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b=V4FsFf3AtON/wgsLo5m4+/ZiZPG3wfTMu7h8ZgJgMHhQBildsS+RYKcSF4yapYu7x 2fBjExeGFITlfk69dT226peFZQEXUs9Tmch/ktwXz4SS8sVW5rdkfP+5yChyAYbhT1 GBFhr0Kwao8weO2Z79MRIGNUkSbRl8uemIyLATdAWnGXs1wKHgrLgmk2JF6gvuRcXj kFwdgtS/GlSCBg5KXTWbDFu7/lymgd8Spk+1VNX7CBEX2qwnmf6QGjeDawt+f753f6 Hg/d4rEUIAh06B6x1CIBjXvS9LOkRBI8hgFznJwt3pb+/hm27jUtnkIsBfLNvI/8O1 BTb71ECQtqfAQ== Message-ID: <88f37900-5c8b-4606-9081-e9b72acb0941@kernel.org> Date: Wed, 18 Mar 2026 10:02:57 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/huge_memory: fix folio isn't locked in softleaf_to_folio() To: Jinjiang Tu , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, fengwei.yin@intel.com, baohua@kernel.org, ryan.roberts@arm.com, linux-mm@kvack.org Cc: wangkefeng.wang@huawei.com, sunnanyong@huawei.com References: <20260318012055.3593216-1-tujinjiang@huawei.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: DB8C120004 X-Stat-Signature: yjzctjap37s8x9tqfdp986qewx95tio1 X-HE-Tag: 1773824583-755457 X-HE-Meta: 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 V+46xgdk Yvy/IcSw+nyFUcMrenO61/0wgms2JNAF4I4cYQy5wKqxJVUpNfNiq4px8OpGHXUX/X/CF1CeIK4ZU1arQOknkZVt3Yj3UFu2ujhSA7E4Fb3es/+iafoZLzrfaZ/JoL/dqujUrUDjQnBWlMTuI2RR81seynB2+jHcZU2pfQx3NdzJfw/13woVrXefSKz/kxI+vSXHUFotxyWskjxOXTWXx1cC+s08DfyjjNhKLJk6cXqXNoPZYVhAHd9NvqOaawo6QGGP/ltRIFwwWUuRpCQtZlC72NeD13wOEy8F/LuPgic89c+ztqAgngODtrStxj9WZ4K8/FN/dBWpUYaw= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/18/26 02:20, 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. > > To fix it, add missing smp_rmb() if the softleaf entry is migration entry > in softleaf_to_folio() and softleaf_to_page(). > > Fixes: e9b61f19858a ("thp: reintroduce split_huge_page()") > Signed-off-by: Jinjiang Tu > --- > > Change since v1: > * update fix tag > * use helper softleaf_migration_entry_check() > > include/linux/leafops.h | 29 ++++++++++++++++++----------- > 1 file changed, 18 insertions(+), 11 deletions(-) > > diff --git a/include/linux/leafops.h b/include/linux/leafops.h > index a9ff94b744f2..c7dbc3fb8ab6 100644 > --- a/include/linux/leafops.h > +++ b/include/linux/leafops.h > @@ -363,6 +363,22 @@ static inline unsigned long softleaf_to_pfn(softleaf_t entry) > return swp_offset(entry) & SWP_PFN_MASK; > } > > +static inline void softleaf_migration_entry_check(softleaf_t entry, > + struct folio *folio) > +{ > + if (!softleaf_is_migration(entry)) > + return; > + > + /* See __split_folio_to_order() comment */ > + smp_rmb(); > + > + /* > + * Any use of migration entries may only occur while the > + * corresponding page is locked > + */ > + VM_WARN_ON_ONCE(!folio_test_locked(folio)); > +} > + > /** > * softleaf_to_page() - Obtains struct page for PFN encoded within leaf entry. > * @entry: Leaf entry, softleaf_has_pfn(@entry) must return true. > @@ -374,11 +390,7 @@ static inline struct page *softleaf_to_page(softleaf_t entry) > struct page *page = pfn_to_page(softleaf_to_pfn(entry)); > > VM_WARN_ON_ONCE(!softleaf_has_pfn(entry)); > - /* > - * Any use of migration entries may only occur while the > - * corresponding page is locked > - */ > - VM_WARN_ON_ONCE(softleaf_is_migration(entry) && !PageLocked(page)); > + softleaf_migration_entry_check(entry, page_folio(page)); It might be better to do if (softleaf_is_migration(entry)) softleaf_migration_entry_check(entry, page_folio(page)); Removing the softleaf_is_migration() check from softleaf_migration_entry_check(). Then, we don't do the unconditional page_folio() and don't call the function for non-migration-entries. With that LGTM. -- Cheers, David