Hi,
We tried to hot add more than 16 numbers of virtio-blk devices to pci bridge, but found that only 16 of them are available in VM.
There are ‘no space’ error messages in dmesg:
[ 4.666106] pci 0000:00:03.0: PCI bridge to [bus 01]
[ 4.666191] pci 0000:00:03.0: bridge window [io 0x7000-0x7fff]
[ 4.670044] pci 0000:00:03.0: bridge window [mem 0xfe800000-0xfe9fffff]
[ 4.672650] pci 0000:00:03.0: bridge window [mem 0xfcc00000-0xfcdfffff 64bit pref]
[ 4.677876] pci 0000:00:07.0: PCI bridge to [bus 02]
[ 4.677967] pci 0000:00:07.0: bridge window [io 0x6000-0x6fff]
[ 4.681816] pci 0000:00:07.0: bridge window [mem 0xfe600000-0xfe7fffff]
[ 4.684422] pci 0000:00:07.0: bridge window [mem 0xfca00000-0xfcbfffff 64bit pref]
… …
[ 85.779103] pci 0000:02:17.0: [1af4:1001] type 00 class 0x010000
[ 85.779194] pci 0000:02:17.0: reg 0x10: [io 0x0000-0x003f]
[ 85.779235] pci 0000:02:17.0: reg 0x14: [mem 0x00000000-0x00000fff]
[ 85.779812] pci 0000:02:17.0: BAR 1: assigned [mem 0xfe60f000-0xfe60ffff]
[ 85.779835] pci 0000:02:17.0: BAR 0: assigned [io 0x6cc0-0x6cff]
[ 85.779951] virtio-pci 0000:02:17.0: enabling device (0000 -> 0003)
[ 85.833435] virtio-pci 0000:02:17.0: virtio_pci: leaving for legacy driver
[ 85.846894] virtio-pci 0000:02:17.0: irq 61 for MSI/MSI-X
[ 85.846927] virtio-pci 0000:02:17.0: irq 62 for MSI/MSI-X
[ 86.013107] pci 0000:02:18.0: [1af4:1001] type 00 class 0x010000
[ 86.013199] pci 0000:02:18.0: reg 0x10: [io 0x0000-0x003f]
[ 86.013241] pci 0000:02:18.0: reg 0x14: [mem 0x00000000-0x00000fff]
[ 86.013868] pci 0000:02:18.0: BAR 1: assigned [mem 0xfe610000-0xfe610fff]
[ 86.013903] pci 0000:02:18.0: BAR 0: no space for [io size 0x0040]
[ 86.013925] pci 0000:02:18.0: BAR 0: failed to assign [io size 0x0040]
[ 86.014010] virtio-pci 0000:02:18.0: enabling device (0000 -> 0002)
[ 86.057575] virtio-pci 0000:02:18.0: virtio_pci: leaving for legacy driver
[ 86.088217] virtio-pci: probe of 0000:02:18.0 failed with error -12
We went through the kernel codes which processing the hotplug pci devices, the call stack is:
acpi_hotplug_work_fn
–>enable_slot
->__pci_bus_assign_resources
->pci_bus_alloc_resource
->pci_bus_alloc_from_region
->allocate_resource
->find_resource
->pcibios_align_resource
The failure comes with pcibios_align_resource().
resource_size_t
pcibios_align_resource(void *data, const struct resource *res,
resource_size_t size, resource_size_t align)
{
struct pci_dev *dev = data;
resource_size_t start = res->start;
if (res->flags & IORESOURCE_IO) {
if (skip_isa_ioresource_align(dev))
return start;
if (start & 0x300)
start = (start + 0x3ff) & ~0x3ff; àhere.
With the above logic, Only the bellow IO addresses are available for virtio-blk:
[0x6000-0x603f], [0x6040-0x607f], [0x6080-0x60bf], [0x60c0-0x60ff]
[0x6400-0x643f], [0x6440-0x647f], [0x6480-0x64bf], [0x64c0-0x64ff]
[0x6800-0x683f], [0x6840-0x687f], [0x6880-0x68bf], [0x68c0-0x68ff]
[0x6c00-0x6c3f], [0x6c40-0x6c7f], [0x6c80-0x6cbf], [0x6cc0-0x6cff]
So the number is just 16.
We have noticed the comments above pcibios_align_resource():
+/*
+ * We need to avoid collisions with `mirrored' VGA ports
+ * and other strange ISA hardware, so we always want the
+ * addresses to be allocated in the 0x000-0x0ff region
+ * modulo 0x400.
+ *
But we still didn’t quite understand about this, does anyone know about this ?
Or could we skip this checking for standard pci devices ?
Thanks,
Hailiang
