On Sat, 20 Sept 2025 at 15:02, Mohamed Mediouni
<moha...@unpredictable.fr> wrote:
>
> On Hypervisor.framework for macOS and WHPX for Windows, the provided
> environment is a GICv3 without ITS.
>
> As such, support a GICv3 w/ GICv2m for that scenario.
>
> Signed-off-by: Mohamed Mediouni <moha...@unpredictable.fr>
>
> Reviewed-by: Pierrick Bouvier <pierrick.bouv...@linaro.org>
> ---
> hw/arm/virt-acpi-build.c | 4 +++-
> hw/arm/virt.c | 8 ++++++++
> include/hw/arm/virt.h | 2 ++
> 3 files changed, 13 insertions(+), 1 deletion(-)
Looking at this I find myself wondering whether we need the
old-version back compat handling. The cases I think we have
at the moment are:
(1) TCG, virt-6.1 and earlier: no_tcg_its is set
-- you can have a gicv2 (always with a gicv2m)
-- if you specify gic-version=3 you get a GICv3 without ITS
(2) TCG, virt-6.2 and later:
-- gic-version=2 still has gicv2m
-- gic-version=3 by default gives you an ITS; if you also
say its=off you get GICv3 with no ITS
-- there is no case where we provide a GICv3 and are
unable to provide an ITS for it
(3) KVM (any version):
-- gic-version=2 has a gicv2m
-- gic-version=3 gives you an ITS by default; its=off
will remove it
-- there is no case where we provide a GICv3 and are
unable to provide an ITS for it
(4) HVF:
-- only gic-version=2 works, you get a gicv2m
and I think what we want is:
(a) if you explicitly disable the ITS (with its=off or via
no_tcg_its) you get no ITS (and no gicv2m)
(b) if you explicitly enable the ITS you should get an
actual ITS or an error message
(c) the default should be its=auto which gives
you "ITS if we can, gicv2m if we can't".
This is repurposing the its= property as "message signaled
interrupt support", which is a little bit of a hack
but I think OK if we're clear about it in the docs.
(We could rename the property to "msi=(off,its,gicv2m,auto)"
with back-compat support for "its=" but I don't know if
that's worth the effort.)
And then that doesn't need any back-compat handling for pre-10.2
machine types or a "no_gicv3_with_gicv2m" flag, because for
10.1 and earlier there is no case that currently works and
which falls into category (c) and which doesn't give you an ITS.
(because we don't yet have hvf gicv3 implemented: that's a new
feature that never worked in 10.1.)
What do you think?
thanks
-- PMM
