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Tue, 10 Feb 2026 17:59:35 -0800 (PST) MIME-Version: 1.0 References: <20260209033558.22943-1-kartikey406@gmail.com> <0d9cada8-7148-4a5c-a09d-120ef54559d7@kernel.org> <4ed1b111-f2f1-4f89-9308-fdd9d706ca37@kernel.org> <8f188d73-fc97-414b-bdaa-e72032b2bf82@kernel.org> In-Reply-To: From: Deepanshu Kartikey Date: Wed, 11 Feb 2026 07:29:23 +0530 X-Gm-Features: AZwV_Qg3e3DLlPtLr0FMRkXA-24Zu6q8lzeHImpYKVgBS09u4-NVv29V3PEUAUE Message-ID: Subject: Re: [PATCH] mm: thp: Deny THP for guest_memfd and secretmem in file_thp_enabled() To: Ackerley Tng Cc: "David Hildenbrand (Arm)" , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, seanjc@google.com, pbonzini@redhat.com, michael.roth@amd.com, vannapurve@google.com, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 4EEB1C0008 X-Stat-Signature: dcahc3gnda5p7hk6g1nmnfdtcwcw9m6o X-Rspam-User: X-HE-Tag: 1770775176-91555 X-HE-Meta: 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 Yr+f3FiP cZijBqCkqOSuOyKINDGFSbiaNyxqCOFa77j2l+3ZUnjvlyvUhlg1Y23AzFBL5QfEWJrO0dkdeL6Q+C6oVF7vByh+/eySrBrOI3MBr4H0+ZgcHFLmzQl6SolG0OgMFu1jbKEIftqzibdlJI6kdlxDPShznWh8ux9nl/RjQAWLM/EG50WepEwv9n2ZaL+EunRaN+GH/z5DaKa1QCfpNTVDuO8EUe3aWGoQDgXXuuKLsIga0KjbQ1mV+u92m+E1ogX/9H1DU10znra5Puz533CJn7mjPbF8lExjSfrPbZFC4TOSp4lNVJwe8Zrcj8EAyFE27NaoDmNjCdQwKiIDKg4rEQFZ7dzokAaCo673zC4P5n+KGAJmO0CLpfH3M6PzyjWlgLMzsEY+MoQi139SJnrj1cItFl8mqKTy0AoL5LL5dcB4CE5cioxhbNZ4jdtikdlgUwg7TWeFB1k54fKBaWfE/L0Udc9M/bw0/HQkqmqgFBQAjGFt4cMx+BgLbvM2DYcvXp3T8/kw8itOFz5APkm8qlUhiGDnexRHYN78Wv8C+lIErs0dqk70lNgg5bO73yrv8e/BhFSmTxo3Sb8XoMPS0C8Y+p87BQM0QXfypPQ39jspx2HU9p0OX0MgTc4VPuH8HhG0NP5NvNQAWu+M= 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: List-Subscribe: List-Unsubscribe: On Wed, Feb 11, 2026 at 4:30=E2=80=AFAM Ackerley Tng wrote: > > "David Hildenbrand (Arm)" writes: > > >>> BUT, something just occurred to me. > >>> > >>> We added the mc-handling in > >>> > >>> commit 98c76c9f1ef7599b39bfd4bd99b8a760d4a8cd3b > >>> Author: Jiaqi Yan > >>> Date: Wed Mar 29 08:11:19 2023 -0700 > >>> > >>> mm/khugepaged: recover from poisoned anonymous memory > >>> > >>> .. > >>> > >>> So I assume kernels before that would crash when collapsing? > >>> > >>> Looking at 5.15.199, it does not contain 98c76c9f1e [1]. > >>> > >>> So I suspect we need a fix+stable backport. > >>> > >>> Who volunteers to try a secretmem reproducer on a stable kernel? :) > >>> > >> > >> I could give this a shot. 5.15.199 doesn't have AS_INACCESSIBLE. Shoul= d > >> we backport AS_INACCESSIBLE there or could the fix for 5.15.199 just b= e > >> special-casing secretmem like you suggested below? > > > > Yes. If there is no guest_memfd we wouldn't need it. > > > > Seems like on 5.15.199 there's a hugepage_vma_check(), which will return > false since secretmem has vma->vm_ops defined [1], so secretmem VMAs are > skipped. > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree= /mm/khugepaged.c?h=3Dv5.15.199#n469 > > >> > >>> > >>> The following is a bit nasty as well but should do the trick until we= rip > >>> out the CONFIG_READ_ONLY_THP_FOR_FS stuff. > >>> > >>> > >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c > >>> index 03886d4ccecc..4ac1cb36b861 100644 > >>> --- a/mm/huge_memory.c > >>> +++ b/mm/huge_memory.c > >>> @@ -40,6 +40,7 @@ > >>> #include > >>> #include > >>> #include > >>> +#include > >>> > >>> #include > >>> #include "internal.h" > >>> @@ -94,6 +95,10 @@ static inline bool file_thp_enabled(struct vm_area= _struct *vma) > >>> > >>> inode =3D file_inode(vma->vm_file); > >>> > >>> + if (mapping_inaccessible(inode->i_mapping) || > >>> + secretmem_mapping(inode->i_mapping)) > >>> + return false; > >>> + > > Regarding checking mapping, is there any chance of racing with inode > release? (Might the mapping be freed?) > > >> I don't think so. file_thp_enabled() is called from __thp_vma_allowable_orders(), which is reached via khugepaged, MADV_COLLAPSE, or page faults. All these paths hold mmap_lock and operate on a valid VMA. The VMA holds a reference to the file (vma->vm_file), which holds a reference on the inode, so the inode and its mapping cannot be freed while we are checking it..