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

[Zenghui Yu]

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@xxxxxxxxxx>

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

Reviewed-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>


Thanks