Messages in this thread | | | From | Bjorn Helgaas <> | Date | Mon, 24 Jun 2013 21:35:21 -0600 | Subject | Re: [PATCH] PCI: avoid NULL deref in alloc_pcie_link_state |
| |
On Mon, Jun 24, 2013 at 8:58 PM, Alex Williamson <alex.williamson@redhat.com> wrote: > On Mon, 2013-06-24 at 19:38 -0600, Bjorn Helgaas wrote: >> [+cc Michael, Alex, Isaku] >> >> On Wed, Jun 19, 2013 at 12:56 PM, Radim Krčmář <rkrcmar@redhat.com> wrote: >> > PCIe switch upstream port can be connected directly to the PCIe root bus >> > in QEMU; ASPM does not expect this topology and dereferences NULL pointer >> > when initializing. >> > >> > I have not confirmed this can happen on real hardware, but it is presented >> > as a feature in QEMU, so there is no reason to panic if we can recover. >> >> This doesn't seem like a valid hardware topology to me. If this *can* >> occur on real hardware, we should fix it in Linux. If not, maybe QEMU >> should be changed to disallow it. > > I think a quad-port 82576 plugged into an express slot is likely the > same topology.
I don't think that would be the same topology Radim described. In Radim's case, we have this:
00:03.0 upstream port 01:00.0 downstream port
and when we call alloc_pcie_link_state() for 01:00.0,
pdev is 01:00.0 pdev->bus is bus 01 pdev->bus->parent is bus 00 pdev->bus->parent->self (the bridge device leading to bus 00) is NULL
But in the case of a quad 82576 plugged into a slot, there would be a root port or a downstream port leading to the slot's link, so my guess is we'd have something like this (based on lspci output I found at [1]):
00:05.0 root port leading to slot (bridge to [bus 01-08]) 01:00.0 upstream port of switch on card (bridge to [bus 02-08]) 02:02.0 downstream port (bridge to [bus 03-05]) 02:04.0 downstream port (bridge to [bus 06-08]) 03:00.0 82576 port 0 03:00.1 82576 port 1 06:00.0 82576 port 2 06:00.1 82576 port 3
So when we call alloc_pcie_link_state() for 02:02.0,
pdev is 02:02.0 pdev->bus is bus 02 pdev->bus->parent is bus 01 pdev->bus->parent->self (the bridge leading to bus 01) is 00:05.0
Bjorn
[1] http://sourceforge.net/p/e1000/bugs/112/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |