For the past several weeks I had a strange problem. Sometimes when I booted my computer, it would refuse to start the X server and would give the following error in dmesg:
NVRM: not using NVAGP, kernel was compiled with GART_IOMMU support!!
NVRM: failed to allocate stack!
The weird thing about it is that normally if I rebooted the computer it would magically work again. So this error only showed up once-in a while and seemed to disappear at will. Today, it happened again, so I decided to fix it.
The first thing that I tried was disabling the GART_IOMMU option in the kernel. Unfortunately, it now embedded in AMD64, so it can’t be easily disabled. So I opened up lynx (as I said I had no X server) and googled around. Some other people experienced similar problems. In the NVIDIA forums someone suggested adding iommu=noaperture to the kernel options at startup, or enlarging the aperture size in the bios. Changing the aperture size was suggested for couple of other problem, and I remembered that is some point the agppart complained about the aperture size.
I decided to change the aperture size. To do so I entered the bios and pressed Ctrl+F1. This shows up some more advanced configuration options. The aperture size option was under “Advanced Chipset Options”, I changed it to 64MB and I rebooted the computer.
Now everything seems to work properly, I just hope it was really solved and no just accidentally work like at the past. The good thing I can’t see any errors from the NVIDIA driver in dmesg anymore.