# Having pci config memory mapped access enabled is hindering the FreeBSD 11.1 installation



## Rajesh (Jun 26, 2018)

Hi,

Recently, I came across an issue while Installing FreeBSD 11.1 in one of my machines. The issue is system panics and reboots every time when I try to install FreeBSD.  After doing some debugging and google search, I could get the installation done with tunable "hw.pci.mcfg" set to 0. 

Reading through google search and other references, setting hw.pci.mcfg to 0 (by default it's enabled it seems) basically disables the memory mapped access of PCI configuration space.  So, question is why having that enabled is causing trouble?  What could be the possible reasons?

Another related question.  What is that ACPI MCFG table? Does BIOS populate these tables and gives reference to the kernel or something? or Is it something that the kernel itself builds during the boot process?  Any reading references available to understand about this tables?

Please let me know if you need any other details.


----------

