{"id":2225847,"url":"http://patchwork.ozlabs.org/api/patches/2225847/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260421163438.3447280-15-clg@redhat.com/","project":{"id":14,"url":"http://patchwork.ozlabs.org/api/projects/14/?format=json","name":"QEMU Development","link_name":"qemu-devel","list_id":"qemu-devel.nongnu.org","list_email":"qemu-devel@nongnu.org","web_url":"","scm_url":"","webscm_url":"","list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"<20260421163438.3447280-15-clg@redhat.com>","list_archive_url":null,"date":"2026-04-21T16:34:38","name":"[PULL,14/14] vfio-user: fix DMA write reply","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"e1bde85269edd32d2abc70a61bdf9aa9942e5059","submitter":{"id":85406,"url":"http://patchwork.ozlabs.org/api/people/85406/?format=json","name":"Cédric Le Goater","email":"clg@redhat.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260421163438.3447280-15-clg@redhat.com/mbox/","series":[{"id":500853,"url":"http://patchwork.ozlabs.org/api/series/500853/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/list/?series=500853","date":"2026-04-21T16:34:24","name":"[PULL,01/14] hw/vfio/listener.c: remove CONFIG_KVM","version":1,"mbox":"http://patchwork.ozlabs.org/series/500853/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2225847/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2225847/checks/","tags":{},"related":[],"headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=fncuQVJR;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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Tue, 21 Apr 2026 12:35:41 -0400","from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com\n (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by\n relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3,\n cipher=TLS_AES_256_GCM_SHA384) id us-mta-308-kl6Dm1SGPSGekxQN19MjgQ-1; Tue,\n 21 Apr 2026 12:35:14 -0400","from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com\n (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17])\n (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest\n SHA256)\n (No client certificate requested)\n by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS\n id 817DA19560AD; Tue, 21 Apr 2026 16:35:13 +0000 (UTC)","from corto.redhat.com (unknown [10.44.32.70])\n by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP\n id BBAB71956095; Tue, 21 Apr 2026 16:35:11 +0000 (UTC)"],"DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;\n s=mimecast20190719; t=1776789317;\n h=from:from:reply-to:subject:subject:date:date:message-id:message-id:\n to:to:cc:cc:mime-version:mime-version:content-type:content-type:\n content-transfer-encoding:content-transfer-encoding:\n in-reply-to:in-reply-to:references:references;\n bh=L4boacDBWXxI5RCVqYYkYH11QOnnmQygqQshHe9V5xU=;\n b=fncuQVJRDaTBWjn7CDKq7vGkRQXiPqfCCvw+zgJkyv7OKtUY+fQskfv8XwvpWdUZmYfyYL\n wdLUed9mrWOd78oLyLQtCj+XOQj4Fgvq8G2o2HoBARzY5ug75w8bapMBCXSl6HrbXoncTF\n t+qV91WQcSDBRfIXcrnlbZ2BbTxYum0=","X-MC-Unique":"kl6Dm1SGPSGekxQN19MjgQ-1","X-Mimecast-MFC-AGG-ID":"kl6Dm1SGPSGekxQN19MjgQ_1776789313","From":"=?utf-8?q?C=C3=A9dric_Le_Goater?= ","To":"qemu-devel@nongnu.org","Cc":"Alex Williamson , John Levon ,\n Patrick Mooney ,\n =?utf-8?q?C=C3=A9dric_Le_Goater?= ","Subject":"[PULL 14/14] vfio-user: fix DMA write reply","Date":"Tue, 21 Apr 2026 18:34:38 +0200","Message-ID":"<20260421163438.3447280-15-clg@redhat.com>","In-Reply-To":"<20260421163438.3447280-1-clg@redhat.com>","References":"<20260421163438.3447280-1-clg@redhat.com>","MIME-Version":"1.0","Content-Type":"text/plain; charset=UTF-8","Content-Transfer-Encoding":"8bit","X-Scanned-By":"MIMEDefang 3.0 on 10.30.177.17","Received-SPF":"pass client-ip=170.10.133.124; envelope-from=clg@redhat.com;\n helo=us-smtp-delivery-124.mimecast.com","X-Spam_score_int":"-20","X-Spam_score":"-2.1","X-Spam_bar":"--","X-Spam_report":"(-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001,\n DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_PASS=-0.001,\n SPF_PASS=-0.001 autolearn=ham autolearn_force=no","X-Spam_action":"no action","X-BeenThere":"qemu-devel@nongnu.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"qemu development ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org","Sender":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org"},"content":"From: John Levon \n\nThe protocol specifies that DMA write replies should include\naddress+count, but the client code was only doing so for read. Fix that\nup.\n\nIn addition, add a protocol clarification over how short writes may be\nreported in that reply. QEMU never reports a short write via the\ncount field.\n\nReported-by: Patrick Mooney \nSigned-off-by: John Levon \nReviewed-by: Cédric Le Goater \nLink: https://lore.kernel.org/qemu-devel/20260410085716.877185-4-john.levon@nutanix.com\nSigned-off-by: Cédric Le Goater \n---\n docs/interop/vfio-user.rst | 6 ++++++\n hw/vfio-user/pci.c | 30 ++++++++++++++++++++++--------\n 2 files changed, 28 insertions(+), 8 deletions(-)","diff":"diff --git a/docs/interop/vfio-user.rst b/docs/interop/vfio-user.rst\nindex d4766487ea6d0ee021316890d443814957cf6284..12deb25102af217f7f292b4cb655dc4a6a92439a 100644\n--- a/docs/interop/vfio-user.rst\n+++ b/docs/interop/vfio-user.rst\n@@ -1429,6 +1429,9 @@ Reply\n * *count* is the size of the data transferred.\n * *data* is the data read.\n \n+Note that whether short reads return an error or just set count appropriately is\n+a client-side choice; servers should be prepared to handle both cases.\n+\n ``VFIO_USER_DMA_WRITE``\n -----------------------\n \n@@ -1469,6 +1472,9 @@ Reply\n * *address* is the client DMA memory address being accessed.\n * *count* is the size of the data transferred.\n \n+Note that whether short writes return an error or just set count appropriately\n+is a client-side choice; servers should be prepared to handle both cases.\n+\n ``VFIO_USER_DEVICE_RESET``\n --------------------------\n \ndiff --git a/hw/vfio-user/pci.c b/hw/vfio-user/pci.c\nindex 64b8b3cb8cf5d66879af1703c4f2b5ae0c7418ca..facc79727acb82c35fec5b4bef79e78b3878531a 100644\n--- a/hw/vfio-user/pci.c\n+++ b/hw/vfio-user/pci.c\n@@ -109,6 +109,10 @@ static void vfio_user_dma_read(VFIOPCIDevice *vdev, VFIOUserDMARW *msg)\n \n r = pci_dma_read(pdev, res->offset, &res->data, res->count);\n \n+ /*\n+ * pci_dma_read() doesn't support reporting short reads via the reply's\n+ * count parameter; in this case, we'll reply with an error instead.\n+ */\n switch (r) {\n case MEMTX_OK:\n if (res->hdr.flags & VFIO_USER_NO_REPLY) {\n@@ -136,6 +140,7 @@ static void vfio_user_dma_write(VFIOPCIDevice *vdev, VFIOUserDMARW *msg)\n {\n PCIDevice *pdev = PCI_DEVICE(vdev);\n VFIOUserProxy *proxy = vdev->vbasedev.proxy;\n+ VFIOUserDMARW *res;\n MemTxResult r;\n \n if (msg->hdr.size < sizeof(*msg)) {\n@@ -150,26 +155,35 @@ static void vfio_user_dma_write(VFIOPCIDevice *vdev, VFIOUserDMARW *msg)\n \n r = pci_dma_write(pdev, msg->offset, &msg->data, msg->count);\n \n+ res = g_malloc0(sizeof(*res));\n+ memcpy(res, msg, sizeof(*res));\n+ g_free(msg);\n+\n+ /*\n+ * pci_dma_write() doesn't support reporting short writes via the reply's\n+ * count parameter; in this case, we'll reply with an error instead.\n+ */\n switch (r) {\n case MEMTX_OK:\n- if ((msg->hdr.flags & VFIO_USER_NO_REPLY) == 0) {\n- vfio_user_send_reply(proxy, &msg->hdr, sizeof(msg->hdr));\n- } else {\n- g_free(msg);\n+ if (res->hdr.flags & VFIO_USER_NO_REPLY) {\n+ g_free(res);\n+ return;\n }\n+\n+ vfio_user_send_reply(proxy, &res->hdr, sizeof(*res));\n break;\n case MEMTX_ERROR:\n- vfio_user_send_error(proxy, &msg->hdr, EFAULT);\n+ vfio_user_send_error(proxy, &res->hdr, EFAULT);\n break;\n case MEMTX_DECODE_ERROR:\n- vfio_user_send_error(proxy, &msg->hdr, ENODEV);\n+ vfio_user_send_error(proxy, &res->hdr, ENODEV);\n break;\n case MEMTX_ACCESS_ERROR:\n- vfio_user_send_error(proxy, &msg->hdr, EPERM);\n+ vfio_user_send_error(proxy, &res->hdr, EPERM);\n break;\n default:\n error_printf(\"vfio_user_dma_write unknown error %d\\n\", r);\n- vfio_user_send_error(vdev->vbasedev.proxy, &msg->hdr, EINVAL);\n+ vfio_user_send_error(vdev->vbasedev.proxy, &res->hdr, EINVAL);\n }\n }\n \n","prefixes":["PULL","14/14"]}