qemu: Remove OVMF X-PciMmio64Mb fw_cfg hint

Modern OVMF (edk2-stable202502 and later) automatically sizes the
64-bit PCI MMIO aperture based on the BARs of actually attached
devices during PCI enumeration. The opt/ovmf/X-PciMmio64Mb fw_cfg
hint is no longer needed to ensure large-BAR devices like NVIDIA
GPUs receive adequate MMIO space.

The previous approach was fragile: the runtime scanned host PCI
devices to estimate the required aperture size, but only considered
GPU devices (class 0x0302), missing NVSwitches and other devices
with large BARs. Removing this code avoids confusion about MMIO
sizing responsibility.

Signed-off-by: Zvonko Kaiser <zkaiser@nvidia.com>

src/runtime/virtcontainers/qemu.go

@@ -815,18 +815,6 @@ func (q *qemu) createPCIeTopology(qemuConfig *govmmQemu.Config, hypervisorConfig
 	// Deduce the right values for mem-reserve and pref-64-reserve memory regions
 	memSize32bit, memSize64bit := q.arch.getBARsMaxAddressableMemory()
 
-	// The default OVMF MMIO aperture is too small for some PCIe devices
-	// with huge BARs so we need to increase it.
-	// memSize64bit is in bytes, convert to MB, OVMF expects MB as a string
-	if strings.Contains(strings.ToLower(hypervisorConfig.FirmwarePath), "ovmf") {
-		pciMmio64Mb := fmt.Sprintf("%d", (memSize64bit / 1024 / 1024))
-		fwCfg := govmmQemu.FwCfg{
-			Name: "opt/ovmf/X-PciMmio64Mb",
-			Str:  pciMmio64Mb,
-		}
-		qemuConfig.FwCfg = append(qemuConfig.FwCfg, fwCfg)
-	}
-
 	// Get the number of hot(cold)-pluggable ports needed from the provided
 	// VFIO devices
 	var numOfPluggablePorts uint32 = 0