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

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

[Dongjiu Geng]

It turns out that QEMU has been supporting GICv2 virtualization since
v3.1.0. So remove the dependencies on GICv3. If we want to use GICv3,
we can select the QEMU_LEGACY configuration.

Signed-off-by: Dongjiu Geng <gengdongjiu1@gmail.com>
---
 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"
+	depends on ARM_64
+	select HAS_PL011
+	---help---
+	Enable all the required drivers for QEMU aarch64 virt emulated
+	machine.
+
+config QEMU_LEGACY
+	bool "QEMU aarch virt machine support < v3.1.0"
 	depends on ARM_64
 	select GICV3
 	select HAS_PL011
-- 
2.25.1

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

[Bertrand Marquis]

Hi,

> On 17 Jan 2022, at 06:40, Dongjiu Geng <gengdongjiu1@gmail.com> wrote:
> 
> It turns out that QEMU has been supporting GICv2 virtualization since
> v3.1.0. So remove the dependencies on GICv3. If we want to use GICv3,
> we can select the QEMU_LEGACY configuration.

I am bit puzzled by this change introducing a legacy option actually selecting the newest GIC interface.

Can’t we do the opposite and introduce a QEMU_GICV2 instead ?

Also why do we need to remove gic-v3 support ? The code should actually select which gic to use depending on the device tree.

Regards
Bertrand

> 
> Signed-off-by: Dongjiu Geng <gengdongjiu1@gmail.com>
> ---
> 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"
> +	depends on ARM_64
> +	select HAS_PL011
> +	---help---
> +	Enable all the required drivers for QEMU aarch64 virt emulated
> +	machine.
> +
> +config QEMU_LEGACY
> +	bool "QEMU aarch virt machine support < v3.1.0"
> 	depends on ARM_64
> 	select GICV3
> 	select HAS_PL011
> -- 
> 2.25.1
> 

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

[Dongjiu Geng]

Bertrand Marquis <Bertrand.Marquis@arm.com> 于2022年1月17日周一 17:00写道：
>
> Hi,
>
> > On 17 Jan 2022, at 06:40, Dongjiu Geng <gengdongjiu1@gmail.com> wrote:
> >
> > It turns out that QEMU has been supporting GICv2 virtualization since
> > v3.1.0. So remove the dependencies on GICv3. If we want to use GICv3,
> > we can select the QEMU_LEGACY configuration.
>
> I am bit puzzled by this change introducing a legacy option actually selecting the newest GIC interface.
>
> Can’t we do the opposite and introduce a QEMU_GICV2 instead ?
>
> Also why do we need to remove gic-v3 support ? The code should actually select which gic to use depending on the device tree.

QEMU platfrom only select GICv3,  so I remove this limitation,  let
user or developer selects gic version is better.

>
> Regards
> Bertrand
>
> >
> > Signed-off-by: Dongjiu Geng <gengdongjiu1@gmail.com>
> > ---
> > 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"
> > +     depends on ARM_64
> > +     select HAS_PL011
> > +     ---help---
> > +     Enable all the required drivers for QEMU aarch64 virt emulated
> > +     machine.
> > +
> > +config QEMU_LEGACY
> > +     bool "QEMU aarch virt machine support < v3.1.0"
> >       depends on ARM_64
> >       select GICV3
> >       select HAS_PL011
> > --
> > 2.25.1
> >
>

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

[Bertrand Marquis]

Hi,

> On 17 Jan 2022, at 11:12, Dongjiu Geng <gengdongjiu1@gmail.com> wrote:
> 
> Bertrand Marquis <Bertrand.Marquis@arm.com> 于2022年1月17日周一 17:00写道：
>> 
>> Hi,
>> 
>>> On 17 Jan 2022, at 06:40, Dongjiu Geng <gengdongjiu1@gmail.com> wrote:
>>> 
>>> It turns out that QEMU has been supporting GICv2 virtualization since
>>> v3.1.0. So remove the dependencies on GICv3. If we want to use GICv3,
>>> we can select the QEMU_LEGACY configuration.
>> 
>> I am bit puzzled by this change introducing a legacy option actually selecting the newest GIC interface.
>> 
>> Can’t we do the opposite and introduce a QEMU_GICV2 instead ?
>> 
>> Also why do we need to remove gic-v3 support ? The code should actually select which gic to use depending on the device tree.
> 
> QEMU platfrom only select GICv3,  so I remove this limitation,  let
> user or developer selects gic version is better.

This is where I am lost, the code is actually always compiling gic-v2 support in unless new vgic is selected (see arch/arm/Makefile).

Cheers
Bertrand

> 
>> 
>> Regards
>> Bertrand
>> 
>>> 
>>> Signed-off-by: Dongjiu Geng <gengdongjiu1@gmail.com>
>>> ---
>>> 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"
>>> +     depends on ARM_64
>>> +     select HAS_PL011
>>> +     ---help---
>>> +     Enable all the required drivers for QEMU aarch64 virt emulated
>>> +     machine.
>>> +
>>> +config QEMU_LEGACY
>>> +     bool "QEMU aarch virt machine support < v3.1.0"
>>>      depends on ARM_64
>>>      select GICV3
>>>      select HAS_PL011
>>> --
>>> 2.25.1

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

[Dongjiu Geng]

Bertrand Marquis <Bertrand.Marquis@arm.com> 于2022年1月17日周一 19:38写道：
>
> Hi,
>
> > On 17 Jan 2022, at 11:12, Dongjiu Geng <gengdongjiu1@gmail.com> wrote:
> >
> > Bertrand Marquis <Bertrand.Marquis@arm.com> 于2022年1月17日周一 17:00写道：
> >>
> >> Hi,
> >>
> >>> On 17 Jan 2022, at 06:40, Dongjiu Geng <gengdongjiu1@gmail.com> wrote:
> >>>
> >>> It turns out that QEMU has been supporting GICv2 virtualization since
> >>> v3.1.0. So remove the dependencies on GICv3. If we want to use GICv3,
> >>> we can select the QEMU_LEGACY configuration.
> >>
> >> I am bit puzzled by this change introducing a legacy option actually selecting the newest GIC interface.
> >>
> >> Can’t we do the opposite and introduce a QEMU_GICV2 instead ?
> >>
> >> Also why do we need to remove gic-v3 support ? The code should actually select which gic to use depending on the device tree.
> >
> > QEMU platfrom only select GICv3,  so I remove this limitation,  let
> > user or developer selects gic version is better.
>
> This is where I am lost, the code is actually always compiling gic-v2 support in unless new vgic is selected (see arch/arm/Makefile).

Yes， so can I think you do not have concern for this patch?

>
> Cheers
> Bertrand
>
> >
> >>
> >> Regards
> >> Bertrand
> >>
> >>>
> >>> Signed-off-by: Dongjiu Geng <gengdongjiu1@gmail.com>
> >>> ---
> >>> 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"
> >>> +     depends on ARM_64
> >>> +     select HAS_PL011
> >>> +     ---help---
> >>> +     Enable all the required drivers for QEMU aarch64 virt emulated
> >>> +     machine.
> >>> +
> >>> +config QEMU_LEGACY
> >>> +     bool "QEMU aarch virt machine support < v3.1.0"
> >>>      depends on ARM_64
> >>>      select GICV3
> >>>      select HAS_PL011
> >>> --
> >>> 2.25.1
>

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

[Julien Grall]

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).

> 
> Signed-off-by: Dongjiu Geng <gengdongjiu1@gmail.com>
> ---
>   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?

@Bertrand, @Stefano, what do you think?

Cheers,

-- 
Julien Grall

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

[Bertrand Marquis]

Hi,

> On 17 Jan 2022, at 14:15, Julien Grall <julien@xen.org> wrote:
> 
> 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).
> 
>> Signed-off-by: Dongjiu Geng <gengdongjiu1@gmail.com>
>> ---
>>  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?
> 
> @Bertrand, @Stefano, what do you think?

I do think that the new Legacy option is very misleading and users will tend to select Qemu instead of the legacy one where having GICv3 makes more sense.
Using the new VGIC which is unsupported is not a standard use case so maybe it would make more sense to create a specific Qemu entry for GICv2 using new VGIC instead and keep the default as is.
To sum up I am no in favour of a solution changing the existing QEMU. A solution creating a new one for the wanted use case would be better for me.

Cheers
Bertrand

> 
> Cheers,
> 
> -- 
> Julien Grall

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

[Dongjiu Geng]

Julien Grall <julien@xen.org> 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.

>
> >
> > Signed-off-by: Dongjiu Geng <gengdongjiu1@gmail.com>
> > ---
> >   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

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

[Bertrand Marquis]

Hi Dongju,

> On 18 Jan 2022, at 08:45, Dongjiu Geng <gengdongjiu1@gmail.com> wrote:
> 
> Julien Grall <julien@xen.org> 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 ?

Cheers
Bertrand

> 
>> 
>>> 
>>> Signed-off-by: Dongjiu Geng <gengdongjiu1@gmail.com>
>>> ---
>>>  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

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

[Dongjiu Geng]

Bertrand Marquis <Bertrand.Marquis@arm.com> 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@gmail.com> wrote:
> >
> > Julien Grall <julien@xen.org> 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!

>
> Cheers
> Bertrand
>
> >
> >>
> >>>
> >>> Signed-off-by: Dongjiu Geng <gengdongjiu1@gmail.com>
> >>> ---
> >>>  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
>

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

[Bertrand Marquis]

Hi Dongju,

> On 18 Jan 2022, at 08:58, Dongjiu Geng <gengdongjiu1@gmail.com> wrote:
> 
> Bertrand Marquis <Bertrand.Marquis@arm.com> 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@gmail.com> wrote:
>>> 
>>> Julien Grall <julien@xen.org> 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.

Do you have a reason to use the NEW_VGIC implementation instead of the standard one ?

Cheers
Bertrand

> 
>> 
>> Cheers
>> Bertrand
>> 
>>> 
>>>> 
>>>>> 
>>>>> Signed-off-by: Dongjiu Geng <gengdongjiu1@gmail.com>
>>>>> ---
>>>>> 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

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

[Dongjiu Geng]

Bertrand Marquis <Bertrand.Marquis@arm.com> 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@gmail.com> wrote:
> >
> > Bertrand Marquis <Bertrand.Marquis@arm.com> 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@gmail.com> wrote:
> >>>
> >>> Julien Grall <julien@xen.org> 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@gmail.com>
> >>>>> ---
> >>>>> 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
>

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

[Julien Grall]

Hi,

On 19/01/2022 15:30, Dongjiu Geng wrote:
> Bertrand Marquis <Bertrand.Marquis@arm.com> 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@gmail.com> wrote:
>>>
>>> Bertrand Marquis <Bertrand.Marquis@arm.com> 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@gmail.com> wrote:
>>>>>
>>>>> Julien Grall <julien@xen.org> 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

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

[Julien Grall]

Hello,

On 18/01/2022 12:58, Dongjiu Geng wrote:
> Bertrand Marquis <Bertrand.Marquis@arm.com> 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@gmail.com> wrote:
>>>
>>> Julien Grall <julien@xen.org> 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!

I would love to get the NEW_VGIC supported. But I think this is 
orthogonal to whether we want to allow CONFIG_QEMU to select it.

If we fully support the new vGIC (i.e vGICv3 is implemented) then it 
would be possible to select it with CONFIG_QEMU as the restriction 
(!GICV3) would not be present.

So I view the change here as temporary. The proposed change will have an 
impact on the existing users (i.e. CONFIG_QEMU will not work out of the 
box anymore when QEMU is configured with GICv3). In addition to that, 
the end solution doesn't look simple. So I think this is not a patch I 
am willing to see temporarily.

One possibility would be to create a new CONFIG for allowing to select 
NEW_VGIC. That said, I don't much like it. So I would say if you want to 
select NEW_VGIC then you want to use defconfig (which should contain 
enough to boot on QEMU with DT).

Cheers,

-- 
Julien Grall