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 28072238159; Mon, 9 Feb 2026 10:38:19 +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=1770633500; cv=none; b=deBSbbE3IODptQnhpK3SWXh2zc/AvxWztP7Fub7Sp5rYh0tP0n8WUv71ldbnl2BJUdxvi0h4g/N4kk2f4A1+e+2N3IGK+rtbNP7y++N1mb+rxDmdBNxAFKmZznIYI0/xvumOhW7Lov4c3z56RknNicjdRTU1nRlf2rO/czutmL4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770633500; c=relaxed/simple; bh=PjFOZ2Yz7mO0UhUahvefnGZNcIR2YokkeQiLOGg5Z1U=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ryFHoXaQifp0+bu0cvyoS49SaSF3htN6yOgPHdju1R7+hEU1PMii9UEJEVDrnz09pdRriFXLc3C9DLgo/yiO5asb6xv3BEs0rNPUIULkqLMVLQ2IzrzTnxxRf+djccLoxfecha1NjB6XcuMqJGnlnLLLnLl46yjzOlTu0h2WCEE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KzEuNcQs; 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="KzEuNcQs" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B87AAC116C6; Mon, 9 Feb 2026 10:38:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770633499; bh=PjFOZ2Yz7mO0UhUahvefnGZNcIR2YokkeQiLOGg5Z1U=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=KzEuNcQs6j1nIvhTqD8J3QP5/G4Gdiz3j0txOgLx3WD3ac+GI2STE3v6Ge0i/iZ/D TcSFzdsrpG9NC6J0nar6uC5O3xaUvWKYkPM0IiLeJDR7HKusRzzbHsDO7S+XS/BmHb fFhTlzngjvzhpM5UG2DJx4hYhEvHl6VhoPGMYJvqGP8AAf682eoDvB5xPhzPU8evfA aBkWDC5TWwHlucC5IXs0XZgd0nTYgw005QVosp/l05dVnmg0nGscMB7LD787VSLYlb 4yQRU6kfgOR2JGParxz8Hm+GXmE6L/NS7VT2y0sUmFjZFCGmxIT2S9SS02mko6dMNR ob1HzUObjWFfw== Message-ID: <442d7ce8-0de3-4f5a-95ed-3be9bdaa7e47@kernel.org> Date: Mon, 9 Feb 2026 11:38:14 +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] KVM: guest_memfd: Disable VMA merging with VM_DONTEXPAND To: Ackerley Tng , Sean Christopherson Cc: syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, syzkaller-bugs@googlegroups.com, michael.roth@amd.com, vannapurve@google.com, kartikey406@gmail.com References: <697d115a.050a0220.1d61ec.0004.GAE@google.com> <20260204170144.2904483-1-ackerleytng@google.com> <16e5a36e-fff0-4a54-9c5c-a8e411659108@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 2/8/26 18:34, Ackerley Tng wrote: > Ackerley Tng writes: > >> >> [...snip...] >> >>> !thp_vma_allowable_order() must take care of that somehow down in >>> __thp_vma_allowable_orders(), by checking the file). >>> >>> Likely the file_thp_enabled() check is the culprit with >>> CONFIG_READ_ONLY_THP_FOR_FS? >>> >>> Maybe we need a flag to say "even not CONFIG_READ_ONLY_THP_FOR_FS". >>> >>> I wonder how we handle that for secretmem. Too late for me, going to bed :) >>> >> >> Let me look deeper into this. Thanks! >> > > I trimmed the repro to this: > > static void test_guest_memfd_repro(void) > { > struct kvm_vcpu *vcpu; > uint8_t *unaligned_mem; > struct kvm_vm *vm; > uint8_t *mem; > int fd; > > vm = __vm_create_shape_with_one_vcpu(VM_SHAPE_DEFAULT, &vcpu, 1, guest_code); > > fd = vm_create_guest_memfd(vm, SZ_2M * 2, GUEST_MEMFD_FLAG_MMAP | > GUEST_MEMFD_FLAG_INIT_SHARED); > > unaligned_mem = mmap(NULL, SZ_2M + SZ_2M, PROT_READ | PROT_WRITE, > MAP_FIXED | MAP_SHARED, fd, 0); > mem = align_ptr_up(unaligned_mem, SZ_2M); > TEST_ASSERT(((unsigned long)mem & (SZ_2M - 1)) == 0, "returned > address must be aligned to SZ_2M"); > > TEST_ASSERT_EQ(madvise(mem, SZ_2M, MADV_HUGEPAGE), 0); > > for (int i = 0; i < SZ_2M; i += SZ_4K) > READ_ONCE(mem[i]); > > TEST_ASSERT_EQ(madvise(mem, SZ_2M, MADV_COLLAPSE), 0); > > TEST_ASSERT_EQ(madvise(mem, SZ_2M, MADV_DONTNEED), 0); > > /* This triggers the WARNing. */ > READ_ONCE(mem[0]); > > munmap(unaligned_mem, SZ_2M * 2); > > close(fd); > kvm_vm_free(vm); > } > > And tried to replace the fd creation the secretmem equivalent > > fd = syscall(__NR_memfd_secret, 0); > TEST_ASSERT(fd >= 0, "Couldn't create secretmem fd."); > TEST_ASSERT_EQ(ftruncate(fd, SZ_2M * 2), 0); > > Should a guest_memfd selftest be added to cover this? > > MADV_COLLAPSE fails with EINVAL, but it does go through to > hpage_collapse_scan_file() -> collapse_file(), before failing because > when collapsing the page, copy_mc_highpage() returns > 0. Just what I suspected. :) Thanks for digging into the details! -- Cheers, David