On 6/4/19 11:44 PM, Laszlo Ersek wrote: > When assigning a physical PCIe device to a QEMU/KVM guest, PciBusDxe may > find that the extended config space is not (fully) implemented. In > LocatePciExpressCapabilityRegBlock(), "CapabilityEntry" may be read as > 0xFFFF_FFFF at a given config space offset, after which the loop gets > stuck spinning on offset 0xFFC (the read at offset 0xFFC returns > 0xFFFF_FFFF most likely as well). > > Another scenario (not related to virtualization) for triggering the above > is when a Conventional PCI bus -- exposed by a PCIe-to-PCI bridge in the > topology -- intervenes between a PCI Express Root Port and a PCI Express > Endpoint. The Conventional PCI bus limits the accessible config space of > the PCI Express Endpoint, even though the endpoint advertizes the PCI > Express capability. Here's a diagram, courtesy of Alex Williamson: > > [PCIe Root Port]--[PCIe-to-PCI]--[PCI-to-PCIe]--[PCIe EP] > ->| |<- Conventional PCI bus > > Catch reads of 0xFFFF_FFFF in LocatePciExpressCapabilityRegBlock(), and > break out of the scan with a warning message. The function will return > EFI_NOT_FOUND. > > Cc: Alex Williamson <alex.william...@redhat.com> > Cc: Hao A Wu <hao.a...@intel.com> > Cc: Jian J Wang <jian.j.w...@intel.com> > Cc: Ray Ni <ray...@intel.com> > Cc: Star Zeng <star.z...@intel.com> > Signed-off-by: Laszlo Ersek <ler...@redhat.com> > --- > > Notes: > Repo: https://github.com/lersek/edk2.git > Branch: pcibus_no_ext_conf > > MdeModulePkg/Bus/Pci/PciBusDxe/PciCommand.c | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciCommand.c > b/MdeModulePkg/Bus/Pci/PciBusDxe/PciCommand.c > index 214aeecdd40a..6283d602207c 100644 > --- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciCommand.c > +++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciCommand.c > @@ -236,6 +236,19 @@ LocatePciExpressCapabilityRegBlock ( > break; > } > > + if (CapabilityEntry == MAX_UINT32) { > + DEBUG (( > + DEBUG_WARN, > + "%a: [%02x|%02x|%02x] failed to access config space at offset > 0x%x\n", > + __FUNCTION__, > + PciIoDevice->BusNumber, > + PciIoDevice->DeviceNumber, > + PciIoDevice->FunctionNumber, > + CapabilityPtr > + )); > + break; > + } > + > CapabilityID = (UINT16) CapabilityEntry; > > if (CapabilityID == CapId) { >
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