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b=loQMtHqhalWO4rrYjIyRPKyEqjWxTZb6BlwdL5msNmZ8vSyAYVwkoIlITK/EK6whQ ZB+Jv8FruDmizIGOrPFJrvnlhcfGT7tekhMTGIdaJUaeMXK8p3ngk/bK7NSokD/72A EPXGc9PrDcuHucNhjspOyshkHtW+v4llb8UqktVOZ/HAsfRGXJqRAU6FxB93cTB8Z3 x0MJEAXYRmT21ynaXaRjgAsl1ndks8kOc+vXwkIRWoUfXg/I0rria48CtbBn8KGvwH LHNEE6u+SkLTWR4oMnNkLnHKCUWu4FIhu72ADkGKSv/yU+dZwf4ls+R4gn62e/OzTk I1q22ctgf2IYw== Message-ID: <37a204f2-796d-4d15-b21b-09fd4a9e77c2@kernel.org> Date: Fri, 20 Mar 2026 09:10:04 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/huge_memory: fix folio isn't locked in softleaf_to_folio() To: Jinjiang Tu , Andrew Morton Cc: lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, baohua@kernel.org, ryan.roberts@arm.com, linux-mm@kvack.org, wangkefeng.wang@huawei.com, sunnanyong@huawei.com References: <20260319012541.4158561-1-tujinjiang@huawei.com> <20260319155101.f7a62c04a7bcfc838b63824c@linux-foundation.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 1656CA000B X-Stat-Signature: bw1sgdj4rsdy5tez5j85dbt9ncpwfkbj X-Rspam-User: X-HE-Tag: 1773994210-952268 X-HE-Meta: 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 l0d8/SO3 +KPlPNXJNmmJ2T1NrT2iWylRvaeU+aJHDca4O6/XL3esl/TKCrPzWaDlDptm5k/+9XuaPKs4DIwPy0RASfTjpTIMjqMAuT5gzkLfVT5RvMdoLnEqCuieylKwPX4170eyq410q08yooMDegU0SR0KW0adiWNwItnhkDZh6qugK4sh8YtUOPaVXNQRMVSbuRv3PatABfut+gZrg3HZ7YF0K6AmyVtJH2H8xy3iIrCHFpn6S+rJD6MC3bOxZRrdGhhHtNVBJUVlY2Y0C468vT0tcgj3qrtnQII10k8rO4FGuu080BVLdr955JJs9CUqYetwoVBowaHDcraYCy3hraJFAqKUM5tuK9Y6EEf7/ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/20/26 02:52, Jinjiang Tu wrote: > > 在 2026/3/20 6:51, Andrew Morton 写道: >> On Thu, 19 Mar 2026 09:25:41 +0800 Jinjiang Tu >> wrote: >> >>> On arm64 server, we found folio that get from migration entry isn't >>> locked >>> in softleaf_to_folio(). This issue triggers when mTHP splitting and >>> zap_nonpresent_ptes() races, and the root cause is lack of memory >>> barrier >>> in softleaf_to_folio(). The race is as follows: >>> >>>     CPU0                                             CPU1 >>> >>> deferred_split_scan()                              zap_nonpresent_ptes() >>>    lock folio >>>    split_folio() >>>      unmap_folio() >>>        change ptes to migration entries >>>      __split_folio_to_order()                         >>> softleaf_to_folio() >>>        set flags(including PG_locked) for tail pages    folio = >>> pfn_folio(softleaf_to_pfn(entry)) >>>        smp_wmb()                                        >>> VM_WARN_ON_ONCE(!folio_test_locked(folio)) >>>        prep_compound_page() for tail pages >>> >>> In __split_folio_to_order(), smp_wmb() guarantees page flags of tail >>> pages >>> are visible before the tail page becomes non-compound. smp_wmb() should >>> be paired with smp_rmb() in softleaf_to_folio(), which is missed. As a >>> result, if zap_nonpresent_ptes() accesses migration entry that stores >>> tail pfn, softleaf_to_folio() may see the updated compound_head of tail >>> page before page->flags. >> Please describe the userspace-visible runtime effects of this bug. > > This issue will trigger VM_WARN_ON_ONCE() in pfn_swap_entry_folio(). But the impact is bigger, right, when callers rely on folio_test_anon() etc? -- Cheers, David