linux-kernel - Re: [PATCH v6 8/9] KVM: arm/arm64: Document KVM_DEV_ARM_ITS_CTRL

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Message-ID: <8660ax7226.fsf@arm.com>
Date:   Mon, 30 Oct 2017 03:21:53 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Eric Auger <eric.auger@...hat.com>
Cc:     <eric.auger.pro@...il.com>, <linux-kernel@...r.kernel.org>,
        <kvm@...r.kernel.org>, <kvmarm@...ts.cs.columbia.edu>,
        <cdall@...aro.org>, <peter.maydell@...aro.org>,
        <andre.przywara@....com>, <wanghaibin.wang@...wei.com>,
        <wu.wubin@...wei.com>, <drjones@...hat.com>, <wei@...hat.com>
Subject: Re: [PATCH v6 8/9] KVM: arm/arm64: Document KVM_DEV_ARM_ITS_CTRL_RESET

On Thu, Oct 26 2017 at  6:23:10 pm BST, Eric Auger <eric.auger@...hat.com> wrote:
> At the moment, the in-kernel emulated ITS is not properly reset.
> On guest restart/reset some registers keep their old values and
> internal structures like device, ITE, and collection lists are not
> freed.
>
> This may lead to various bugs. Among them, we can have incorrect state
> backup or failure when saving the ITS state at early guest boot stage.
>
> This patch documents a new attribute, KVM_DEV_ARM_ITS_CTRL_RESET in
> the KVM_DEV_ARM_VGIC_GRP_CTRL group.
>
> Upon this action, we can reset registers and especially those
> pointing to tables previously allocated by the guest and free
> the internal data structures storing the list of devices, collections
> and lpis.
>
> The usual approach for device reset of having userspace write
> the reset values of the registers to the kernel via the register
> read/write APIs doesn't work for the ITS because it has some
> internal state (caches) which is not exposed as registers,
> and there is no register interface for "drop cached data without
> writing it back to RAM". So we need a KVM API which mimics the
> hardware's reset line, to provide the equivalent behaviour to
> a "pull the power cord out of the back of the machine" reset.
>
> Signed-off-by: Eric Auger <eric.auger@...hat.com>
> Reported-by: wanghaibin <wanghaibin.wang@...wei.com>

Reviewed-by: Marc Zyngier <marc.zyngier@....com>

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