From: Marc Zyngier <marc.zyngier@arm.com>
To: Christoffer Dall <christoffer.dall@linaro.org>
Cc: kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
Andre Przywara <andre.przywara@arm.com>,
Eric Auger <eric.auger@redhat.com>
Subject: Re: [PATCH v8 3/9] KVM: arm/arm64: Don't cache the timer IRQ level
Date: Wed, 13 Dec 2017 19:38:44 +0000 [thread overview]
Message-ID: <86indawh8b.wl-marc.zyngier@arm.com> (raw)
In-Reply-To: <20171213104602.16383-4-christoffer.dall@linaro.org>
On Wed, 13 Dec 2017 10:45:56 +0000,
Christoffer Dall wrote:
>
> The timer was modeled after a strict idea of modelling an interrupt line
> level in software, meaning that only transitions in the level needed to
> be reported to the VGIC. This works well for the timer, because the
> arch timer code is in complete control of the device and can track the
> transitions of the line.
>
> However, as we are about to support using the HW bit in the VGIC not
> just for the timer, but also for VFIO which cannot track transitions of
> the interrupt line, we have to decide on an interface for level
> triggered mapped interrupts to the GIC, which both the timer and VFIO
> can use.
>
> VFIO only sees an asserting transition of the physical interrupt line,
> and tells the VGIC when that happens. That means that part of the
> interrupt flow is offloaded to the hardware.
>
> To use the same interface for VFIO devices and the timer, we therefore
> have to change the timer (we cannot change VFIO because it doesn't know
> the details of the device it is assigning to a VM).
>
> Luckily, changing the timer is simple, we just need to stop 'caching'
> the line level, but instead let the VGIC know the state of the timer
> every time there is a potential change in the line level, and when the
> line level should be asserted from the timer ISR. The VGIC can ignore
> extra notifications using its validate mechanism.
>
> Reviewed-by: Andre Przywara <andre.przywara@arm.com>
> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
M.
WARNING: multiple messages have this Message-ID (diff)
From: marc.zyngier@arm.com (Marc Zyngier)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v8 3/9] KVM: arm/arm64: Don't cache the timer IRQ level
Date: Wed, 13 Dec 2017 19:38:44 +0000 [thread overview]
Message-ID: <86indawh8b.wl-marc.zyngier@arm.com> (raw)
In-Reply-To: <20171213104602.16383-4-christoffer.dall@linaro.org>
On Wed, 13 Dec 2017 10:45:56 +0000,
Christoffer Dall wrote:
>
> The timer was modeled after a strict idea of modelling an interrupt line
> level in software, meaning that only transitions in the level needed to
> be reported to the VGIC. This works well for the timer, because the
> arch timer code is in complete control of the device and can track the
> transitions of the line.
>
> However, as we are about to support using the HW bit in the VGIC not
> just for the timer, but also for VFIO which cannot track transitions of
> the interrupt line, we have to decide on an interface for level
> triggered mapped interrupts to the GIC, which both the timer and VFIO
> can use.
>
> VFIO only sees an asserting transition of the physical interrupt line,
> and tells the VGIC when that happens. That means that part of the
> interrupt flow is offloaded to the hardware.
>
> To use the same interface for VFIO devices and the timer, we therefore
> have to change the timer (we cannot change VFIO because it doesn't know
> the details of the device it is assigning to a VM).
>
> Luckily, changing the timer is simple, we just need to stop 'caching'
> the line level, but instead let the VGIC know the state of the timer
> every time there is a potential change in the line level, and when the
> line level should be asserted from the timer ISR. The VGIC can ignore
> extra notifications using its validate mechanism.
>
> Reviewed-by: Andre Przywara <andre.przywara@arm.com>
> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
M.
next prev parent reply other threads:[~2017-12-13 19:38 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-13 10:45 [PATCH v8 0/9] Handle forwarded level-triggered interrupts Christoffer Dall
2017-12-13 10:45 ` Christoffer Dall
2017-12-13 10:45 ` [PATCH v8 1/9] KVM: arm/arm64: Remove redundant preemptible checks Christoffer Dall
2017-12-13 10:45 ` Christoffer Dall
2017-12-13 10:45 ` [PATCH v8 2/9] KVM: arm/arm64: Factor out functionality to get vgic mmio requester_vcpu Christoffer Dall
2017-12-13 10:45 ` Christoffer Dall
2017-12-13 10:45 ` [PATCH v8 3/9] KVM: arm/arm64: Don't cache the timer IRQ level Christoffer Dall
2017-12-13 10:45 ` Christoffer Dall
2017-12-13 19:38 ` Marc Zyngier [this message]
2017-12-13 19:38 ` Marc Zyngier
2017-12-19 14:17 ` Julien Thierry
2017-12-19 14:17 ` Julien Thierry
2017-12-19 20:35 ` Christoffer Dall
2017-12-19 20:35 ` Christoffer Dall
2017-12-13 10:45 ` [PATCH v8 4/9] KVM: arm/arm64: vgic: Support level-triggered mapped interrupts Christoffer Dall
2017-12-13 10:45 ` Christoffer Dall
2017-12-13 10:45 ` [PATCH v8 5/9] KVM: arm/arm64: Support a vgic interrupt line level sample function Christoffer Dall
2017-12-13 10:45 ` Christoffer Dall
2017-12-13 10:45 ` [PATCH v8 6/9] KVM: arm/arm64: Support VGIC dist pend/active changes for mapped IRQs Christoffer Dall
2017-12-13 10:45 ` Christoffer Dall
2017-12-13 10:46 ` [PATCH v8 7/9] KVM: arm/arm64: Provide a get_input_level for the arch timer Christoffer Dall
2017-12-13 10:46 ` Christoffer Dall
2017-12-13 19:45 ` Marc Zyngier
2017-12-13 19:45 ` Marc Zyngier
2017-12-13 10:46 ` [PATCH v8 8/9] KVM: arm/arm64: Avoid work when userspace iqchips are not used Christoffer Dall
2017-12-13 10:46 ` Christoffer Dall
2017-12-13 20:05 ` Marc Zyngier
2017-12-13 20:05 ` Marc Zyngier
2017-12-19 13:34 ` Christoffer Dall
2017-12-19 13:34 ` Christoffer Dall
2017-12-19 13:55 ` Marc Zyngier
2017-12-19 13:55 ` Marc Zyngier
2017-12-19 14:18 ` Christoffer Dall
2017-12-19 14:18 ` Christoffer Dall
2017-12-19 14:32 ` Marc Zyngier
2017-12-19 14:32 ` Marc Zyngier
2017-12-13 10:46 ` [PATCH v8 9/9] KVM: arm/arm64: Update timer and forwarded irq documentation Christoffer Dall
2017-12-13 10:46 ` Christoffer Dall
2017-12-13 20:15 ` Marc Zyngier
2017-12-13 20:15 ` Marc Zyngier
2017-12-19 20:29 ` Christoffer Dall
2017-12-19 20:29 ` Christoffer Dall
2017-12-19 20:35 ` Marc Zyngier
2017-12-19 20:35 ` Marc Zyngier
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