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

[Dongjiu Geng <gengdongjiu1@xxxxxxxxx>]

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.  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


>
> Cheers
> Bertrand
>
> >
> >>
> >> Cheers
> >> Bertrand
> >>
> >>>
> >>>>
> >>>>>
> >>>>> Signed-off-by: Dongjiu Geng <gengdongjiu1@xxxxxxxxx>
> >>>>> ---
> >>>>> xen/arch/arm/platforms/Kconfig | 10 +++++++++-
> >>>>> 1 file changed, 9 insertions(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/xen/arch/arm/platforms/Kconfig 
> >>>>> b/xen/arch/arm/platforms/Kconfig
> >>>>> index c93a6b2756..41e82a42ee 100644
> >>>>> --- a/xen/arch/arm/platforms/Kconfig
> >>>>> +++ b/xen/arch/arm/platforms/Kconfig
> >>>>> @@ -13,7 +13,15 @@ config ALL_PLAT
> >>>>>     automatically select any of the related drivers.
> >>>>>
> >>>>> config QEMU
> >>>>> -     bool "QEMU aarch virt machine support"
> >>>>> +     bool "QEMU aarch virt machine support >= v3.1.0"
> >>>>
> >>>> This is a bit misleading. A user may select this thinking that this will
> >>>> select GICv3. However, this will not.
> >>>>
> >>>> This also raises the question of what is the default GIC version in QEMU
> >>>> (i.e. if you don't pass anything on the command line)? If this is GICv3,
> >>>> then I am afraid that this patch would be a no-go for me.
> >>>>
> >>>> Looking at overall discussion, you seem to push the patch only to allow
> >>>> building a tiny Xen for QEMU and the new vGIC.
> >>>>
> >>>> The default Xen (i.e. make defconfig) will also work on QEMU. Given that
> >>>> the new vGIC is a still in development, I am seriously considering to
> >>>> say that if you want to try it then you have to use the default
> >>>> configuration.
> >>>>
> >>>> @Dongjiu, is there any reason why you want to use the tiny QEMU config
> >>>> rather than the default configuration?
> >>>
> >>> Hi Julien, thanks for the reply, I do not use the tiny QEMU config. I
> >>> used the default configuration and selected the platform as QEMU.
> >>> But QEMU platform only slects GICV3, so I submit this patch to remove
> >>> the limitation because I want to use VGIC. VGIC can already support
> >>> GICv2 now.
> >>>
> >>>>
> >>>> @Bertrand, @Stefano, what do you think?
> >>>>
> >>>> Cheers,
> >>>>
> >>>> --
> >>>> Julien Grall
>