Re: [PATCH v4] xen/arm: Allow QEMU platform to be built with GICv2

[Julien Grall <julien@xxxxxxx>]

Hi,

On 19/01/2022 15:30, Dongjiu Geng wrote:
> Bertrand Marquis <Bertrand.Marquis@xxxxxxx> 于2022年1月18日周二 17:17写道：
> > Hi Dongju,
> >
> > > On 18 Jan 2022, at 08:58, Dongjiu Geng <gengdongjiu1@xxxxxxxxx> wrote:
> > >
> > > Bertrand Marquis <Bertrand.Marquis@xxxxxxx> 于2022年1月18日周二 16:48写道：
> > > > Hi Dongju,
> > > >
> > > > > On 18 Jan 2022, at 08:45, Dongjiu Geng <gengdongjiu1@xxxxxxxxx> wrote:
> > > > >
> > > > > Julien Grall <julien@xxxxxxx> 于2022年1月17日周一 22:16写道：
> > > > > > Hi,
> > > > > >
> > > > > > On 17/01/2022 10:40, Dongjiu Geng wrote:
> > > > > > > It turns out that QEMU has been supporting GICv2 virtualization since
> > > > > > > v3.1.0. So remove the dependencies on GICv3.
> > > > > >
> > > > > > Technically, the current form of CONFIG_QEMU allows the same binary to
> > > > > > boot on QEMU with GICv2 or GICv3.
> > > > > >
> > > > > > > If we want to use GICv3,
> > > > > > > we can select the QEMU_LEGACY configuration.
> > > > > > AFAIK, GICv3 is not a legacy feature... So it feels a bit odd to name it
> > > > > > like that (see more below).
> > > > > Legacy means QEMU platform only supports GICV3, now it can support
> > > > > both GICv2 and GICv3. The scope of support has been expanded
> > > > > Not mean GICv3 is a legacy feature.
> > > > You might be misleading a bit here.
> > > > In the current configuration, Xen support GICv2, GICv3 and vgic.
> > > > The only thing not supported is actually the new VGIC but this is an 
> > > > unsupported feature not fully functional which shall be used with caution.
> > > >
> > > > What issue exactly do you have in Qemu configured for gicv2 when you use the 
> > > > default configuration ?
> > > I want to use NEW_VGIC with GICv2, but QEMU only select GICV3,  when
> > > GICv3 is select, the NEW_VGIC can not be used.   I try the NEW_VGIC
> > > with GICv2, not found issue. so I want to remove this limitation.
> > > If  you think we should not support NEW_VGIC feature,  we can ignore
> > > this patch.  thanks!
> > Supporting GICv2 makes sense but using NEW_VGIC in Xen might not as it is not 
> > security supported and does not support ITS and MSIs.
>     It is surely that NEW_VGIC not support ITS and MSI.  but I think
> QEMU platform should not limit user select it.
The goal of the option CONFIG_<platform> is to select the minimal set of 
CONFIG_* to allow booting on a given platform. Given that QEMU is 
supporting both GICv2 and GICv3, then I think it is correct to select 
both options.
>  Selecting GICv2、GICv3
> or NEW_VGIC may be chosen by users. But I find user can select it at
> all.
>
> > Do you have a reason to use the NEW_VGIC implementation instead of the standard 
> > one ?
> I add some features which is ported from KVM,  NEW_VGIC is refereed to
> KVM，so it easily integrate
Ok. So why does this needs to be done with CONFIG_QEMU? Can't you use 
defconfig + select the NEW_VGIC by hand?
Cheers,

--
Julien Grall