[PATCH 0/9] arm64: KVM: debug infrastructure support
anup.patel at linaro.org
Mon May 19 02:35:58 PDT 2014
On 19 May 2014 14:58, Marc Zyngier <marc.zyngier at arm.com> wrote:
> On Mon, May 19 2014 at 10:05:42 am BST, Anup Patel <anup.patel at linaro.org> 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
> @@ -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
> 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?
> Jazz is not dead. It just smells funny.
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