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Wed, 11 Feb 2026 08:16:07 -0800 (PST) Received: from 176938342045 named unknown by gmailapi.google.com with HTTPREST; Wed, 11 Feb 2026 08:16:06 -0800 Received: from 176938342045 named unknown by gmailapi.google.com with HTTPREST; Wed, 11 Feb 2026 08:16:06 -0800 From: Ackerley Tng In-Reply-To: <5759bfba-f235-4b2d-bb30-919dcdfe7b2c@kernel.org> 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> <5759bfba-f235-4b2d-bb30-919dcdfe7b2c@kernel.org> MIME-Version: 1.0 Date: Wed, 11 Feb 2026 08:16:06 -0800 X-Gm-Features: AZwV_QgQ7r_3lH9Aj7yhn8j8us0bHR_cQtnixpMPdHLE2O42Gfq5J2j8Tc-MA1I 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-Queue-Id: 0D613180009 X-Stat-Signature: 1hb6az8x4if7e9tdxzhdb7y8umq1t7h6 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1770826568-911902 X-HE-Meta: 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 7mgT7pms Vwb4Z+vf6LtIlIfuiXZjRE4O0jSiEeJJsPOU21Lz39UF4AIGKZSTV5CAFjfvFyD+odAzh8t3Kh1zBeS4Pmier9jT+YuCP+dpPWeG2l21ixrhREo4GoMOJlYwlDX2dLdEVBg4Z 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: > On 2/11/26 01:58, Ackerley Tng wrote: >> Ackerley Tng writes: >> >>> "David Hildenbrand (Arm)" writes: >>> >>>> >>>> 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]. > > > Do you have a reproducer? If so, which behavior does it trigger? > > I would assume that we would suddenly have secretmem pages (THP) that > have a directmap. Or some page copy would crash the kernel. > Is there a good way to verify from userspace that the directmap hasn't been restored? Should I use CONFIG_PTDUMP_DEBUGFS? > -- > Cheers, > > David