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From:   Brian Geffon <bgeffon@google.com>
Date:   Mon, 28 Dec 2020 10:21:56 -0800
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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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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.