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=1793819830; b=fJGzaHPAcMtxM5IX3UOiFcPdYClt5T8ZGetrfKYBcsv/HQjWv6D3Kklwg3RnpoC8mqlW htqYzufKlpb9CwWPIhYtzu3hB5MVsze1A5SKxjdmAjZpLUPgoRHGwP+db7FJWi3X8pvmC 4jFp7QCR4IuQLvhm7IE80/Vsloi6Q2O+6R/QIGAq0uomEyKfG+AreVIYcGdizs3pOoNMn r9JwVp+hGomX/aSGA9ESStb0S31U9lI1is9Bla4fQ5SE4foXkARusJhI2vwoz6zjYTLqF 5exGAp6zucL8ANu9YYwhNt/Fs8XtRQpiIjzGBADOB61tHCi+m2TV9t4WuTLwoEkewVQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793819830; h=Received:DKIM-Signature:Subject:To:Cc:From:Date:Message-ID: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=vnWDbXrs3/3tjfAl7+qPORhCRRgFkvsIQZZ1CCw0W4c=; b=2g31F8EmrV1/elMI3McHmhE+F3Iqu0uFJfgCtseXfjO/0ou3fMzOXYJ26L5/HQhEcY3K g9nF4RZ+mSMsJORvQBzH8DMfxH+WoVLkO/CgoBA/+F62YId+wvz7M2u10Q94kmCVwPaHN B6nDHwEBSm8JxRB8PBrzMtGvUO9aaiIlmaxbA7CbA9kwLd87dzxeHINyklFwdqv9lOXSM MRalF27OF9VtWrb+0jvANIybdalCwiWGQN6Sd4TnPvysDXBOq70Nn01nBVsfXYZrgxoFg XeHDH6qOnyD35oIctdO/vYquMwDOOZJnOFe8+Q7LhHvAn74oZm0d1FoGtnAc9MFZj1Q== 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=fRygZGeS; 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 F3151606D83E for ; Wed, 4 Nov 2026 19:17:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=fRygZGeS Received: by smtp.kernel.org (Postfix) with ESMTPSA id 94EAC1F00A1A; Wed, 4 Nov 2026 19:17:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793819829; bh=vnWDbXrs3/3tjfAl7+qPORhCRRgFkvsIQZZ1CCw0W4c=; h=Subject:To:Cc:From:Date; b=fRygZGeSOWHrJdgLes2BfoPUkkuKlmuatb4/NiCkNfcm9mJWS1H8Mkz0Vr1BYAErZ rSSq7eoXhYkcAI/RAruNoLRh/gf4BA2S4ZVkkYaEIsd9uykG/QUATooTm+cBeWycui wTxlcFdS5+rOceVHBRM0hHU6dBDiza7wjmpaZoOk= Subject: FAILED: patch "[PATCH] KVM: Only bind memslot to guest_memfd instance for CREATE" failed to apply to 5.15-stable tree To: seanjc@google.com,david@kernel.org Cc: From: Date: Wed, 04 Nov 2026 14:17:01 -0500 Message-ID: <2026110400-expend-attain-5e68@gregkh> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 513333a5546017da2a4a6173bfb70372f83733b3 # git commit -s git send-email --to '' --in-reply-to '2026110400-expend-attain-5e68@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 513333a5546017da2a4a6173bfb70372f83733b3 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Mon, 21 Sep 2026 17:13:29 -0700 Subject: [PATCH] KVM: Only bind memslot to guest_memfd instance for CREATE operations 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 diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 3c0dbe60a5b4..c53a88cea1f2 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1742,10 +1742,10 @@ 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); @@ -2106,7 +2106,7 @@ static 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; @@ -2119,7 +2119,7 @@ static 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);