linux-kernel - Re: [PATCH 4/7] mm/mremap: Replace can_modify_mm with can_modify

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Message-ID: <CAKbZUD2hCWoFb4s8ZbGfa7-ejTXbRjMg0wswuo-A2Y8wyomL8A@mail.gmail.com>
Date: Wed, 7 Aug 2024 01:59:24 +0100
From: Pedro Falcato <pedro.falcato@...il.com>
To: Jeff Xu <jeffxu@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Vlastimil Babka <vbabka@...e.cz>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, oliver.sang@...el.com, 
	torvalds@...ux-foundation.org, Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH 4/7] mm/mremap: Replace can_modify_mm with can_modify_vma

On Wed, Aug 7, 2024 at 12:09 AM Jeff Xu <jeffxu@...gle.com> wrote:
>
> On Tue, Aug 6, 2024 at 2:28 PM Pedro Falcato <pedro.falcato@...il.com> wrote:
> >
> > Delegate all can_modify checks to the proper places. Unmap checks are
> > done in do_unmap (et al).
> >
> > This patch allows for mremap partial failure in certain cases (for
> > instance, when destination VMAs aren't sealed, but the source VMA is).
> > It shouldn't be too troublesome, as you'd need to go out of your way to
> > do illegal operations on a VMA.
> >
> > Signed-off-by: Pedro Falcato <pedro.falcato@...il.com>
> > ---
> >  mm/mremap.c | 33 +++++++--------------------------
> >  1 file changed, 7 insertions(+), 26 deletions(-)
> >
> > diff --git a/mm/mremap.c b/mm/mremap.c
> > index e7ae140fc64..8af877d7bb0 100644
> > --- a/mm/mremap.c
> > +++ b/mm/mremap.c
> > @@ -676,6 +676,9 @@ static unsigned long move_vma(struct vm_area_struct *vma,
> >         if (unlikely(flags & MREMAP_DONTUNMAP))
> >                 to_account = new_len;
> >
> > +       if (!can_modify_vma(vma))
> > +               return -EPERM;
> > +
> I m not 100% sure, but I suspect you don't need this check? Is
> vma_to_resize already checking the src address ?

Hmm, yes, good point.

>
> PS. Is it possible to consolidate all the related changes (except the
> fix for madvise) to a single commit ?

The patch set is organized logically, in simple clear steps. As a
maintainer, I would prefer to review something like this vs a big
confusing patch that touches many things at once.
Of course if the maintainers think this is too coarse (it's not
exactly a large patch set, just moves a lot of code back and forth),
I'm happy to merge these into larger chunks.

>  It would be easier to look for dependency, e.g. the remap depends on munmap().

All patches depend on the previous (and a single patch would make it
harder to see these dependencies). The kernel should build and the
selftests should pass for every patch in the set.

>
> Also selftest is helpful to prove the correctness of the change. (And
> I can also test it)

I have run selftests, and it is.

-- 
Pedro