Re: [PATCH v5 5/5] hw/arm/virt: Let the virtio-iommu bypass MSIs

[Auger Eric <eric.auger@redhat.com>]

Hi Peter,

On 6/25/20 12:01 PM, Peter Maydell wrote:
> On Wed, 24 Jun 2020 at 14:27, Eric Auger <eric.auger@redhat.com> wrote:
>>
>> At the moment the virtio-iommu translates MSI transactions.
>> This behavior is inherited from ARM SMMU. The virt machine
>> code knows where the guest MSI doorbells are so we can easily
>> declare those regions as VIRTIO_IOMMU_RESV_MEM_T_MSI. With that
>> setting the guest will not map MSIs through the IOMMU and those
>> transactions will be simply bypassed.
>>
>> Depending on which MSI controller is in use (ITS or GICV2M),
>> we declare either:
>> - the ITS interrupt translation space (ITS_base + 0x10000),
>>   containing the GITS_TRANSLATOR or
>> - The GICV2M single frame, containing the MSI_SETSP_NS register.
>>
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>> Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
>>
> 
>>  static void virt_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
>>                                              DeviceState *dev, Error **errp)
>>  {
>> +    VirtMachineState *vms = VIRT_MACHINE(hotplug_dev);
>> +
>>      if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
>>          virt_memory_pre_plug(hotplug_dev, dev, errp);
>> +    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
>> +        /* we declare a VIRTIO_IOMMU_RESV_MEM_T_MSI region */
>> +
>> +        if (vms->msi_controller == VIRT_MSI_CTRL_ITS) {
>> +            /* GITS_TRANSLATER page */
>> +            qdev_prop_set_uint32(dev, "len-reserved-regions", 1);
>> +            qdev_prop_set_string(dev, "reserved-regions[0]",
>> +                                 "0x8090000:0x809FFFF:1");
>> +        } else if (vms->msi_controller == VIRT_MSI_CTRL_GICV2M) {
>> +            /* MSI_SETSPI_NS page */
>> +            qdev_prop_set_uint32(dev, "len-reserved-regions", 1);
>> +            qdev_prop_set_string(dev, "reserved-regions[0]",
>> +                                 "0x8020000:0x8020FFF:1");
> 
> This hardcodes addresses and lengths that are in the
> base_memmap[] array for VIRT_GIC_ITS and VIRT_GIC_V2M,
> so it's setting up a bear trap if we ever decide to
> move those. Could we construct the string from the
> base_memmap[] array entry values instead, please ?
Sure

Eric
> 
> thanks
> -- PMM
>