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

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Date:   Thu, 12 Mar 2020 12:05:05 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Zenghui Yu <yuzenghui@...wei.com>
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

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).

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