On Mon, 2025-11-10 at 21:18 +0900, Hajime Tazaki wrote: > > What is it for ? > ================ > > - Alleviate syscall hook overhead implemented with ptrace(2) > - To exercises nommu code over UML (and over KUnit) > - Less dependency to host facilities
FWIW, in some way, this order of priorities is exactly why this hasn't been going anywhere, and every time I looked at it I got somewhat annoyed by what seems to me like choices made to support especially the first bullet. I suspect that the first and third bullet are not even really true any more, since you moved to seccomp (per our request), yet I think design choices influenced by them persist. People are definitely interested in the second bullet, mostly for kunit, and I'd be willing to support them in that to some extent. However, I'm not yet convinced that all of the complexities presented in this patchset (such as completely separate seccomp implementation) are actually necessary in support of _just_ the second bullet. These seem to me like design choices necessary to support the _first_ bullet [1]. [1] and then I suppose the third, which I'm reading as "doesn't need seccomp or ptrace", but I'm not really quite sure what you meant I've thought about what would happen if we stuck to creating a (single) separate process on the host to execute userspace, and just used CLONE_VM for it. That way, it's still no-MMU with full memory access, but there's some implicit isolation between the kernel and userspace processes which will likely remove complexities around FP/SSE/AVX handling, may completely remove the need for a separate seccomp implementation, etc. It would, on the other hand, make it completely non-viable to achieve the first and third bullets, so given your pursuit of those, one some level I understand the design right now. I'm yet to be convinced, however, that those are even worthy goals for (upstream) UML, what use case would that enable that we really need? Especially considering that over a longer perspective, NOMMU architectures _are_ on their way out, and UML will certainly follow once that happens, it won't be the last remaining NOMMU architecture. So the only value I see in this is for testing over the net couple of years, which really doesn't need any sort of significant optimisation or less reliance on host facilities. Where do you see this differently? johannes
