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mx.microsoft.com 1; spf=pass\n smtp.mailfrom=nutanix.com; dmarc=pass action=none header.from=nutanix.com;\n dkim=pass header.d=nutanix.com; arc=none","From":"John Levon ","To":"qemu-devel@nongnu.org","Cc":"Thanos Makatos ,\n Pierrick Bouvier , =?utf-8?q?C=C3=A9dric_Le_Go?=\n\t=?utf-8?q?ater?= , John Levon ,\n Patrick Mooney ","Subject":"[PATCH 3/3] vfio-user: fix DMA write reply","Date":"Thu, 9 Apr 2026 11:47:56 +0100","Message-ID":"<20260409104756.465294-4-john.levon@nutanix.com>","X-Mailer":"git-send-email 2.43.0","In-Reply-To":"<20260409104756.465294-1-john.levon@nutanix.com>","References":"<20260409104756.465294-1-john.levon@nutanix.com>","Content-Transfer-Encoding":"8bit","Content-Type":"text/plain","X-ClientProxiedBy":"LO2P123CA0057.GBRP123.PROD.OUTLOOK.COM\n (2603:10a6:600:1::21) To CH2PR02MB6760.namprd02.prod.outlook.com\n (2603:10b6:610:7f::9)","MIME-Version":"1.0","X-MS-PublicTrafficType":"Email","X-MS-TrafficTypeDiagnostic":"CH2PR02MB6760:EE_|SJ0PR02MB7597:EE_","X-MS-Office365-Filtering-Correlation-Id":"c976a49b-6142-4f1e-ed15-08de96257ad0","x-proofpoint-crosstenant":"true","X-MS-Exchange-SenderADCheck":"1","X-MS-Exchange-AntiSpam-Relay":"0","X-Microsoft-Antispam":"BCL:0;\n ARA:13230040|366016|376014|1800799024|22082099003|18002099003|56012099003;","X-Microsoft-Antispam-Message-Info":"\n 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","X-Forefront-Antispam-Report":"CIP:255.255.255.255; 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helo=mx0a-002c1b01.pphosted.com","X-Spam_score_int":"-32","X-Spam_score":"-3.3","X-Spam_bar":"---","X-Spam_report":"(-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.54,\n DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001,\n RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=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":"The 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 \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 d4766487ea..12deb25102 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 64b8b3cb8c..facc79727a 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":["3/3"]}