From nobody Tue Feb 10 20:47:06 2026 Received: from mail-oo1-f72.google.com (mail-oo1-f72.google.com [209.85.161.72]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3170127A10F for ; Mon, 9 Feb 2026 01:55:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.161.72 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770602154; cv=none; b=GgrREmh+iNoziovBVf7W5VLWa0qJv6uEZDISH+/nFPxWnM7SXgTuKRDx2UPa+d0rivZ6UiGXJXZGHjE92qxitc+Te1PhP0rqT+pm093TNQ0qXlGigd+oZcsKPSLP9Y8SnfPPB95U0MIzD5jDxafqCMHBwl5ikPGGE+wkv9BlazA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770602154; c=relaxed/simple; bh=0J2WunV3Zj076Zi8m0nsn9cEjVuP4udrYjiAFHwLPfQ=; h=MIME-Version:Date:In-Reply-To:Message-ID:Subject:From:To: Content-Type; b=lIEKbuDnnL/lO1y9wvfN5iNNLbe4s+DcSjC7O3O5WR9goLX7Shx+hNPUiKP08A6DZJL3UwbWomovpRlEANPV5YsQFZErDEwiVtSgCcgLM8gLgsr/ERZ+/wk4OcRWE9Hi71moQmjbfawAuBAWXJtLzN/BJdRDSAxwU1TwxrdZOsw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com; arc=none smtp.client-ip=209.85.161.72 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com Received: by mail-oo1-f72.google.com with SMTP id 006d021491bc7-6630d58662aso21650332eaf.0 for ; Sun, 08 Feb 2026 17:55:53 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1770602153; x=1771206953; h=to:from:subject:message-id:in-reply-to:date:mime-version :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=rgIQYa4tqbqOAEONFp2ETS6TbMpoeymt4GKGkdEJ690=; b=AgWQsv70yGHwaTKf7v9NmqQEdL7fyEv/71BYrLHm6iZZ+tpv/6e+0++bZNke3jgogV ydAaKQBXiMTTk34RO5Z8pIsrh8TBF6Gut8HizgDN42Px52+d/Qk60MZgjgxHDbJSXHrO Y8stf7QyvXBaG8FKbreoOBaMzwM0d6EMe+o5oPk8kZVrrv+/7+xmbKWTPcWIRxGEjZis lwkurvxHc7hmqu1CDli/B+NeJU/Sbqn/k/PamUfJlHvqyypTUqbYBHlW00Szj2Yq29TX fGFueEnukVoBCD9YS8p2ZVkssmJcQLTo3f1TalWjlYnM1DOUXvCyUE0j6CHnMM6MyEj4 5bDg== X-Gm-Message-State: AOJu0Ywj6nQI2xga5XWwLaxhD8NJ1nM9zkSKSToWSRse7c+K8OE2bopB urkB0NipirBGTPLnNVAqzk7UGWIKX+00S15QDfWOTzDaf6CmRYemiBnAvcE1d4znc3tfhaF0RDy RRTjQ0urDwg0daZOwKkcIIfF5H27mtjS0/ekwMO9ISwgw5yiktHnxpGvrfQw= Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Received: by 2002:a05:6820:3088:b0:662:f61e:759d with SMTP id 006d021491bc7-66d0c666b89mr4711585eaf.62.1770602153200; Sun, 08 Feb 2026 17:55:53 -0800 (PST) Date: Sun, 08 Feb 2026 17:55:53 -0800 In-Reply-To: <697d115a.050a0220.1d61ec.0004.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <69893ea9.050a0220.3b3015.0064.GAE@google.com> Subject: Forwarded: [PATCH] KVM: guest_memfd: Prevent THP collapse of guest_memfd pages From: syzbot To: linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" For archival purposes, forwarding an incoming command email to linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com. *** Subject: [PATCH] KVM: guest_memfd: Prevent THP collapse of guest_memfd pages Author: kartikey406@gmail.com #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git= master guest_memfd fault handler kvm_gmem_fault_user_mapping() does not support large folios and warns via WARN_ON_ONCE(folio_test_large(folio)). When a guest_memfd mapping has VM_HUGEPAGE set via madvise(MADV_HUGEPAGE), khugepaged or MADV_COLLAPSE can collapse small pages into a large folio in the page cache. This happens because file_thp_enabled() incorrectly returns true for guest_memfd inodes when CONFIG_READ_ONLY_THP_FOR_FS is enabled. A subsequent page fault finds the large folio and triggers the warning. Fix this by setting VM_NO_KHUGEPAGED on the VMA in kvm_gmem_mmap(). This causes __thp_vma_allowable_orders() to reject THP early for both MADV_COLLAPSE and khugepaged. The page fault path is unaffected since guest_memfd does not define a huge_fault handler. Reported-by: syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D33a04338019ac7e43a44 Signed-off-by: Deepanshu Kartikey --- virt/kvm/guest_memfd.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index fdaea3422c30..94ac360afe79 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -474,12 +474,13 @@ static int kvm_gmem_mmap(struct file *file, struct vm= _area_struct *vma) { if (!kvm_gmem_supports_mmap(file_inode(file))) return -ENODEV; - +=09 if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) !=3D (VM_SHARED | VM_MAYSHARE)) { return -EINVAL; } =20 + vm_flags_set(vma, VM_NO_KHUGEPAGED); vma->vm_ops =3D &kvm_gmem_vm_ops; =20 return 0; --=20 2.43.0