On 11/1/24 10:47, Marc Zyngier wrote:
On Thu, 11 Jan 2024 09:39:18 +0000,
Philippe Mathieu-Daudé <phi...@linaro.org> wrote:
On 10/1/24 20:53, Philippe Mathieu-Daudé wrote:
The "aarch64" property is added to ARMCPU when the
ARM_FEATURE_AARCH64 feature is available. Rather than
checking whether the QOM property is present, directly
check the feature.
Suggested-by: Markus Armbruster <arm...@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <phi...@linaro.org>
---
hw/arm/virt.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 49ed5309ff..a43e87874c 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -2140,7 +2140,7 @@ static void machvirt_init(MachineState *machine)
numa_cpu_pre_plug(&possible_cpus->cpus[cs->cpu_index],
DEVICE(cpuobj),
&error_fatal);
- aarch64 &= object_property_get_bool(cpuobj, "aarch64",
NULL);
+ aarch64 &= arm_feature(cpu_env(cs), ARM_FEATURE_AARCH64);
So after this patch there are no more use of the ARMCPU "aarch64"
property from code. Still it is exposed via the qom-tree. Thus it
can be set (see aarch64_cpu_set_aarch64). I could understand one
flip this feature to create a custom CPU (as a big-LITTLE setup
as Marc mentioned on IRC), but I don't understand what is the
expected behavior when this is flipped at runtime. Can that
happen in real hardware (how could the guest react to that...)?
I don't think it makes any sense to do that while a guest is running
(and no HW I'm aware of would do this). However, it all depends what
you consider "run time". You could imagine creating a skeletal VM with
all features, and then apply a bunch of changes before the guest
actually runs.
Thanks, this makes sense and confirms my guess.
I don't know enough about the qom-tree and dynamic manipulation of
these properties though, and I'm likely to be wrong about the expected
usage model.
Kevin, Markus, this seems a good example of QOM "config" property that
is RW *before* Realize and should become RO *after* it.
QDev properties has PropertyInfo::realized_set_allowed set to false by
default, but here this property is added at the QOM (lower) layer, so
there is no such check IIUC.
Should "aarch64" become a static QDev property instead (registered via
device_class_set_props -> qdev_class_add_property)?
This just an analyzed example, unfortunately there are many more...
Thanks,
Phil.
