On 10/27/2026 9:43 AM, Shameer Kolothum Thodi wrote:
>
>
>> -----Original Message-----
>> From: Tushar Dave <[email protected]>
>> Sent: 16 September 2026 19:56
>> To: [email protected]
>> Cc: [email protected]; [email protected]; [email protected];
>> [email protected]; [email protected]; Alex Williamson
>> <[email protected]>; Jason Gunthorpe <[email protected]>; Shameer
>> Kolothum Thodi <[email protected]>
>> Subject: [PATCH 1/5] hw/pci: introduce PCI fixed BAR properties
>>
>> Add fixed-bar-N properties to PCIDevice to allow the guest address
>> of an individual PCI BAR to be explicitly specified. The properties
>> are available for PCI BARs 0 through 5 and accept QEMU size
>> values, for example fixed-bar-0=0x40000000 or fixed-bar-0=64G.
>>
>> e.g.
>> -device some-device,fixed-bar-0=<addr>[,fixed-bar-1=<addr>]...
>>
>> During realize, validate that each specified BAR exists and is a
>> memory BAR, and reject fixed BAR configuration for hot-plugged
>> devices.
>>
>> Signed-off-by: Tushar Dave <[email protected]>
>> ---
>> hw/pci/pci.c | 43 +++++++++++++++++++++++++++++++++++++
>> include/hw/pci/pci_device.h | 7 ++++++
>> 2 files changed, 50 insertions(+)
>>
>> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
>> index 0efb4eb4bb..775fef1beb 100644
>> --- a/hw/pci/pci.c
>> +++ b/hw/pci/pci.c
>> @@ -89,6 +89,12 @@ static const Property pci_props[] = {
>> DEFINE_PROP_STRING("romfile", PCIDevice, romfile),
>> DEFINE_PROP_UINT32("romsize", PCIDevice, romsize, UINT32_MAX),
>> DEFINE_PROP_INT32("rombar", PCIDevice, rom_bar, -1),
>> + DEFINE_PROP_SIZE("fixed-bar-0", PCIDevice, fixed_bar_addr[0],
>> PCI_BAR_UNMAPPED),
>> + DEFINE_PROP_SIZE("fixed-bar-1", PCIDevice, fixed_bar_addr[1],
>> PCI_BAR_UNMAPPED),
>> + DEFINE_PROP_SIZE("fixed-bar-2", PCIDevice, fixed_bar_addr[2],
>> PCI_BAR_UNMAPPED),
>> + DEFINE_PROP_SIZE("fixed-bar-3", PCIDevice, fixed_bar_addr[3],
>> PCI_BAR_UNMAPPED),
>> + DEFINE_PROP_SIZE("fixed-bar-4", PCIDevice, fixed_bar_addr[4],
>> PCI_BAR_UNMAPPED),
>> + DEFINE_PROP_SIZE("fixed-bar-5", PCIDevice, fixed_bar_addr[5],
>> PCI_BAR_UNMAPPED),
>
Thank you for the review.
> These properties are exposed on all PCI devices, but only virt wires up
> the validation and fw_cfg export in this series. On other machines, a
> valid request would be accepted without placing the BAR, right?
Yes.
>
> I think it is better we add a mechanism(MachineClass flag ?) and check
> that.
Sure, I will add a MachineClass flag 'bool pci_fixed_bar_supported'
-Tushar
>
> Thanks,
> Shameer
>
>> DEFINE_PROP_BIT("multifunction", PCIDevice, cap_present,
>> QEMU_PCI_CAP_MULTIFUNCTION_BITNR, false),
>> DEFINE_PROP_BIT("x-pcie-lnksta-dllla", PCIDevice, cap_present,
>> @@ -228,6 +234,36 @@ static void pci_bus_unrealize(BusState *qbus)
>> vmstate_unregister(NULL, &vmstate_pcibus, bus);
>> }
>>
>> +static void pci_check_fixed_bars(PCIDevice *pci_dev, Error **errp)
>> +{
>> + PCIIORegion *r;
>> + int i;
>> +
>> + for (i = 0; i < PCI_NUM_REGIONS - 1; i++) {
>> + if (pci_dev->fixed_bar_addr[i] == PCI_BAR_UNMAPPED) {
>> + continue;
>> + }
>> +
>> + if (DEVICE(pci_dev)->hotplugged) {
>> + error_setg(errp, "fixed-bar-%d is not supported on "
>> + "hot-plugged devices", i);
>> + return;
>> + }
>> +
>> + r = &pci_dev->io_regions[i];
>> + if (!r->size) {
>> + error_setg(errp, "fixed-bar-%d: bar%d does not exist on %s",
>> + i, i, pci_dev->name);
>> + return;
>> + }
>> + if (r->type & PCI_BASE_ADDRESS_SPACE_IO) {
>> + error_setg(errp, "fixed-bar-%d: bar%d on %s is an I/O BAR, "
>> + "not a memory BAR", i, i, pci_dev->name);
>> + return;
>> + }
>> + }
>> +}
>> +
>> static int pcibus_num(PCIBus *bus)
>> {
>> if (pci_bus_is_root(bus)) {
>> @@ -2393,6 +2429,13 @@ static void pci_qdev_realize(DeviceState *qdev,
>> Error **errp)
>> is_default_rom = true;
>> }
>>
>> + pci_check_fixed_bars(pci_dev, &local_err);
>> + if (local_err) {
>> + error_propagate(errp, local_err);
>> + pci_qdev_unrealize(DEVICE(pci_dev));
>> + return;
>> + }
>> +
>> pci_add_option_rom(pci_dev, is_default_rom, &local_err);
>> if (local_err) {
>> error_propagate(errp, local_err);
>> diff --git a/include/hw/pci/pci_device.h b/include/hw/pci/pci_device.h
>> index 5cac6e1688..fc5f50a1c4 100644
>> --- a/include/hw/pci/pci_device.h
>> +++ b/include/hw/pci/pci_device.h
>> @@ -187,6 +187,13 @@ struct PCIDevice {
>> uint32_t max_bounce_buffer_size;
>>
>> char *sriov_pf;
>> +
>> + /*
>> + * fixed_bar_addr[N] holds the guest address configured via the
>> + * fixed-bar-N property for memory BAR N. PCI_BAR_UNMAPPED means
>> + * the BAR's address is not fixed.
>> + */
>> + uint64_t fixed_bar_addr[PCI_NUM_REGIONS - 1];
>> };
>>
>> static inline int pci_intx(PCIDevice *pci_dev)
>> --
>> 2.34.1
>
