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
