Re: Do we need to unrevert "fs: do not prefault sys_write() user buffer pages"?

[Linus Torvalds]

On Tue, Jun 22, 2021 at 11:51 AM Nadav Amit <nadav.amit@xxxxxxxxx> wrote:
> Just reminding the alternative (in the RFC that I mentioned before):
> a vDSO exception table entry for a memory accessing function in the
> vDSO. It then behaves as a sort of MADV_WILLNEED for the faulting
> page if an exception is triggered. Unlike MADV_WILLNEED it maps the
> page if no IO is needed. It can return through a register whether
> the page was present or not.

Yeah, that looks like a user-space equivalent.

And thanks to the vdso, it doesn't need to support all architectures.
Unlike a kernel model would (but yes, a kernel model could then have a
fallback for the non-prefetching synchronous case instead, so I guess
we could just do one architecture at a time).

               Linus