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From:   Brian Geffon <bgeffon@google.com>
Date:   Wed, 30 Dec 2020 07:43:42 -0800
Message-ID: <CADyq12w0+ZA6nwJOtJJ-66vHuq4aWwQw22NOUymz7KQa9DXqHQ@mail.gmail.com>
Subject: Re: [PATCH 2/6] mm/mremap: For MREMAP_DONTUNMAP check security_vm_enough_memory_mm()
To:     Dmitry Safonov <dima@arista.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Hugh Dickins <hughd@google.com>,
        Ingo Molnar <mingo@redhat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Minchan Kim <minchan@kernel.org>,
        Russell King <linux@armlinux.org.uk>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vishal Verma <vishal.l.verma@intel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Will Deacon <will@kernel.org>, linux-aio@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-mm <linux-mm@kvack.org>
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Ah, you're right. This individual patch looks good to me.

Brian

On Mon, Dec 28, 2020 at 11:12 AM Dmitry Safonov <dima@arista.com> wrote:
>
> On 12/28/20 6:21 PM, Brian Geffon wrote:
> > This looks good to me with a small comment.
> >
> >>         if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) {
> >>                 /* OOM: unable to split vma, just get accounts right */
> >> -               if (vm_flags & VM_ACCOUNT)
> >> +               if (vm_flags & VM_ACCOUNT && !(flags & MREMAP_DONTUNMAP))
> >>                         vm_acct_memory(new_len >> PAGE_SHIFT);
> >
> > Checking MREMAP_DONTUNMAP in the do_munmap path is unnecessary as
> > MREMAP_DONTUNMAP will have already returned by this point.
>
> In this code it is also used as err-path. In case move_page_tables()
> fails to move all page tables or .mremap() callback fails, the new VMA
> is unmapped.
>
> IOW, MREMAP_DONTUNMAP returns under:
> :       if (unlikely(!err && (flags & MREMAP_DONTUNMAP))) {
>
> --
>           Dima