From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) (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 E90E62BEC4E for ; Tue, 22 Sep 2026 00:13:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790036020; cv=none; b=TWlnjs55kaFhYsDHwndbDoncWVhiya8jAxG4Psbr0hYPBp6nB/bY10bViMIsxBDetufZ7uZojmDIGRIiE8DyfNSJgVFsA8o+rrL//UtYorrRvAPPUOYohfoVX8IOrzpRi2CdnE/omKWh1f7mMUefHxH5/2jQHWjDNs4zZ2T4Yu8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790036020; c=relaxed/simple; bh=/uWjI8Uu4H+jwIc5bzgv2pY2GKSfTMxj6nuLZ1zl2PU=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=I0Uxc41SX9Gt/A771RDKxQ3MlEnsoWld5JojF8IsoZDbPljsvzBkmLJAyJRk9BJtfzRMFWP53sCKJ4qfUXS8TPykyUooMY7Zl+4sKm81X/4CgYKjYdmnC5ybPz4udu1/rEhjGy0+wzXCJe9/QdWNZOnOo/ggDlFFw/Q9jfLJxCQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=SWMkc23e; arc=none smtp.client-ip=209.85.215.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="SWMkc23e" Received: by mail-pg1-f199.google.com with SMTP id 41be03b00d2f7-cc1b6f65dacso3088680a12.1 for ; Mon, 21 Sep 2026 17:13:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1790036018; x=1790640818; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:reply-to:from:to:cc:subject:date:message-id :reply-to:content-type; bh=turXne4uYV7wcVpOhFPdmOUyNfChurx8+MQeLApE3QQ=; b=SWMkc23eyqHUmYNn9xDXzBgGXhBVq3fwWxL3rbDt4pXFCPz+JhhBMdbxBd06misfcu W4Bg+QaqaZIqHQZeiEYe/39stwqxfV6CopyWWKtCZ41uFn3FS70eN4hdk6KVVbYPI1Wd MnzntsxBTAlmwwkI9p8SjKgWr0WJASEJL6a+4hkZekuN2gRFADoKv9Sz5ZwWWr/z4V+U PPWQUpd8BA7sHq9fs/BC1+gi4RdNbIPgFII6yHR2Fhy4XiZ5Ffzo3u8w5W3G8I4dyATd SbWePZsFf8Wzxda6JfBfck1OaVOFlmKvjp+ljHp97QQG/Q50NHrXa/IcAp8qlfk9qr4X g4pA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1790036018; x=1790640818; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:reply-to:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to:content-type; bh=turXne4uYV7wcVpOhFPdmOUyNfChurx8+MQeLApE3QQ=; b=QC9XuUDEw3F5Cohu0galBqTLcHrH0e1GzXPj6stSWztXlWKQIRDecl0MTkB8v4nBim 1Wq32bu1tYQ+ZK9Mam94MtgyIyRXDLWUk7KgifBoKCODXyblMkdyw7tg7zzNz2ZVf1Tk 9F7TPSxzeRUITAzkRR5p7Bdp1KfXXQx4JNC0hm+0Vf3fiZOMJPSv/e6CMkXBmxoQUTnS 5wHgvTEEp6SKemmDSF3fOGP+bwBN2DHkRTAPbWLwIzyTQg2MXeDOv2/Umlp4wH93OSrC KXxC19q8xMiAb/iEpopu00iSyskzeBeAVU0wFMZx/UQBF5IUINrRmKB+Sn8ko1P1wJpw eFqg== X-Forwarded-Encrypted: i=1; AKwUvBwVaIYT+rDNabIijwsKkLV4jYfZyMbDfz4NeyBUsPK4uSswu1eKyHf//Yqqt+iyr/uAsFY=@vger.kernel.org X-Gm-Message-State: AFuF++lYh7Xl3h0yJJyOsobCVuxpVNftriPv5CLpQE9VxNHHsoD4CIpC 62O8UfG+EqAF+kPPcycxYC+sExAK2/V+uKxW9UfMSaYYtZjWo/XFfZOECwSE+kMeK0F3CA/cYBa nXq2aYw== X-Received: from pgvn10.prod.google.com ([2002:a65:63ca:0:b0:cc4:5907:21e9]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:a10f:b0:3dd:85a9:55a0 with SMTP id adf61e73a8af0-3dd8c5ac31emr18020098637.34.1790036018118; Mon, 21 Sep 2026 17:13:38 -0700 (PDT) Reply-To: Sean Christopherson Date: Mon, 21 Sep 2026 17:13:29 -0700 In-Reply-To: <20260922001332.1121266-1-seanjc@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260922001332.1121266-1-seanjc@google.com> X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog Message-ID: <20260922001332.1121266-4-seanjc@google.com> Subject: [PATCH v5 3/6] KVM: Only bind memslot to guest_memfd instance for CREATE operations From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: David Hildenbrand , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Stefan Teodorescu , Dennis Tighe , Sashiko Bot , Ackerley Tng , Yan Zhao Content-Type: text/plain; charset="UTF-8" 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 when 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 Signed-off-by: Sean Christopherson --- 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 24cf96840827..ccfd5f5102a5 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1752,10 +1752,10 @@ 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); @@ -2116,7 +2116,7 @@ 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; @@ -2129,7 +2129,7 @@ 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); -- 2.55.0.1082.g2b9226bbc0-goog