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Tue, 10 Feb 2026 16:58:09 -0800 (PST) Received: from 176938342045 named unknown by gmailapi.google.com with HTTPREST; Tue, 10 Feb 2026 16:58:08 -0800 Received: from 176938342045 named unknown by gmailapi.google.com with HTTPREST; Tue, 10 Feb 2026 16:58:08 -0800 From: Ackerley Tng In-Reply-To: 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> MIME-Version: 1.0 Date: Tue, 10 Feb 2026 16:58:08 -0800 X-Gm-Features: AZwV_QgxDeulAecHpn01PDRcqPsvuaGcOCbNfwjGI7BfIAkpouXJ6tRzoK3ZvZA Message-ID: Subject: Re: [PATCH] mm: thp: Deny THP for guest_memfd and secretmem in file_thp_enabled() To: "David Hildenbrand (Arm)" , Deepanshu Kartikey Cc: 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" X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: C9D1818000E X-Stat-Signature: zxkchbxorr4m3jdwqs87pkfpbocr6wrp X-Rspam-User: X-HE-Tag: 1770771490-563606 X-HE-Meta: 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 k1t41K0+ 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 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: 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. Should >>> 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 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=v5.15.199#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=v6.1.162#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=v6.6.123#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=v6.12.69#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. >>> >>>> >>>> >>>> [...snip...] >>>>