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Tue, 03 Nov 2026 02:42:37 -0800 (PST) Received: from [192.168.1.22] ([83.231.69.9]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4b2ab00ff3dsm94074165e9.14.2026.11.03.02.42.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 03 Nov 2026 02:42:36 -0800 (PST) Message-ID: <0fdec467-55b0-4354-8bd6-58874c2c20e5@gmail.com> Date: Tue, 3 Nov 2026 11:42:34 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/5] mm/mremap: fix hugetlb reservation leak on partial move To: Josef Bacik , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , David Hildenbrand Cc: Vlastimil Babka , Jann Horn , Pedro Falcato , Muchun Song , Oscar Salvador , linux-mm@kvack.org, stable@vger.kernel.org References: <20261102-b4-mremap-pre-split-v2-0-d281dd11ad7d@toxicpanda.com> <20261102-b4-mremap-pre-split-v2-1-d281dd11ad7d@toxicpanda.com> Content-Language: en-US From: "Jose A. Perez de Azpillaga" In-Reply-To: <20261102-b4-mremap-pre-split-v2-1-d281dd11ad7d@toxicpanda.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 0406CC0002 X-Stat-Signature: t99u8557bbcu7o4pwnhw56re557scx7o X-Rspam-User: X-Spam-Status: No, score=-9.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793702558-526693 X-HE-Meta: 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 fis8yecS 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 11/3/26 12:45 AM, Josef Bacik wrote: > Moving a part of a private hugetlb mapping with mremap() leaks the huge > page reservations of the parts that stay. They are not returned when the > mapping is unmapped, when the process exits or when the pool is resized. > > fixup_hugetlb_reservations() takes the reservation map away from the old > VMA while that VMA still spans its whole range, because the moved part is > only split off by the unmap at the end of the move. hugetlb_vm_op_close() > then finds no map in the parts that remain and returns nothing for them: > > mmap() of 4 pages, MAP_PRIVATE | MAP_HUGETLB HugePages_Rsvd: 4 > mremap() of the second page to a new address HugePages_Rsvd: 4 > munmap() of all of it HugePages_Rsvd: 3 > > The source is unmapped in this case, so the number of VMAs ends up where it > did before and the check against sysctl_max_map_count stays as it is. > > Fix by splitting a hugetlb VMA in prep_move_vma() before a part of it is > moved, as commit 597e4b9ab48a ("mm/mremap: fix locked_vm leak by splitting > VMA for MREMAP_DONTUNMAP") does for an mlock()'d VMA. A backport needs that > commit, which is tagged for stable itself. > > Fixes: 550a7d60bd5e ("mm, hugepages: add mremap() support for hugepage backed vma") > Cc: > Signed-off-by: Josef Bacik > > Reviewed-by: Lorenzo Stoakes (ARM) LGTM: Reviewed-by: Jose A. Perez de Azpillaga -- cheers, jose a. p-a