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

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

On Tue, May 30, 2023 at 12:12:44PM -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)
> 
> Ugh, I just noticed that we turned on PCI_COMMAND_MEMORY even though
> BARs 0 and 1 haven't been assigned.  How did that happen?  It looks
> like pci_enable_resources() checks for that, but there must be a hole
> somewhere.

Maybe because BAR2 was assigned? I think pci_enable_resources just
does
                if (r->flags & IORESOURCE_MEM)
                        cmd |= PCI_COMMAND_MEMORY;
in a loop so if any memory BARs are assigned then PCI_COMMAND_MEMORY
is set.

> >    Unable to create vram_mapping
> >    qxl: probe of 0000:01:00.0 failed with error -12