linux-kernel - Re: [PATCH v5 01/23] irqchip/gic-v3: Use SGIs without active state if offered

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Date:   Fri, 13 Mar 2020 09:39:08 +0800
From:   Zenghui Yu <yuzenghui@...wei.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <kvmarm@...ts.cs.columbia.edu>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jason Cooper <jason@...edaemon.net>,
        "Robert Richter" <rrichter@...vell.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Eric Auger" <eric.auger@...hat.com>,
        James Morse <james.morse@....com>,
        "Julien Thierry" <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>
Subject: Re: [PATCH v5 01/23] irqchip/gic-v3: Use SGIs without active state if
 offered

Hi Marc,

On 2020/3/12 20:05, Marc Zyngier wrote:
> On 2020-03-12 09:28, Marc Zyngier wrote:
>> Hi Zenghui,
>>
>> On 2020-03-12 06:30, Zenghui Yu wrote:
>>> Hi Marc,
>>>
>>> On 2020/3/5 4:33, Marc Zyngier wrote:
>>>> To allow the direct injection of SGIs into a guest, the GICv4.1
>>>> architecture has to sacrifice the Active state so that SGIs look
>>>> a lot like LPIs (they are injected by the same mechanism).
>>>>
>>>> In order not to break existing software, the architecture gives
>>>> offers guests OSs the choice: SGIs with or without an active
>>>> state. It is the hypervisors duty to honor the guest's choice.
>>>>
>>>> For this, the architecture offers a discovery bit indicating whether
>>>> the GIC supports GICv4.1 SGIs (GICD_TYPER2.nASSGIcap), and another
>>>> bit indicating whether the guest wants Active-less SGIs or not
>>>> (controlled by GICD_CTLR.nASSGIreq).
>>>
>>> I still can't find the description of these two bits in IHI0069F.
>>> Are they actually architected and will be available in the future
>>> version of the spec?  I want to confirm it again since this has a
>>> great impact on the KVM code, any pointers?
>>
>> Damn. The bits *are* in the engineering spec version 19 (unfortunately
>> not a public document, but I believe you should have access to it).
>>
>> If the bits have effectively been removed from the spec, I'll drop the
>> GICv4.1 code from the 5.7 queue until we find a way to achieve the same
>> level of support.
>>
>> I've emailed people inside ARM to find out.
> 
> I've now had written confirmation that the bits are still there.
> 
> It is just that the current revision of the documentation was cut *before*
> they made it into the architecture (there seem to be a 6 month delay 
> between
> the architecture being sampled and the documentation being released).

I see. Thanks for the confirmation!


Zenghui