Re: [PATCH v6 8/9] KVM: arm/arm64: Document KVM_DEV_ARM_ITS_CTRL_RESET

Marc Zyngier
2017-10-30T03:20:28Z

On Thu, Oct 26 2017 at 6:23:10 pm BST, Eric Auger <eric.auger@redhat.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@redhat.com>
> Reported-by: wanghaibin <wanghaibin.wang@huawei.com>

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

M.
--
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