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Tue, 10 Feb 2026 15:00:45 -0800 (PST) Received: from 176938342045 named unknown by gmailapi.google.com with HTTPREST; Tue, 10 Feb 2026 15:00:44 -0800 Received: from 176938342045 named unknown by gmailapi.google.com with HTTPREST; Tue, 10 Feb 2026 15:00:44 -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 15:00:44 -0800 X-Gm-Features: AZwV_QiyL3s3BKXXhdK7iIwoIbxPAJAsEDXhkwYpXpmL4-mRW4CWWWKmYNrmdsM 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: rspam03 X-Rspamd-Queue-Id: 88C0D1A001C X-Stat-Signature: jp5iaaduffa9xdg1b3hacr6hci87jgrf X-Rspam-User: X-HE-Tag: 1770764446-39089 X-HE-Meta: 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 gGKZFwOT TjOjjb4FA/Ps8yxfuly16ziVTKXTVLdO3t0MfwlQC+32bLLq+C4VqJ1qHYhaYhJHT9cbAFTU6ECrMqQmqkKe2VI75sUQA62IIG3qGkzHl+dRcLlgECqjo+NbYHhQnI81MRVky5Nuu9oPxvg/BuKEzmmbwvj1fy4io7IoAYZ8sZRqRp5NPPMmaNzJijBstLVt1IKvsbgVVFmWtC9Z+ereBIrFvJ/wL9i+HVPDYKMB0qoaOGpnBgFL/YHYRiDlVoZUEne6suDrPcdd+9JVpzHJUoCgdPYeuXU7VNEbTEooDlh7ReWlzSayNRpdQlUcx3L+yvMT8G6ZOI1yU2suUrQ8DDTGxOfKNjgURn4qqtfogyMYbuIbj6UBLqt3RHrgBBg0kH2QVGI1eT1uIlaeIrwp3AXSyAwOJYtUSILFpVc/OyhKZit8/a7oKmnyhR+btV2ZshS1wEWcvT3VfOc2AlgqW/9lWacJ0A8nthSMZRzoc7lfuRLQ= 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: "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 >> >>> >>> 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 = 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?) >> >> Regarding the degradation of filesystems that don't support large folios >> yet: Do you mean having the collapse function respect AS_FOLIO_ORDER_MAX >> would disable collapsing for filesystems that actually want pages to be >> collapsed, but don't update max folio order and hence appear to not >> support large folios yet? >> >> What about a check like this instead >> >> if (!mapping_large_folio_support()) >> return false; > > That would essentially disable CONFIG_READ_ONLY_THP_FOR_FS (support for > THP before filesystems started supporting large folios officially), no? > I think I get what you mean now. I was thinking to also update the filesystems to specify AS_FOLIO_ORDER_MAX, but I think that is better separated out as a different patch series, and this should focus on just fixing the bug. > -- > Cheers, > > David