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) {
--
2.19.1.3.g30247aa5d201
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