linux-kernel - Re: [PATCH v4 02/20] irqchip/gic-v3: Use SGIs without active state if offered

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Date:   Mon, 17 Feb 2020 17:18:10 +0800
From:   Zenghui Yu <yuzenghui@...wei.com>
To:     Marc Zyngier <maz@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <kvmarm@...ts.cs.columbia.edu>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     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 v4 02/20] irqchip/gic-v3: Use SGIs without active state if
 offered

Hi Marc,

On 2020/2/14 22:57, 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).
> 
> A hypervisor not supporting GICv4.1 SGIs would leave nASSGIcap
> clear, and a guest not knowing about GICv4.1 SGIs (or definitely
> wanting an Active state) would leave nASSGIreq clear (both being
> thankfully backward compatible with oler revisions of the GIC).
older?

> 
> Since Linux is perfectly happy without an active state on SGIs,
> inform the hypervisor that we'll use that if offered.
> 
> Signed-off-by: Marc Zyngier <maz@...nel.org>

Per the description of these two bits in the commit message,

Reviewed-by: Zenghui Yu <yuzenghui@...wei.com>


Thanks