linux-kernel - Re: [RFC PATCH v1 3/4] KVM: arm64: GICv4.1: Restore VLPI's pending state to physical side

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Message-ID: <9b80d460-e149-20c8-e9b3-e695310b4ed1@huawei.com>
Date:   Tue, 1 Dec 2020 19:40:14 +0800
From:   Shenming Lu <lushenming@...wei.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Eric Auger <eric.auger@...hat.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <kvmarm@...ts.cs.columbia.edu>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Christoffer Dall <christoffer.dall@....com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Cornelia Huck <cohuck@...hat.com>, Neo Jia <cjia@...dia.com>,
        <wanghaibin.wang@...wei.com>, <yuzenghui@...wei.com>
Subject: Re: [RFC PATCH v1 3/4] KVM: arm64: GICv4.1: Restore VLPI's pending
 state to physical side

On 2020/12/1 18:55, Marc Zyngier wrote:
> On 2020-11-30 07:23, Shenming Lu wrote:
> 
> Hi Shenming,
> 
>> We are pondering over this problem these days, but still don't get a
>> good solution...
>> Could you give us some advice on this?
>>
>> Or could we move the restoring of the pending states (include the sync
>> from guest RAM and the transfer to HW) to the GIC VM state change handler,
>> which is completely corresponding to save_pending_tables (more symmetric?)
>> and don't expose GICv4...
> 
> What is "the GIC VM state change handler"? Is that a QEMU thing?

Yeah, it is a a QEMU thing...

> We don't really have that concept in KVM, so I'd appreciate if you could
> be a bit more explicit on this.

My thought is to add a new interface (to QEMU) for the restoring of the pending
states, which is completely corresponding to KVM_DEV_ARM_VGIC_SAVE_PENDING_TABLES...
And it is called from the GIC VM state change handler in QEMU, which is happening
after the restoring (call kvm_vgic_v4_set_forwarding()) but before the starting
(running) of the VFIO device.

Thanks,
Shenming

> 
> Thanks,
> 
>         M.