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From: Christoffer Dall <cdall@linaro.org>
To: Andrew Jones <drjones@redhat.com>
Cc: kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org,
	Marc Zyngier <marc.zyngier@arm.com>,
	Eric Auger <eric.auger@redhat.com>,
	kvm@vger.kernel.org, Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH v5 19/20] KVM: arm/arm64: Get rid of kvm_timer_flush_hwstate
Date: Wed, 29 Nov 2017 18:39:00 +0100	[thread overview]
Message-ID: <20171129173900.GE10563@lvm> (raw)
In-Reply-To: <20171127165012.2egz3dos6h4zj7ub@kamzik.brq.redhat.com>

On Mon, Nov 27, 2017 at 05:50:12PM +0100, Andrew Jones wrote:
> On Fri, Oct 27, 2017 at 10:34:40AM +0200, Christoffer Dall wrote:
> > diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> > index 132d39a..14c50d1 100644
> > --- a/virt/kvm/arm/arm.c
> > +++ b/virt/kvm/arm/arm.c
> > @@ -656,7 +656,6 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> >  
> >  		local_irq_disable();
> >  
> > -		kvm_timer_flush_hwstate(vcpu);
> >  		kvm_vgic_flush_hwstate(vcpu);
> >  
> >  		/*
> > -- 
> > 2.7.4
> 
> Hi Christoffer,
> 
> I realize this is already merged, but I have a question about the
> above hunk. IIUC, the patch "KVM: arm/arm64: Move timer/vgic
> flush/sync under disabled irq" only moved kvm_vgic_flush_hwstate()
> under disabled irq because it had to be run after
> kvm_timer_flush_hwstate(). Now that kvm_timer_flush_hwstate() is
> gone can/should it be moved back out?
> 

That's a great question.

I think my reasoning was, that since we now disable the VCPU interface
(and thereby maintenance interrupts), any logic that relies on a
maintenance interrupt firing and causing a guest exit after we've called
flush, would no longer work if we move this back out where interrupts
are enabled.

Thinking about this a bit more, I don't think that would ever make
sense, and we should be able to move it out.

I've tested these patches pretty heavily and would want such a change to
get the same kind of exposure, so I can start testing it, and if there
are no issues, put it in next later on in the cycle.

Does that sound reasonable?

Thanks,
-Christoffer

WARNING: multiple messages have this Message-ID (diff)
From: cdall@linaro.org (Christoffer Dall)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v5 19/20] KVM: arm/arm64: Get rid of kvm_timer_flush_hwstate
Date: Wed, 29 Nov 2017 18:39:00 +0100	[thread overview]
Message-ID: <20171129173900.GE10563@lvm> (raw)
In-Reply-To: <20171127165012.2egz3dos6h4zj7ub@kamzik.brq.redhat.com>

On Mon, Nov 27, 2017 at 05:50:12PM +0100, Andrew Jones wrote:
> On Fri, Oct 27, 2017 at 10:34:40AM +0200, Christoffer Dall wrote:
> > diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> > index 132d39a..14c50d1 100644
> > --- a/virt/kvm/arm/arm.c
> > +++ b/virt/kvm/arm/arm.c
> > @@ -656,7 +656,6 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> >  
> >  		local_irq_disable();
> >  
> > -		kvm_timer_flush_hwstate(vcpu);
> >  		kvm_vgic_flush_hwstate(vcpu);
> >  
> >  		/*
> > -- 
> > 2.7.4
> 
> Hi Christoffer,
> 
> I realize this is already merged, but I have a question about the
> above hunk. IIUC, the patch "KVM: arm/arm64: Move timer/vgic
> flush/sync under disabled irq" only moved kvm_vgic_flush_hwstate()
> under disabled irq because it had to be run after
> kvm_timer_flush_hwstate(). Now that kvm_timer_flush_hwstate() is
> gone can/should it be moved back out?
> 

That's a great question.

I think my reasoning was, that since we now disable the VCPU interface
(and thereby maintenance interrupts), any logic that relies on a
maintenance interrupt firing and causing a guest exit after we've called
flush, would no longer work if we move this back out where interrupts
are enabled.

Thinking about this a bit more, I don't think that would ever make
sense, and we should be able to move it out.

I've tested these patches pretty heavily and would want such a change to
get the same kind of exposure, so I can start testing it, and if there
are no issues, put it in next later on in the cycle.

Does that sound reasonable?

Thanks,
-Christoffer

  reply	other threads:[~2017-11-29 17:39 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-27  8:34 [PATCH v5 00/20] KVM: arm/arm64: Optimize arch timer register handling Christoffer Dall
2017-10-27  8:34 ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 01/20] irqchip/gic: Deal with broken firmware exposing only 4kB of GICv2 CPU interface Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 02/20] arm64: Implement arch_counter_get_cntpct to read the physical counter Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27 10:53   ` Catalin Marinas
2017-10-27 10:53     ` Catalin Marinas
2017-10-29  1:51     ` Christoffer Dall
2017-10-29  1:51       ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 03/20] arm64: Use physical counter for in-kernel reads when booted in EL2 Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27 10:53   ` Catalin Marinas
2017-10-27 10:53     ` Catalin Marinas
2017-10-27  8:34 ` [PATCH v5 04/20] KVM: arm/arm64: Guard kvm_vgic_map_is_active against !vgic_initialized Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-11-16 12:29   ` Andre Przywara
2017-11-16 12:29     ` Andre Przywara
2017-11-20 11:20     ` Christoffer Dall
2017-11-20 11:20       ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 05/20] KVM: arm/arm64: Support calling vgic_update_irq_pending from irq context Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 06/20] KVM: arm/arm64: Check that system supports split eoi/deactivate Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 07/20] KVM: arm/arm64: Make timer_arm and timer_disarm helpers more generic Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 08/20] KVM: arm/arm64: Rename soft timer to bg_timer Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 09/20] KVM: arm/arm64: Move timer/vgic flush/sync under disabled irq Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 10/20] KVM: arm/arm64: Use separate timer for phys timer emulation Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 11/20] KVM: arm/arm64: Move timer save/restore out of the hyp code Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 12/20] genirq: Document vcpu_info usage for percpu_devid interrupts Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-29 15:22   ` [tip:irq/core] " tip-bot for Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 13/20] KVM: arm/arm64: Set VCPU affinity for virt timer irq Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 14/20] KVM: arm/arm64: Avoid timer save/restore in vcpu entry/exit Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 15/20] KVM: arm/arm64: Support EL1 phys timer register access in set/get reg Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 16/20] KVM: arm/arm64: Use kvm_arm_timer_set/get_reg for guest register traps Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 17/20] KVM: arm/arm64: Move phys_timer_emulate function Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 18/20] KVM: arm/arm64: Avoid phys timer emulation in vcpu entry/exit Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-27  8:34 ` [PATCH v5 19/20] KVM: arm/arm64: Get rid of kvm_timer_flush_hwstate Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-11-27 16:50   ` Andrew Jones
2017-11-27 16:50     ` Andrew Jones
2017-11-29 17:39     ` Christoffer Dall [this message]
2017-11-29 17:39       ` Christoffer Dall
2017-11-29 18:17       ` Andrew Jones
2017-11-29 18:17         ` Andrew Jones
2017-10-27  8:34 ` [PATCH v5 20/20] KVM: arm/arm64: Rework kvm_timer_should_fire Christoffer Dall
2017-10-27  8:34   ` Christoffer Dall
2017-10-29  1:48 ` [PATCH v5 21/20] arm/arm64: KVM: Load the timer state when enabling the timer Christoffer Dall
2017-10-29  1:48   ` Christoffer Dall
2017-10-29  2:07   ` Marc Zyngier
2017-10-29  2:07     ` Marc Zyngier

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