Comment 57 for bug 314928

Having looked into this further, I find that adding the kernel boot parameter "enable_mtrr_cleanup" does exactly what I'd done in replacing the 4GB entry, and for the same purpose (opening up a range where a new write-combining entry can go). Plus, it's a general algorithm, not something specific to this one motherboard. The sanitizer can be selected by default when compiling the kernel (CONFIG_MTRR_SANITIZER_ENABLE_DEFAULT=1), but Ubuntu doesn't do so.

Looking at this thread:
       http://lkml.org/lkml/2008/4/28/52

it seems that the kernel developers are moving towards using PAT, rather than MTRRs, for the write-combining regions; but the Ubuntu kernel doesn't have PAT enabled.

So people who are getting the "write error: invalid argument" message might try adding that boot parameter.