Anup Patel <anup.patel@xxxxxxxxxx> wrote: > 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? Right. There is already some comments to that effect just above, where we compute the dirty state, but I think it doesn't hurt to repeat it. Thanks, M. -- Jazz is not dead. It just smells funny. -- 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
