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Message-ID: <vbrnpobomijmzvkhfwupt6oydnb3bmjbrcpf5ctoavuk4lrdyh@d6x5jk2wtxif>
Date: Mon, 8 Jul 2024 10:49:41 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
Suren Baghdasaryan <surenb@...gle.com>,
Vlastimil Babka <vbabka@...e.cz>, Matthew Wilcox <willy@...radead.org>,
sidhartha.kumar@...cle.com, "Paul E . McKenney" <paulmck@...nel.org>,
Bert Karwatzki <spasswolf@....de>, Jiri Olsa <olsajiri@...il.com>,
linux-kernel@...r.kernel.org, Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v3 09/16] mm/mmap: Expand mmap_region() munmap call
* Lorenzo Stoakes <lorenzo.stoakes@...cle.com> [240705 16:36]:
> On Fri, Jul 05, 2024 at 04:30:46PM GMT, Liam R. Howlett wrote:
> > * Lorenzo Stoakes <lorenzo.stoakes@...cle.com> [240705 16:06]:
> > > On Thu, Jul 04, 2024 at 02:27:11PM GMT, Liam R. Howlett wrote:
> > > > From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> > > >
> > > > Open code the do_vmi_align_munmap() call so that it can be broken up
> > > > later in the series.
> > > >
> > > > Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> > > > ---
> > > > mm/mmap.c | 22 +++++++++++++++++++---
> > > > 1 file changed, 19 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/mm/mmap.c b/mm/mmap.c
> > > > index e9858ca8bbd4..f5b33de4e717 100644
> > > > --- a/mm/mmap.c
> > > > +++ b/mm/mmap.c
> > > > @@ -2915,6 +2915,9 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> > > > struct vm_area_struct *next, *prev, *merge;
> > > > pgoff_t pglen = len >> PAGE_SHIFT;
> > > > unsigned long charged = 0;
> > > > + struct vma_munmap_struct vms;
> > > > + struct ma_state mas_detach;
> > > > + struct maple_tree mt_detach;
> > > > unsigned long end = addr + len;
> > > > unsigned long merge_start = addr, merge_end = end;
> > > > bool writable_file_mapping = false;
> > > > @@ -2947,9 +2950,24 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> > > > /* Find the first overlapping VMA */
> > > > vma = vma_find(&vmi, end);
> > > > if (vma) {
> > > > - if (do_vmi_align_munmap(&vmi, vma, mm, addr, end, uf, false))
> > > > + mt_init_flags(&mt_detach, vmi.mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
> > > > + mt_on_stack(mt_detach);
> > > > + mas_init(&mas_detach, &mt_detach, /* addr = */ 0);
> > >
> > > I'm guessing this is exactly equivalent (or equivalent enough for our purposes
> > > here) to the MA_STATE() call in do_vmi_align_munmap()?
> >
> > Yes, what we are doing is inlining the function call so that it can be
> > split to parts. So for reviewing, I just made it in-line.
> >
> > >
> > > Checking the two against each other it seems that it is indeed.
> > >
> > > > + init_vma_munmap(&vms, &vmi, vma, addr, end, uf, /* unlock = */ false);
> > > > + if (vms_gather_munmap_vmas(&vms, &mas_detach))
> > > > + return -ENOMEM;
> > >
> > > In do_vmi_align_munmap() we also invoke vmalidate_mm(), why aren't we doing that
> > > here?
> >
> > I don't see the validate_mm() call in do_vmi_align_munmap, it is called
> > in the vms_complete_munmap_vmas() function though.
>
> In do_vmi_align_munmap() you have:
>
> error = vms_gather_munmap_vmas(&vms, &mas_detach);
> if (error)
> goto gather_failed;
>
> ...
>
> gather_failed:
> validate_mm(mm);
> return error;
>
> >
> > >
> > > > +
> > > > + if (vma_iter_clear_gfp(&vmi, addr, end, GFP_KERNEL))
> > > > return -ENOMEM;
> > >
> > > Same here.
> >
> > It would fail here, our count would be wrong.
>
> Right, but in do_vmi_align_munmap() you have:
>
> error = vma_iter_clear_gfp(vmi, start, end, GFP_KERNEL);
> if (error)
> goto clear_tree_failed;
>
> ...
>
> clear_tree_failed:
> abort_munmap_vmas(&mas_detach);
> gather_failed:
> validate_mm(mm);
>
Right, so I also missed my cleanup in the abort_munmap_vmas() here..
Thanks, I'll fix these.
>
> >
> > >
> > > > +
> > > > + vms_complete_munmap_vmas(&vms, &mas_detach);
> > > > + next = vms.next;
> > > > + prev = vms.prev;
> > > > + vma_prev(&vmi);
> > >
> > > I'm sure this is correct, but just to double-check - we want to set the VMI to
> > > prev here right?
> >
> > Yes. In the current function, the vmi points to prev when we are done
> > this dance - so I put it there.
> > >
> > > It might be worth adding a small cmoment saying '/* vmi now points at prev */'
> > > or similar, I've found it can get quite hard to follow where the iterator is at
> > > sometimes.
> >
> > So this is about to change..
>
> Yeah, I saw :)
>
> >
> > >
> > > > vma = NULL;
> > > > + } else {
> > > > + next = vma_next(&vmi);
> > > > + prev = vma_prev(&vmi);
> > >
> > > But here we move forward to the next VMA and set this to next, then go back to
> > > the _original_ one and this is prev?
> > >
> > > Actually I guess if vma == NULL, next gets you to the next, and prev jumps back
> > > to prev, with nothing between, and so that makes sense.
> >
> > Yes, this is what I'm doing.
> >
> > >
> > >
> > > > }
> > > >
> > > > /*
> > > > @@ -2962,8 +2980,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> > > > vm_flags |= VM_ACCOUNT;
> > > > }
> > > >
> > > > - next = vma_next(&vmi);
> > > > - prev = vma_prev(&vmi);
> > > > if (vm_flags & VM_SPECIAL) {
> > > > if (prev)
> > > > vma_iter_next_range(&vmi);
> > > > --
> > > > 2.43.0
> > > >
> > > >
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