On 14/01/13 22:08, Christoffer Dall wrote: > On Mon, Jan 14, 2013 at 12:51 PM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote: >> On 14/01/13 15:21, Will Deacon wrote: >>> On Tue, Jan 08, 2013 at 06:43:27PM +0000, Christoffer Dall wrote: >>>> From: Marc Zyngier <marc.zyngier@xxxxxxx> >>>> >>>> Do the necessary save/restore dance for the timers in the world >>>> switch code. In the process, allow the guest to read the physical >>>> counter, which is useful for its own clock_event_device. >>> >>> [...] >>> >>>> @@ -476,6 +513,7 @@ vcpu .req r0 @ vcpu pointer always in r0 >>>> * for the host. >>>> * >>>> * Assumes vcpu pointer in vcpu reg >>>> + * Clobbers r2-r4 >>>> */ >>>> .macro restore_timer_state >>>> @ Disallow physical timer access for the guest >>>> @@ -484,6 +522,30 @@ vcpu .req r0 @ vcpu pointer always in r0 >>>> orr r2, r2, #CNTHCTL_PL1PCTEN >>>> bic r2, r2, #CNTHCTL_PL1PCEN >>>> mcr p15, 4, r2, c14, c1, 0 @ CNTHCTL >>>> + >>>> +#ifdef CONFIG_KVM_ARM_TIMER >>>> + ldr r4, [vcpu, #VCPU_KVM] >>>> + ldr r2, [r4, #KVM_TIMER_ENABLED] >>>> + cmp r2, #0 >>>> + beq 1f >>>> + >>>> + ldr r2, [r4, #KVM_TIMER_CNTVOFF] >>>> + ldr r3, [r4, #(KVM_TIMER_CNTVOFF + 4)] >>>> + mcrr p15, 4, r2, r3, c14 @ CNTVOFF >>>> + isb >>>> + >>>> + ldr r4, =VCPU_TIMER_CNTV_CVAL >>>> + add vcpu, vcpu, r4 >>>> + ldrd r2, r3, [vcpu] >>>> + sub vcpu, vcpu, r4 >>>> + mcrr p15, 3, r2, r3, c14 @ CNTV_CVAL >>>> + >>>> + ldr r2, [vcpu, #VCPU_TIMER_CNTV_CTL] >>>> + and r2, r2, #3 >>>> + mcr p15, 0, r2, c14, c3, 1 @ CNTV_CTL >>>> + isb >>> >>> How many of these isbs are actually needed, given that we're going to make >>> an exception return to the guest? The last one certainly looks redundant and >>> I can't see the need for ordering CNTVOFF vs CNTV_CVAL. I can see an >>> argument to putting one *before* CNTV_CTL, but you don't have one there! >> >> CNTVOFF directly influences whether or not CNTV_CVAL will trigger or >> not. Maybe I'm just being paranoid and moving the isb after CNTV_CVAL is >> enough. >> >> The last one is definitively superfluous. >> > > can't we also get rid of the isb on the return path then? > > do you agree with this patch: > > diff --git a/arch/arm/kvm/interrupts_head.S b/arch/arm/kvm/interrupts_head.S > index 57cfa84..7e6eedf 100644 > --- a/arch/arm/kvm/interrupts_head.S > +++ b/arch/arm/kvm/interrupts_head.S > @@ -492,7 +492,6 @@ vcpu .req r0 @ vcpu pointer always in r0 > str r2, [vcpu, #VCPU_TIMER_CNTV_CTL] > bic r2, #1 @ Clear ENABLE > mcr p15, 0, r2, c14, c3, 1 @ CNTV_CTL > - isb This isb is required. Otherwise you have no guarantee about how recent the next CNTV_CVAL read is (could be speculated). > mrrc p15, 3, r2, r3, c14 @ CNTV_CVAL > ldr r4, =VCPU_TIMER_CNTV_CVAL > @@ -532,18 +531,17 @@ vcpu .req r0 @ vcpu pointer always in r0 > ldr r2, [r4, #KVM_TIMER_CNTVOFF] > ldr r3, [r4, #(KVM_TIMER_CNTVOFF + 4)] > mcrr p15, 4, r2, r3, c14 @ CNTVOFF > - isb > > ldr r4, =VCPU_TIMER_CNTV_CVAL > add vcpu, vcpu, r4 > ldrd r2, r3, [vcpu] > sub vcpu, vcpu, r4 > mcrr p15, 3, r2, r3, c14 @ CNTV_CVAL > + isb > > ldr r2, [vcpu, #VCPU_TIMER_CNTV_CTL] > and r2, r2, #3 > mcr p15, 0, r2, c14, c3, 1 @ CNTV_CTL > - isb > 1: > #endif > .endm This part is OK. 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
