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Comment by JoshTriplett | Hacker News Reader

With a fair bit of effort; notably, DMA and IOMMUs probably won't work, and most modern devices don't really support PIO. You might be able to boot a really simple environment that runs out of an initramfs though. It's also entirely not obvious to what degree you can use the paging system.

It'd likely be a substantial effort to port Linux.

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Hasn't Intel supported DMA into L3 cache for something like a decade now?

Right, I did not specify what L ;) And the original article did not mention either.

It is supported on true Xeon systems.

I believe that it is not supported in Core CPUs, not even in those of them which were branded as Xeon E or Xeon W.

Sure, I would not expect to do any advanced IO. But right, probably there is no serial console really close to the CPU either, this is not a Raspberry PI. No idea what signals could be used for that.

Page tables I am not sure either. Could you still do it like in Linux 1.0? No idea what things looked like then, but I assume much less dedicated hardware support.

> probably there is no serial console really close to the CPU either

outb to 0x3f8 might work.

I know there were once versions of Linux that supported running without an MMU. Those versions, with very limited hardware support, might work in this mode.

It's still part of the kernel code: https://www.kernel.org/doc/Documentation/nommu-mmap.txt

And apparently, good enough to run DOOM: https://hackaday.com/2022/12/07/a-tiny-risc-v-emulator-runs-...

Substantial effort I don't doubt. First probably years of learning how things work under the hood for most normal mortals.

DMA on x86 does update contents of CPU caches.

Yes, it does, but that doesn't mean the hardware necessarily supports doing it without a memory controller.

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