linux-kernel - Re: [PATCH v3 08/16] mm/mmap: Inline munmap operation in mmap

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Message-ID: <dkxzq7z6j4u7tmxlsblmupd4la4375z7zkr6mz2vqcfgkswshu@s6ekojjylkxe>
Date: Fri, 5 Jul 2024 16:00:44 -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>, Lorenzo Stoakes <lstoakes@...il.com>,
        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 08/16] mm/mmap: Inline munmap operation in
 mmap_region()

* Lorenzo Stoakes <lorenzo.stoakes@...cle.com> [240705 15:40]:
> On Thu, Jul 04, 2024 at 02:27:10PM GMT, Liam R. Howlett wrote:
> > From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> >
> > mmap_region is already passed sanitized addr and len, so change the
> > call to do_vmi_munmap() to do_vmi_align_munmap() and inline the other
> > checks.
> >
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> > ---
> >  mm/mmap.c | 20 ++++++++++++++------
> >  1 file changed, 14 insertions(+), 6 deletions(-)
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 8d9be791997a..e9858ca8bbd4 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -2937,12 +2937,20 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> >  			return -ENOMEM;
> >  	}
> >
> > -	/* Unmap any existing mapping in the area */
> 
> This feels like an important comment, I know 'find the first overlapping
> VMA' below alludes to it but whenever I've read through this function this
> comment has actually been quite useful to know what the intent is.
> 
> Could we reinstate it?

Ah, sure.  I am going to have to move it around and it sort of loses its
meaning a bit once we gather and complete it (and not actually zero the
tree)..  I'll try to keep it with the correct code block.

> 
> > -	error = do_vmi_munmap(&vmi, mm, addr, len, uf, false);
> > -	if (error == -EPERM)
> > -		return error;
> > -	else if (error)
> > -		return -ENOMEM;
> > +
> > +	if (unlikely(!can_modify_mm(mm, addr, end)))
> > +		return -EPERM;
> > +
> > +	 /* arch_unmap() might do unmaps itself.  */
> > +	arch_unmap(mm, addr, end);
> > +
> > +	/* Find the first overlapping VMA */
> > +	vma = vma_find(&vmi, end);
> > +	if (vma) {
> > +		if (do_vmi_align_munmap(&vmi, vma, mm, addr, end, uf, false))
> > +			return -ENOMEM;
> > +		vma = NULL;
> > +	}
> >
> >  	/*
> >  	 * Private writable mapping: check memory availability
> > --
> > 2.43.0
> >
> >
> 
> Other than trivial point above, LGTM.
> 
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

Thanks!