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

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, May 22, 2023 at 04:51:41PM -0500, Bjorn Helgaas wrote:
> 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.


I'd like a stable tag, yes. Just was not sure whom best to ask.



> > ---
> > 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
> >