From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 44DF93451A6 for ; Wed, 11 Feb 2026 16:45:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770828339; cv=none; b=OvMC0GOgjmyxJuvsOvcwrH3DqIG01X6vELm1s32nsVN2ihoFpDict1alYh8iToQS29W0yEgkkZ20sMH2iymbv5UXGh0kjprWqmN32lCXDhXT6DWOik/F3aF9diGsvqAbK5cHIgp2CU19Vs0x9lFMO4HmlIMFe3jX20a8RxojhZ0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770828339; c=relaxed/simple; bh=ptfH5xoqmieZP4iCxFCvPxbGMO4BUbpqj9XhdYwlR9A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=CTiRkGH1aBHv87DW/wx7h+sigqfec77ciIA9LSL3ZktbFDEhwR+30qijI8p49CYEcmEfasMDepQC7Mbe3ifnNXw3utkqaMQ8ZOoU+DOK5e4dBU13zIQYl/Uo236kRKR8wHB76p3Iau+99j2ruJdaBB+/YWktUerW8gKjW1mdH0s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pk4QdTTS; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="pk4QdTTS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 437EEC4CEF7; Wed, 11 Feb 2026 16:45:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770828338; bh=ptfH5xoqmieZP4iCxFCvPxbGMO4BUbpqj9XhdYwlR9A=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=pk4QdTTSql2H+vUPzMiVYTA1JaIOQqoGNh7f/wwtMJeYLY90MlFXBFhj46bvXc3bJ YyS21HWNl+M5Ttedla5BcyoN3buJ8CXGRmeKzHAMd+QTACA2dqv4pXQUhWMUGc6Ri3 5KNIb8FEztaP2N6IPxdJkByDItclGB4Re/iMJnotgYwN+xYZtex691b9J1vFyKpYPn p2128rlGoXOIabfUi61qyyORkGmGQGCUbwAmNxE2nnR8BYOc5rqYVH8nnVs+R1zNbB AI4ZnVAlfTUh6N4jDMKqV0cErfDgOd1kepVXgmotOCQdtJmu64Q/lWgzfVKpVB44aM Avir8haEx5nQg== Message-ID: <5eb7aae7-f642-43d2-810b-d7afd867d665@kernel.org> Date: Wed, 11 Feb 2026 17:45:30 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: thp: Deny THP for guest_memfd and secretmem in file_thp_enabled() To: Ackerley Tng , 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, Fangrui Song 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> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/11/26 16:38, Ackerley Tng wrote: > "David Hildenbrand (Arm)" writes: > >> On 2/11/26 00:00, Ackerley Tng wrote: >>> "David Hildenbrand (Arm)" writes: >>> >>> >>> 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. >> >> Are you sure? We check for CONFIG_READ_ONLY_THP_FOR_FS before that: >> > > Ah... I was working on a reproducer then I realized 5.15 doesn't have > MADV_COLLAPSE, then I tried to hack in an ioctl to trigger > khugepaged. That turned out to be awkward but it got me to look at > hugepage_vma_check(), and then I went down the rabbit hole to keep > looking for the similar check function throughout the other stable > kernels... and amongst all of that forgot that > CONFIG_READ_ONLY_THP_FOR_FS was unset :( > > You're probably right about VM_EXEC. > > Here's the reproducer for 6.12, I put this in > tools/testing/selftests/mm/memfd_secret.c and called repro() from > main(). This time I enabled CONFIG_READ_ONLY_THP_FOR_FS :). > > void repro(void) > { > uint8_t *mem; > int ret; > int fd; > int i; > > printf("%d triggering secretmem\n", __LINE__); > > fd = memfd_secret(0); > if (fd < 0) { > if (errno == ENOSYS) > ksft_exit_skip("memfd_secret is not supported\n"); > else > ksft_exit_fail_msg("memfd_secret failed: %s\n", > strerror(errno)); > } > > if (ftruncate(fd, SZ_2M)) > ksft_exit_fail_msg("ftruncate failed: %s\n", strerror(errno)); > > #define ALIGNED_ADDRESS ((void*)0x400000000UL) > > mem = mmap(ALIGNED_ADDRESS, SZ_2M, PROT_READ | PROT_WRITE, MAP_FIXED > | MAP_SHARED, fd, 0); > if (mem != ALIGNED_ADDRESS) > ksft_exit_fail_msg("Couldn't allocate memory\n"); > > ret = madvise(mem, SZ_2M, MADV_HUGEPAGE); > if (ret) > ksft_exit_fail_msg("MADV_HUGEPAGE failed mem=%p ret=%d errno=%d\n", > mem, ret, errno); > > #define READ_ONCE(x) (*(volatile typeof(x) *) &(x)) > for (i = 0; i < SZ_2M; i += getpagesize()) > READ_ONCE(mem[i]); > > ret = madvise(mem, SZ_2M, MADV_COLLAPSE); > if (ret) > ksft_exit_fail_msg("MADV_COLLAPSE failed ret=%d errno=%d\n", ret, errno); > > munmap(mem, SZ_2M); > close(fd); > } > > This reproducer gets us to madvise_collapse() -> > hpage_collapse_scan_file() -> collapse_file(), and copy_mc_highpage() > fails because copy_mc_to_kernel() returns 4096. > > memory_failure_queue() causes this to be printed on the console > > [ 1068.322578] Memory failure: 0x106d96f: recovery action for clean > unevictable LRU page: Recovered > > No crash :) Is a crash the requirement for a backport to stable kernels? I'd say being able to trigger that is sufficient. There is no real memory failure :) -- Cheers, David