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From: marc.zyngier@arm•com (Marc Zyngier)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 0/9] arm64: KVM: debug infrastructure support
Date: Mon, 19 May 2014 10:28:32 +0100	[thread overview]
Message-ID: <87d2fanmm7.fsf@approximate.cambridge.arm.com> (raw)
In-Reply-To: <CALrVBkscsWxRsS42eJi9deFeaBbjQMKq9R2e-u5ztu70rKUvUw@mail.gmail.com> (Anup Patel's message of "Mon, 19 May 2014 10:05:42 +0100")

On Mon, May 19 2014 at 10:05:42 am BST, Anup Patel <anup.patel@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
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).

I don't think we can do less work than this. Or can we?

Thanks,

        M.
-- 
Jazz is not dead. It just smells funny.

next prev parent reply	other threads:[~2014-05-19  9:28 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-05-07 15:20 [PATCH 0/9] arm64: KVM: debug infrastructure support Marc Zyngier
2014-05-07 15:20 ` [PATCH 1/9] arm64: KVM: rename pm_fake handler to trap_wi_raz Marc Zyngier
2014-05-07 15:34   ` Peter Maydell
2014-05-07 15:42     ` Marc Zyngier
2014-05-19  8:43   ` Anup Patel
2014-05-07 15:20 ` [PATCH 2/9] arm64: move DBG_MDSCR_* to asm/debug-monitors.h Marc Zyngier
2014-05-07 17:14   ` Will Deacon
2014-05-07 15:20 ` [PATCH 3/9] arm64: KVM: add trap handlers for AArch64 debug registers Marc Zyngier
2014-05-19  8:27   ` Anup Patel
2014-05-07 15:20 ` [PATCH 4/9] arm64: KVM: common infrastructure for handling AArch32 CP14/CP15 Marc Zyngier
2014-05-19  8:29   ` Anup Patel
2014-05-07 15:20 ` [PATCH 5/9] arm64: KVM: use separate tables for AArch32 32 and 64bit traps Marc Zyngier
2014-05-19  8:29   ` Anup Patel
2014-05-07 15:20 ` [PATCH 6/9] arm64: KVM: check ordering of all system register tables Marc Zyngier
2014-05-19  8:31   ` Anup Patel
2014-05-07 15:20 ` [PATCH 7/9] arm64: KVM: add trap handlers for AArch32 debug registers Marc Zyngier
2014-05-19  8:33   ` Anup Patel
2014-05-07 15:20 ` [PATCH 8/9] arm64: KVM: implement lazy world switch for " Marc Zyngier
2014-05-19  8:38   ` Anup Patel
2014-05-19 16:01     ` Marc Zyngier
2014-05-07 15:20 ` [PATCH 9/9] arm64: KVM: enable trapping of all " Marc Zyngier
2014-05-19  8:40   ` Anup Patel
2014-05-07 15:42 ` [PATCH 0/9] arm64: KVM: debug infrastructure support Peter Maydell
2014-05-07 15:57   ` Marc Zyngier
2014-05-19  9:05 ` Anup Patel
2014-05-19  9:28   ` Marc Zyngier [this message]
2014-05-19  9:35     ` Anup Patel
2014-05-19 12:22       ` Marc Zyngier
2014-05-19 12:32     ` Peter Maydell
2014-05-19 12:59       ` Marc Zyngier

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