From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 851E73C343F for ; Thu, 16 Jul 2026 12:46:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784205980; cv=none; b=NtYTN7/oCRDTiYeY0irG0eH88kVa9zhdcu8wu1cuEZpZnfHcUt0ZyqyxokzGa4wco2vRNjCGvRmjCHlydoIKyl94IoE1m3+NJhWKqLhWQSIKU1l6zjlf+kHazmGIHZcip6UPUfGQN4NIz01vzl0Q6UIPsoXNQFSqj1ht+PGgZ4Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784205980; c=relaxed/simple; bh=TKGwRuS6UabsaqzGJk96kLmJRu8zBiaiZ7bqL8Ogskc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=K0+dfgP2sTEj2onqgjslT/u1xS7qZYBn6uJljT5oatF2B1Blk8U7gxYx4Vshms4XZfTu3n1b901TWcDBwZ94Kdxgd1OX3lXVnUT2CSjPmpVHUJA2wkvihaMiDtJQnsdP0UYvEpcF67Dgw7kOHo3QN8GN1aptAWor6ErkjzIlsRo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=PiA1i4Hu; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="PiA1i4Hu" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1784205978; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ljzVg7xF81fBVO0UzYeEB67bBG4Cr0VEw/T/0BtN7VU=; b=PiA1i4Hu3H6gy0dB4NH39yCSlwKKwZHVnaLqrZSFUFLJF3uzn8J9aZu+x2O2Bhx6j9nt+t /sIAgljtZeQOqN7ezWF1114DoNXcE+3jXaFDbynX8VBCaGFEFl+kphQjYzjf01hgD+mSlF Jrj4radLyVLL7dDkwG1mQ3eT/2SNZPk= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-45-Dap_adHSOCe4LHnVxH_Dfw-1; Thu, 16 Jul 2026 08:46:14 -0400 X-MC-Unique: Dap_adHSOCe4LHnVxH_Dfw-1 X-Mimecast-MFC-AGG-ID: Dap_adHSOCe4LHnVxH_Dfw_1784205973 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 87A211954B30; Thu, 16 Jul 2026 12:46:13 +0000 (UTC) Received: from localhost (unknown [10.2.16.131]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 466D01800370; Thu, 16 Jul 2026 12:46:12 +0000 (UTC) Date: Thu, 16 Jul 2026 10:50:25 +0100 From: Stefan Hajnoczi To: Alexander Graf Cc: virtio-comment@lists.linux.dev, "Michael S. Tsirkin" , Jason Wang Subject: Re: [PATCH] Add VIRTIO_F_DMB (Device Memory Buffer) Message-ID: <20260716095025.GB741667@fedora> References: <20260702040006.65669-1-graf@amazon.com> Precedence: bulk X-Mailing-List: virtio-comment@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="A4x0pOVuHM9U7Afj" Content-Disposition: inline In-Reply-To: <20260702040006.65669-1-graf@amazon.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 --A4x0pOVuHM9U7Afj Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Thu, Jul 02, 2026 at 04:00:06AM +0000, Alexander Graf wrote: > * Shared memory region id: DMB needs a well-known shmid so the driver can > locate the region independent of device type. This draft reserves shmid 2 > and adds a "Reserved Shared Memory Region IDs" registry. However shmid is > currently a per-device-type namespace, and at least one device type > (virtio-scmi) documents the entire shmid space as its own. Guidance > requested on the preferred mechanism: (a) a small transport-reserved shmid > range with device types adjusted to exclude it, or (b) identifying the DMB > region by a means other than a fixed shmid. The exact number is not fixed > pending this decision. Hi Alex, VIRTIO Transports could provide a way to fetch the DMB shmid. For example, the MMIO transport would get a new read-only DMBSHMId register that contains a valid shmid when VIRTIO_F_DMB has been negotiated. Allowing the device to report an arbitrary shmid is flexible - it won't interfere with device-specific Shared Memory Regions or future Transport-specific Shared Memory Regions. 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