Re: [PATCH] mm: userfaultfd: add UFFDIO_CONTINUE_MODE_WP to install WP PTEs

[Peter Xu <peterx@redhat.com>]

On Tue, Feb 14, 2023 at 02:37:51PM -0800, Axel Rasmussen wrote:
> Agreed, it would likely be a nice cleanup. Peter, any objections? I
> wouldn't mind writing a commit to do this sort of refactor, and rebase
> my change on top of that.

No objection here.  Personally I actually prefer keeping the parameters
around if possible because it's straightforward and no thinking of any
possible indirect accesses all over the place. But maybe growing as long as
8 is still a moot point..  It's just that I don't really know whether it'll
look that good if we put everything into a struct*.

Things like src_start/dst_start/.. do not look good to be there: each layer
could loop over its own range of start/end/... so even if not in the
function parameter we'll need a variable to hold them anyway.

But I do see a few low hanging fruits:

  - I don't see why we need to pass over mmap_changing over all of the
    __mcopy_atomic() callers.  One chance is we simply pass in the ctx* to
    replace "dst_mm + mmap_changing".

  - Merge mcopy_atomic_mode and mode, having last 2 bits for the existing
    three modes, then bit 3 for WP, good enough to set it for the new case.

  - Optionally, we can avoid passing over dst_mm/src_mm all around, when
    dst_vma/src_vma is there?

How about we start from simple?

-- 
Peter Xu