> -----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),
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?
I think it is better we add a mechanism(MachineClass flag ?) and check
that.
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
