> On 12. Jan 2026, at 10:45, Shameer Kolothum <skolothumtho@nvidia.com> wrote:
>
>
>
>> -----Original Message-----
>> From: Mohamed Mediouni <mohamed@unpredictable.fr>
>> Sent: 11 January 2026 21:44
>> To: Shameer Kolothum <skolothumtho@nvidia.com>
>> Cc: qemu-arm@nongnu.org; qemu-devel@nongnu.org;
>> eric.auger@redhat.com; peter.maydell@linaro.org; Jason Gunthorpe
>> <jgg@nvidia.com>; Nicolin Chen <nicolinc@nvidia.com>;
>> ddutile@redhat.com; berrange@redhat.com; clg@redhat.com;
>> alex@shazbot.org; Nathan Chen <nathanc@nvidia.com>; Matt Ochs
>> <mochs@nvidia.com>; smostafa@google.com; wangzhou1@hisilicon.com;
>> jiangkunkun@huawei.com; jonathan.cameron@huawei.com;
>> zhangfei.gao@linaro.org; zhenzhong.duan@intel.com; yi.l.liu@intel.com;
>> Krishnakant Jaju <kjaju@nvidia.com>
>> Subject: Re: [PATCH v7 17/36] hw/arm/virt: Set msi-gpa property
>>
>> External email: Use caution opening links or attachments
>>
>>
>>> On 11. Jan 2026, at 20:53, Shameer Kolothum <skolothumtho@nvidia.com>
>> wrote:
>>>
>>> Set the MSI doorbell GPA property for accelerated SMMUv3 devices for use
>>> by KVM MSI setup. Also, since any meaningful use of vfio-pci devices with
>>> an accelerated SMMUv3 requires both KVM and a kernel irqchip, ensure
>>> those are specified when accel=on is selected.
>>>
>>> Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
>>> Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>
>>> ---
>>> hw/arm/virt.c | 20 ++++++++++++++++++++
>>> 1 file changed, 20 insertions(+)
>>>
>>> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
>>> index 9d0568a7d5..08feadf0a8 100644
>>> --- a/hw/arm/virt.c
>>> +++ b/hw/arm/virt.c
>>> @@ -3052,6 +3052,26 @@ static void
>> virt_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
>>> /* The new SMMUv3 device is specific to the PCI bus */
>>> object_property_set_bool(OBJECT(dev), "smmu_per_bus", true,
>> NULL);
>>> }
>>> + if (object_property_find(OBJECT(dev), "accel") &&
>>> + object_property_get_bool(OBJECT(dev), "accel", &error_abort)) {
>>> + hwaddr db_start;
>>> +
>>> + if (!kvm_enabled() || !kvm_irqchip_in_kernel()) {
>>> + error_setg(errp, "SMMUv3 accel=on requires KVM with "
>>> + "kernel-irqchip=on support");
>>> + return;
>>> + }
>>> +
>>> + if (vms->msi_controller == VIRT_MSI_CTRL_ITS) {
>>> + /* GITS_TRANSLATER page + offset */
>>> + db_start = base_memmap[VIRT_GIC_ITS].base + 0x10000 + 0x40;
>>> + } else {
>>> + /* MSI_SETSPI_NS page + offset */
>>> + db_start = base_memmap[VIRT_GIC_V2M].base + 0x40;
>>> + }
>> Hello,
>>
>> Currently (but soon no longer the case for virt-11.0+), its=off means no MSI
>> controller at all instead of
>> GICv3 + GICv2m.
>>
>> Would an else if with an error returned if no MSI controller is enabled be
>> adequate?
>
> The MSI doorbell setup here is only required for MSI translation cases.
> When ITS is off (and no MSI controller is present), passthrough devices
> cannot use MSI/MSI-X, so no MSI translation is required. Is that right?
>
> If so, skipping the doorbell setup is expected and correct, and returning
> an error would unnecessarily reject a valid configuration.
Hello,
Could it be better then to have an else if for the GICv2m case and a separate
else with setting db_start to 0 or something instead of an invalid (because not
present device) address to make things clearer?
Thank you,
-Mohamed
> Thanks,
> Shameer
>