From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 B34153B3888; Thu, 18 Jun 2026 11:26:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781782000; cv=none; b=nnNSnslL09ruMaiiFoamWokkEN0CdVaIM8uLSa8p6pRMm+Y88gBkFNxG5F36G4NgGthG8AceTLF0Vybf7Cg+Y6UmtYbeTkEzaF59jUjHkhJnqxtELxna0EPZajxHDCIjk7SnEoZAx4ZV0pT0fUfxeRo2tQeIcLE1MEqAHhFm+cI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781782000; c=relaxed/simple; bh=LcakeM4oMQyutQUdWBwBM3Vm2qpN4Zfb8HX1pR6lHsc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=WnsTomaa6GmpYH1s6JJqzgz9EzwdifP3c9ptk1gCOeQuhfyz5WS0tItJgzcUO23CxEB5O7QxHRqlGan+6cCU6x8efuYuNtNQF3twHAigjKfOdc8d4jj9IREf5dlazyX5jTZTy2MDave2KFRjP8/yDdJ2X6h/KjjvW+JdZImIlu4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RWOiyur8; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="RWOiyur8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 78D071F000E9; Thu, 18 Jun 2026 11:26:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781781999; bh=4QDK2jCIWPvZ2ONcm4xowx5WtNzU5+JH9ZsV8OFhnKA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=RWOiyur8C67wNqTpbgGN5qR7NuPJMtmXK7V875vdMJCXviAl5Uy50Hnd659YniuF6 YaveuThHh+nqLCw1lkNT7muJ8bSgMVTqtLKlA8b+MiM6XRtmCl2/BTEdx0/XJ6dPXx t9Nicf1spXrdiKz5258cvn1Yxfxp3/utXhjtM8lak9smXtSLTRztDJXOxoBa868Yq2 KqS9/xXeIMIMDHV2N3n4ki5J+TCpg8jAC+Y9+yJv2Ky29w7PuZaT9K53yT7eRx2RPd s1NypOU+Qxtp00E/WYoxwQbSO1W1GXyycjPuS9+FDmMkmXpWwR9SJkL/ulWU70uHQV pM2WziKqY2frw== Message-ID: <499650f7-8c9c-4e58-83d1-0bc26e23b949@kernel.org> Date: Thu, 18 Jun 2026 13:26:35 +0200 Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] KVM: Ignore MMU notifiers for guest_memfd-only memslots To: Sean Christopherson , sashiko-reviews@lists.linux.dev Cc: Alexandru Elisei , Marc Zyngier , kvm@vger.kernel.org, kvmarm@lists.linux.dev, Oliver Upton References: <20260615155244.183044-1-alexandru.elisei@arm.com> <20260615160901.9A1A61F000E9@smtp.kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/15/26 19:47, Sean Christopherson wrote: > On Mon, Jun 15, 2026, sashiko-bot@kernel.org wrote: >>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >>> --- a/virt/kvm/kvm_main.c >>> +++ b/virt/kvm/kvm_main.c >> [ ... ] >>> @@ -592,6 +592,10 @@ static __always_inline kvm_mn_ret_t kvm_handle_hva_range(struct kvm *kvm, >>> unsigned long hva_start, hva_end; >>> >>> slot = container_of(node, struct kvm_memory_slot, hva_node[slots->node_idx]); >>> + >>> + if (kvm_slot_has_gmem(slot) && kvm_memslot_is_gmem_only(slot)) >>> + continue; >>> + >> >> [Severity: Critical] >> Does this change inadvertently introduce a regression in the pfncache retry >> protocol? >> >> Looking at the pfncache framework, it maps guest memory into kernel space and >> explicitly drops the page reference after mapping it: >> >> virt/kvm/pfncache.c:hva_to_pfn_retry() { >> ... >> kvm_release_page_clean(page); >> ... >> } >> >> It appears to rely entirely on KVM's MMU notifiers (kvm->mmu_invalidate_seq) >> to invalidate the cache when the page is unmapped by the host. >> >> If a VMM defines a guest_memfd-backed memslot with KVM_MEMSLOT_GMEM_ONLY >> but still provides a valid anonymous user mapping as its userspace_addr, >> could this regression lead to a use-after-free? > > Sadly, yes. To land this, we would need to first teach the gfn_to_pfn_cache code > to be able to pull directly from guest_memfd. I forget if anyone is working on > that. For completeness, I think this is what you are looking for: https://lore.kernel.org/r/20260420154720.29012-1-itazur@amazon.com -- Cheers, David