Re: [PATCH 4/8] acpi_build: Use IOMMU pci device to build IOMMU device ID

On 7/31/2026 3:20 PM, Michael S. Tsirkin wrote:
> On Mon, May 11, 2026 at 06:09:33PM +0530, Sairaj Kodilkar wrote:
>> Currently, build_amd_iommu() uses "addr" property to build the device ID for
>> IOMMU device and advertise it throught IVRS. But this property does not encode
>> IOMMU bus. This will be a problem if IOMMU is attached to different bus.
>> Hence use iommu pci device which provides bus, to build the IOMMU device ID.
>>
>> Signed-off-by: Sairaj Kodilkar <[email protected]>
>> Reviewed-by: Vasant Hegde <[email protected]>
> 
> But is this called after firmware has enumerated the pci bus?
> And I guess OS better not change that bus number eh?
> 

Hi Michael

Yes, the ACPI function is called two times -- during qemu initialization
and firmware writes. During first call, bus numbers are 0 and during
second call, IVRS is created with bus number. This second IVRS
overwrites the first one.

Thanks
Sairaj

>> ---
>>  hw/i386/acpi-build.c | 12 ++++++------
>>  1 file changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
>> index e4ad01eec037..718e3f546b18 100644
>> --- a/hw/i386/acpi-build.c
>> +++ b/hw/i386/acpi-build.c
>> @@ -1752,10 +1752,13 @@ build_amd_iommu(GArray *table_data, BIOSLinker *linker, const char *oem_id,
>>                  const char *oem_table_id)
>>  {
>>      AMDVIState *s = AMD_IOMMU_DEVICE(x86_iommu_get_default());
>> +    PCIDevice *iommu_dev = &(s->pci->dev);
>>      GArray *ivhd_blob = g_array_new(false, true, 1);
>>      AcpiTable table = { .sig = "IVRS", .rev = 1, .oem_id = oem_id,
>>                          .oem_table_id = oem_table_id };
>>      uint64_t feature_report;
>> +    int iommu_bus = pci_bus_num(pci_get_bus(iommu_dev));
>> +    uint16_t iommu_devid = PCI_BUILD_BDF(iommu_bus, iommu_dev->devfn);
>>  
>>      acpi_table_begin(&table, table_data);
>>      /* IVinfo - IO virtualization information common to all
>> @@ -1816,9 +1819,7 @@ build_amd_iommu(GArray *table_data, BIOSLinker *linker, const char *oem_id,
>>      /* IVHD length */
>>      build_append_int_noprefix(table_data, ivhd_blob->len + 24, 2);
>>      /* DeviceID */
>> -    build_append_int_noprefix(table_data,
>> -                              object_property_get_int(OBJECT(s->pci), "addr",
>> -                                                      &error_abort), 2);
>> +    build_append_int_noprefix(table_data, iommu_devid, 2);
>>      /* Capability offset */
>>      build_append_int_noprefix(table_data, s->pci->capab_offset, 2);
>>      /* IOMMU base address */
>> @@ -1850,10 +1851,9 @@ build_amd_iommu(GArray *table_data, BIOSLinker *linker, const char *oem_id,
>>  
>>      /* IVHD length */
>>      build_append_int_noprefix(table_data, ivhd_blob->len + 40, 2);
>> +
>>      /* DeviceID */
>> -    build_append_int_noprefix(table_data,
>> -                              object_property_get_int(OBJECT(s->pci), "addr",
>> -                                                      &error_abort), 2);
>> +    build_append_int_noprefix(table_data, iommu_devid, 2);
>>      /* Capability offset */
>>      build_append_int_noprefix(table_data, s->pci->capab_offset, 2);
>>      /* IOMMU base address */
>> -- 
>> 2.34.1
>