[RFC PATCH v2 00/13] nommu UML

[David Gow]

On Mon, 11 Nov 2024 at 14:27, Hajime Tazaki <thehajime at gmail.com> wrote:
>
> This is a series of patches of nommu arch addition to UML.  It would
> be nice to ask comments/opinions on this.
>
> There are still several limitations/issues which we already found;
> here is the list of those issues.
>
> - prompt configured with /etc/profile is broken (variables are not
>   expanded, ${HOSTNAME%%.*}:$PWD#)
> - there are no mechanism implemented to cache for mapped memory of
>   exec(2) thus, always read files from filesystem upon every exec,
>   which makes slow on some benchmark (lmbench).
>
> -- Hajime
>

Thanks for sending this in!

I had a chance to give this a proper try with KUnit, and think it'd be
a great options to have available: it's certainly nice to have a fast,
easy nommu architecture for testing.

I'd echo the comments from others that — at least for the testing case
— it doesn't make much sense to go to the length to use the fancy
zpoline patching (as neat as it is) compared to a simpler, but slower
seccomp-based approach. It'd be nicer to have a simpler, more robust
implementation first, and if there's a particular reason to want to
speed it up later, zpoline can be added as an option.

Plus, if we can avoid the need for vm.mmap_min_addr, that'd make it
much easier to run the nommu tests alongside all the regular UML ones,
as none would require either root, or an otherwise particularly
special config.

Cheers,
-- David

>
> RFC v2:
> - base branch is now uml/linux.git instead of torvalds/linux.git.
> - reorganize the patch series to clean up
> - fixed various coding styles issues
> - clean up exec code path [07/13]
> - fixed the crash/SIGSEGV case on userspace programs [10/13]
> - add seccomp filter to limit syscall caller address [06/13]
> - detect fsgsbase availability with sigsetjmp/siglongjmp [08/13]
> - removes unrelated changes
> - removes unneeded ifndef CONFIG_MMU
> - convert UML_CONFIG_MMU to CONFIG_MMU as using uml/linux.git
> - proposed a patch of maple-tree issue (resolving a limitation in RFC v1)
>   https://lore.kernel.org/linux-mm/20241108222834.3625217-1-thehajime@gmail.com/
>
> RFC:
> - https://lore.kernel.org/linux-um/cover.1729770373.git.thehajime@gmail.com/
>
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