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Tue, 10 Feb 2026 18:02:00 -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 07:31:48 +0530 X-Gm-Features: AZwV_QjXhIMFPf6jJ0SJ9mTsyFML5WJINl2nSTV_Le53QpuBO8uPBkMPoU2Q6Mw 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: rspam12 X-Stat-Signature: gfe8cq5d8o8fet4awhqmsafqd1upntp7 X-Rspamd-Queue-Id: 5E42F14000A X-Rspam-User: X-HE-Tag: 1770775321-875198 X-HE-Meta: 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 EJy65PFC t1SB3euGr+lPZGUXbvtAjbcXvZMkrxPoApZA9d+zoK1XOxA6LI5rLDpiME311UVGMNqz3DLYbMWpNsfz7G8dXBMcPqHUAAl1g8C333BhXSkKdQe+bsal1LyBQlriRBsOhP0iQ+1RW2gJEQnutEOv7GLFyuXXDXe1nZRm7t2o4YMrU+trJWLLNVKaeMbLvG73dqBuaVq/5+X9J0/o= 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 6:28=E2=80=AFAM Ackerley Tng wrote: > > Ackerley Tng writes: > > > "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. Shou= ld > >>> we backport AS_INACCESSIBLE there or could the fix for 5.15.199 just = be > >>> 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 retur= n > > false since secretmem has vma->vm_ops defined [1], so secretmem VMAs ar= e > > skipped. > > > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tr= ee/mm/khugepaged.c?h=3Dv5.15.199#n469 > > > > On 6.1.162, secretmem VMAs are skipped since secretmem VMAs are not > anonymous [2]. > > [2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree= /mm/huge_memory.c?h=3Dv6.1.162#n135 > > Same for 6.6.123 [3]. > > [3] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree= /mm/huge_memory.c?h=3Dv6.6.123#n125 > > It breaks in 6.12.69 [4]. > > [4] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree= /mm/huge_memory.c?h=3Dv6.12.69#n159 > > IIUC the patch that enabled khugepaged for secretmem is > > commit 7a81751fcdeb833acc858e59082688e3020bfe12 > Author: Zach O'Keefe > Date: Mon Sep 25 13:01:10 2023 -0700 > > mm/thp: fix "mm: thp: kill __transhuge_page_enabled()" > > ... > > @@ -132,12 +132,18 @@ bool hugepage_vma_check(struct vm_area_struct > *vma, unsigned long vm_flags, > !hugepage_flags_always()))) > return false; > > - /* Only regular file is valid */ > - if (!in_pf && file_thp_enabled(vma)) > - return true; > - > - if (!vma_is_anonymous(vma)) > + if (!vma_is_anonymous(vma)) { > + /* > + * Trust that ->huge_fault() handlers know what they are = doing > + * in fault path. > + */ > + if (((in_pf || smaps)) && vma->vm_ops->huge_fault) > + return true; > + /* Only regular file is valid in collapse path */ > + if (((!in_pf || smaps)) && file_thp_enabled(vma)) > + return true; > return false; > + } > > if (vma_is_temporary_stack(vma)) > return false; > > Because file_thp_enabled() would return true for secretmem. > Thanks for the analysis on stable kernels, Ackerley. So the fix only needs to target 6.12+ since that's where 7a81751fcdeb ("mm/thp: fix 'mm: thp: kill __transhuge_page_enabled()'") started routing secretmem through file_thp_enabled().