From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794590840; b=pHJ05LvW2LgTgMcZYFLhRDMHlOxGgt7whEJjaVcU9XVobzPcNatg8wMFo/+3Dl5yCLRf pDcu9imSpSxohhUoyafsGgzstKCBHyHxaCLfLWOMxZCAg8iswM57rWDygcS7qtgpW0cK8 vd5nt1G27L7f5N4yHS4LlqdR8IFPfIrQwcQbaNElRHabBzlh1iK2saf0+1afS0tw8C5LR rtm+FZP1yviqMWWp7fV9QKffUDpE85Ekqe++ZqxCFHafz3NoF3CH4bRJxwxortSWNXCj+ q1gZajQVH9BC+hqUKFAauq4GG+IDo1bShs4DLt9KkWkdrKovJiPokIlfL73g98hDEeg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794590840; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=RiHQnc+4HdckSlooHJwIc5eIKebvXU6eZevewlxEE4U=; b=rSjdms4Yys1zCaXygHK7KfjUC9tmyKlNTwA6AhKk20/CLcHJqpQ0rr63O3TepkKijPeO Q+L4Vf+HDtcX4qoStJR7N7K5lkSVpoHcAyOQfkl40wmQssFLyvccwEvK7OefFoq1VdVGU ZLIVa16vM7lcoOIda/P1IEsymLhxGJbhBuHCfkm7Y9JFHi+NHIQkg/VkQpWHMw9NBc8oA Hm5qrdAwOV7oZ9TRa26HM+ubGCOdjMtIEDsm37YmGSOh8fCnk6Z+Im2GtMfuBaauAHGF+ VWrfa74oXZLNJndijz7wjvNzNiO1E6kNUi05kXmGy2R7JE4w5YCZVMFvf/Yb9Rmv7mA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=cAJj7BxC; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D0880607E07B; Fri, 13 Nov 2026 17:27:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=cAJj7BxC Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7BEAB1F000C4; Fri, 13 Nov 2026 17:27:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794590840; bh=RiHQnc+4HdckSlooHJwIc5eIKebvXU6eZevewlxEE4U=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=cAJj7BxCWOHkfQjbdHnAO1ARbHHypZY1EA2j6o4JVvEWE8dyPdgr9i42JnIOvMSfR qV05fHFrieKjxwQBBJCd8YhhbP0LNE9cCQfetPWEzekOSjCz8wC/0z0w70XdZHKy7v DCSzYgy+ple7UNU8TdY+tfqDXHA2i5gzgskbiaIc= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "David Hildenbrand (Arm)" , Sean Christopherson , Sasha Levin Subject: [PATCH 6.12 042/670] KVM: Only bind memslot to guest_memfd instance for CREATE operations Date: Fri, 13 Nov 2026 10:43:26 -0500 Message-ID: <20261113153812.591248679@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261113153811.177190860@linuxfoundation.org> References: <20261113153811.177190860@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sean Christopherson [ Upstream commit 513333a5546017da2a4a6173bfb70372f83733b3 ] For additional defense-in-depth, and to avoid having to handle impossible unwind scenarios when binding to a memslot fails, bind a memslot to a gmem instance only for CREATE operations, i.e. don't attempt to establish a binding for MOVE and FLAGS_ONLY operations. And when FLAGS_ONLY operations are eventually supported (this is currently all dead code), creating a new binding would be incorrect; KVM instead needs to do a 1:1 replacement of the existing binding, i.e. FLAGS_ONLY will need its own dedicated handling. Update the relevant TODO to make a better guess as to what needs to be done to support toggling dirty logging for guest_memfd memslots. Because it's dead code, no functional change intended. Cc: stable@vger.kernel.org Reviewed-by: David Hildenbrand (Arm) Link: https://patch.msgid.link/20260922001332.1121266-4-seanjc@google.com Signed-off-by: Sean Christopherson Signed-off-by: Sasha Levin --- virt/kvm/kvm_main.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 0d017f75c5a11..c574cd2f4f722 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1740,10 +1740,10 @@ static void kvm_commit_memory_region(struct kvm *kvm, kvm_destroy_dirty_bitmap(old); /* - * Unbind the guest_memfd instance as needed; the @new slot has - * already created its own binding. TODO: Drop the WARN when - * dirty logging guest_memfd memslots is supported. Until then, - * flags-only changes on guest_memfd slots should be impossible. + * TODO: Drop the WARN and do the unbind() call only for MOVE + * when dirty logging guest_memfd memslots is supported. Until + * then, flags-only changes on guest_memfd slots should also be + * impossible; unbind the old memslot for defense-in-depth. */ if (WARN_ON_ONCE(old->flags & KVM_MEM_GUEST_MEMFD)) kvm_gmem_unbind(old); @@ -2102,7 +2102,7 @@ int __kvm_set_memory_region(struct kvm *kvm, new->npages = npages; new->flags = mem->flags; new->userspace_addr = mem->userspace_addr; - if (mem->flags & KVM_MEM_GUEST_MEMFD) { + if (change == KVM_MR_CREATE && (mem->flags & KVM_MEM_GUEST_MEMFD)) { r = kvm_gmem_bind(kvm, new, mem->guest_memfd, mem->guest_memfd_offset); if (r) goto out; @@ -2115,7 +2115,7 @@ int __kvm_set_memory_region(struct kvm *kvm, return 0; out_unbind: - if (mem->flags & KVM_MEM_GUEST_MEMFD) + if (change == KVM_MR_CREATE && (mem->flags & KVM_MEM_GUEST_MEMFD)) kvm_gmem_unbind(new); out: kfree(new); -- 2.53.0