From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oi1-f197.google.com (mail-oi1-f197.google.com [209.85.167.197]) (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 0158338D404 for ; Tue, 15 Sep 2026 01:38:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.167.197 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789436320; cv=none; b=p5xN8yTUm3ZY5H32Zl6iHOIMe/we4yy5oorZryWcbNc4ecASW5l5fQJ23nRW5viHma/maiyyioatGrvkGvvv6pVThF1e4dv8ECdezBG/jJKMvKOgTzlP6vI51UGzUHr9hk8MasWtv0BBIbOfr9atPPKLZmyn0HHTkLNJPM5U0Kk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789436320; c=relaxed/simple; bh=kTHPOCcnlCDoudbJ0oNJ2FysjhAWiOkueDhxlW+QOCE=; h=MIME-Version:Date:In-Reply-To:Message-ID:Subject:From:To: Content-Type; b=T/87kRWAEBbeQ5/bs8GiLGi7Rxi3MXkJvkJbioM4zH3hlqAVsh0z6PpHkiBwIDqxYZhzP1z34WgXpc6i/a1nMnWjoFBaPLn7WbF1Ni4X/9b2/zc0wDYXfIeBzeA8k1WlY4Eyo0l/GmBS8oAgHQykVK96CQ/+3kskr8BgA76yUi8= 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=209.85.167.197 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-oi1-f197.google.com with SMTP id 5614622812f47-4959c49e054so3129669b6e.3 for ; Mon, 14 Sep 2026 18:38:38 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1789436318; x=1790041118; h=content-type:to:from:subject:message-id:in-reply-to:date :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to:content-type; bh=0jU5rdMwleJVbQ8DpwiGkG8NG+1SZ88on5KfKsWqEBk=; b=jVfwn0b+iTs8cUaLQ1/LruRBuJgPqiaHMy1kDOKKNM2+aIzhn1hoZIjU3wIZgjRD+H B2O+66aDeVKwd5HCaJfuEteULhrldiSMARkYLYUZsqClBwAVd5HhKcFGvHAEv5xLwSTY k3O1mjmm2KxlKDnLXpFvymS0+IMIte06MvDw5TEa2jIUiO6r9fiZebesuC1AwtlLpVuk 4FmiqEYd8XxbVEXegBCjEfpRFclpjMXDYPRtH8EzghcfW/0ZImOCBkt7YUdvaaxJ+cDg n7ElS9wA+JHzK/ExCyXffBVaS22QsAVC2KfRjiMZcZr997LgAgFckYz8qDq5YKklhZFQ Iaow== X-Gm-Message-State: AFuF++l+C/hBSBxE2P5i2o1iy8BGfJWN5fl6qNqN3RseXT0xKO662L5D +BYkX3MOQUA6snXZlubFoLI5ysmP4dwbzCF3J569LLCs4schLJIQLdKYLds9IC6iXK1W9jOxxJy 3q6aQo9ISR/N5fTJqh/Ds5Svl7x7BXQDqryDiFUYhP8BAQwh7xzuDYuyEaZg= Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Received: by 2002:a05:6820:1609:b0:6b3:6236:6fa with SMTP id 006d021491bc7-6c53f050dd0mr2782777eaf.21.1789436317932; Mon, 14 Sep 2026 18:38:37 -0700 (PDT) Date: Mon, 14 Sep 2026 18:38:37 -0700 In-Reply-To: <6aa42297.f2639fcc.29487d.002f.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <6aa8a19d.4c28b7d0.c1bba.0029.GAE@google.com> Subject: Forwarded: [PATCH] INFO: task hung in kvm_gmem_release (2) From: syzbot To: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" For archival purposes, forwarding an incoming command email to linux-kernel@vger.kernel.org. *** Subject: [PATCH] INFO: task hung in kvm_gmem_release (2) Author: jchuang26@m.fudan.edu.cn #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master Reported-by: syzbot+ab6273c58262b9de56d9@syzkaller.appspotmail.com diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 65eb26a05..8843dc35c 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2534,6 +2534,52 @@ static bool kvm_pre_set_memory_attributes(struct kvm *kvm, return kvm_arch_pre_set_memory_attributes(kvm, range); } +/* + * Reserve or store @entry for every gfn in [@start, @end) that is backed by + * a memslot. + * + * Only gfns that are backed by a memslot are tracked; attributes for any + * other gfn are meaningless, as such gfns cannot be mapped into the guest. + * Walking the entire, user-controlled range instead would let userspace + * force KVM to hold slots_lock for an unbounded amount of time while + * allocating an unbounded amount of memory. That can starve other + * slots_lock users, e.g. kvm_gmem_release() can get stuck waiting for + * slots_lock and trigger a hung task splat. + */ +static int kvm_set_mem_attributes_walk(struct kvm *kvm, gfn_t start, gfn_t end, + void *entry, bool store) +{ + int as_id; + + for (as_id = 0; as_id < kvm_arch_nr_memslot_as_ids(kvm); as_id++) { + struct kvm_memslots *slots = __kvm_memslots(kvm, as_id); + struct kvm_memslot_iter iter; + + kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) { + gfn_t gfn = max(start, iter.slot->base_gfn); + gfn_t gfn_end = min(end, iter.slot->base_gfn + iter.slot->npages); + + for (; gfn < gfn_end; gfn++) { + int r; + + if (store) + r = xa_err(xa_store(&kvm->mem_attr_array, + gfn, entry, + GFP_KERNEL_ACCOUNT)); + else + r = xa_reserve(&kvm->mem_attr_array, + gfn, GFP_KERNEL_ACCOUNT); + if (r) + return r; + + cond_resched(); + } + } + } + + return 0; +} + /* Set @attributes for the gfn range [@start, @end). */ static int kvm_vm_set_mem_attributes(struct kvm *kvm, gfn_t start, gfn_t end, unsigned long attributes) @@ -2555,7 +2601,6 @@ static int kvm_vm_set_mem_attributes(struct kvm *kvm, gfn_t start, gfn_t end, .on_lock = kvm_mmu_invalidate_end, .may_block = true, }; - unsigned long i; void *entry; int r = 0; @@ -2571,24 +2616,17 @@ static int kvm_vm_set_mem_attributes(struct kvm *kvm, gfn_t start, gfn_t end, /* * Reserve memory ahead of time to avoid having to deal with failures - * partway through setting the new attributes. + * partway through setting the new attributes. Note, only gfns that + * are backed by a memslot are reserved, see the walker. */ - for (i = start; i < end; i++) { - r = xa_reserve(&kvm->mem_attr_array, i, GFP_KERNEL_ACCOUNT); - if (r) - goto out_unlock; - - cond_resched(); - } + r = kvm_set_mem_attributes_walk(kvm, start, end, entry, false); + if (r) + goto out_unlock; kvm_handle_gfn_range(kvm, &pre_set_range); - for (i = start; i < end; i++) { - r = xa_err(xa_store(&kvm->mem_attr_array, i, entry, - GFP_KERNEL_ACCOUNT)); - KVM_BUG_ON(r, kvm); - cond_resched(); - } + r = kvm_set_mem_attributes_walk(kvm, start, end, entry, true); + KVM_BUG_ON(r, kvm); kvm_handle_gfn_range(kvm, &post_set_range);