Re: [PATCH v2] PCI: acpiphp: Reassign resources on bridge if necessary

Bjorn Helgaas
2023-05-22T21:51:47Z

On Mon, Apr 24, 2023 at 09:15:57PM +0200, Igor Mammedov wrote:
> When using ACPI PCI hotplug, hotplugging a device with
> large BARs may fail if bridge windows programmed by
> firmware are not large enough.
>
> Reproducer:
> $ qemu-kvm -monitor stdio -M q35 -m 4G \
> -global ICH9-LPC.acpi-pci-hotplug-with-bridge-support=on \
> -device id=rp1,pcie-root-port,bus=pcie.0,chassis=4 \
> disk_image
>
> wait till linux guest boots, then hotplug device
> (qemu) device_add qxl,bus=rp1
>
> hotplug on guest side fails with:
> pci 0000:01:00.0: [1b36:0100] type 00 class 0x038000
> pci 0000:01:00.0: reg 0x10: [mem 0x00000000-0x03ffffff]
> pci 0000:01:00.0: reg 0x14: [mem 0x00000000-0x03ffffff]
> pci 0000:01:00.0: reg 0x18: [mem 0x00000000-0x00001fff]
> pci 0000:01:00.0: reg 0x1c: [io 0x0000-0x001f]
> pci 0000:01:00.0: BAR 0: no space for [mem size 0x04000000]
> pci 0000:01:00.0: BAR 0: failed to assign [mem size 0x04000000]
> pci 0000:01:00.0: BAR 1: no space for [mem size 0x04000000]
> pci 0000:01:00.0: BAR 1: failed to assign [mem size 0x04000000]
> pci 0000:01:00.0: BAR 2: assigned [mem 0xfe800000-0xfe801fff]
> pci 0000:01:00.0: BAR 3: assigned [io 0x1000-0x101f]
> qxl 0000:01:00.0: enabling device (0000 -> 0003)
> Unable to create vram_mapping
> qxl: probe of 0000:01:00.0 failed with error -12
>
> However when using native PCIe hotplug
> '-global ICH9-LPC.acpi-pci-hotplug-with-bridge-support=off'
> it works fine, since kernel attempts to reassign unused resources.
> Use the same machinery as native PCIe hotplug to (re)assign resources.
>
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>

Tentatively applied to pci/hotplug for v6.5.

Tentative only because I'm hoping for your ack or review, Rafael (I
see you acked v1, but this one is a little different).

And I think you'd like a stable tag, Michael? I'm happy to add one,
but wasn't sure if you wanted a separate ack for that.

> ---
> tested in QEMU with Q35 machine on PCIE root port and also
> with nested conventional bridge attached to root port.
>
> v2:
> * fixup subject to match expected style
> * drop no longer needed __pci_bus_size_bridges() to avoid
> memory leak (Bjorn Helgaas <helgaas@kernel.org>)
> ---
> drivers/pci/hotplug/acpiphp_glue.c | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/drivers/pci/hotplug/acpiphp_glue.c b/drivers/pci/hotplug/acpiphp_glue.c
> index 5b1f271c6034..328d1e416014 100644
> --- a/drivers/pci/hotplug/acpiphp_glue.c
> +++ b/drivers/pci/hotplug/acpiphp_glue.c
> @@ -498,7 +498,6 @@ static void enable_slot(struct acpiphp_slot *slot, bool bridge)
> acpiphp_native_scan_bridge(dev);
> }
> } else {
> - LIST_HEAD(add_list);
> int max, pass;
>
> acpiphp_rescan_slot(slot);
> @@ -512,12 +511,10 @@ static void enable_slot(struct acpiphp_slot *slot, bool bridge)
> if (pass && dev->subordinate) {
> check_hotplug_bridge(slot, dev);
> pcibios_resource_survey_bus(dev->subordinate);
> - __pci_bus_size_bridges(dev->subordinate,
> - &add_list);
> }
> }
> }
> - __pci_bus_assign_resources(bus, &add_list, NULL);
> + pci_assign_unassigned_bridge_resources(bus->self);
> }
>
> acpiphp_sanitize_bus(bus);
> --
> 2.39.1
>