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([2a02:8084:e84:2480:228:f8ff:fe6f:83a8]) by smtp.gmail.com with ESMTPSA id s3sm258209wmc.44.2020.12.28.11.12.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 28 Dec 2020 11:12:23 -0800 (PST) Subject: Re: [PATCH 2/6] mm/mremap: For MREMAP_DONTUNMAP check security_vm_enough_memory_mm() To: Brian Geffon Cc: LKML , Dmitry Safonov <0x7f454c46@gmail.com>, Alexander Viro , Andrew Morton , Andy Lutomirski , Catalin Marinas , Dan Williams , Dave Jiang , Hugh Dickins , Ingo Molnar , "Kirill A. Shutemov" , Mike Kravetz , Minchan Kim , Russell King , Thomas Bogendoerfer , Thomas Gleixner , Vishal Verma , Vlastimil Babka , Will Deacon , linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, linux-mm References: <20201013013416.390574-1-dima@arista.com> <20201013013416.390574-3-dima@arista.com> From: Dmitry Safonov Message-ID: Date: Mon, 28 Dec 2020 19:12:21 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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