vfio-user: implement VFIO_USER_DMA_READ/WRITE

Unlike most other messages, this is a server->client message, for when a
server wants to do "DMA"; this is slow, so normally the server has
memory directly mapped instead.

Originally-by: John Johnson <john.g.johnson@oracle.com>
Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
Signed-off-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250625193012.2316242-15-john.levon@nutanix.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

1 files changed, 111 insertions, 0 deletions

diff --git a/hw/vfio-user/pci.c b/hw/vfio-user/pci.c
index 49d12763ab..040660d197 100644
--- a/hw/vfio-user/pci.c
+++ b/hw/vfio-user/pci.c
@@ -9,6 +9,7 @@
 #include <sys/ioctl.h>
 #include "qemu/osdep.h"
 #include "qapi-visit-sockets.h"
+#include "qemu/error-report.h"
 
 #include "hw/qdev-properties.h"
 #include "hw/vfio/pci.h"
@@ -80,6 +81,95 @@ static void vfio_user_msix_teardown(VFIOPCIDevice *vdev)
     vdev->msix->pba_region = NULL;
 }
 
+static void vfio_user_dma_read(VFIOPCIDevice *vdev, VFIOUserDMARW *msg)
+{
+    PCIDevice *pdev = &vdev->pdev;
+    VFIOUserProxy *proxy = vdev->vbasedev.proxy;
+    VFIOUserDMARW *res;
+    MemTxResult r;
+    size_t size;
+
+    if (msg->hdr.size < sizeof(*msg)) {
+        vfio_user_send_error(proxy, &msg->hdr, EINVAL);
+        return;
+    }
+    if (msg->count > proxy->max_xfer_size) {
+        vfio_user_send_error(proxy, &msg->hdr, E2BIG);
+        return;
+    }
+
+    /* switch to our own message buffer */
+    size = msg->count + sizeof(VFIOUserDMARW);
+    res = g_malloc0(size);
+    memcpy(res, msg, sizeof(*res));
+    g_free(msg);
+
+    r = pci_dma_read(pdev, res->offset, &res->data, res->count);
+
+    switch (r) {
+    case MEMTX_OK:
+        if (res->hdr.flags & VFIO_USER_NO_REPLY) {
+            g_free(res);
+            return;
+        }
+        vfio_user_send_reply(proxy, &res->hdr, size);
+        break;
+    case MEMTX_ERROR:
+        vfio_user_send_error(proxy, &res->hdr, EFAULT);
+        break;
+    case MEMTX_DECODE_ERROR:
+        vfio_user_send_error(proxy, &res->hdr, ENODEV);
+        break;
+    case MEMTX_ACCESS_ERROR:
+        vfio_user_send_error(proxy, &res->hdr, EPERM);
+        break;
+    default:
+        error_printf("vfio_user_dma_read unknown error %d\n", r);
+        vfio_user_send_error(vdev->vbasedev.proxy, &res->hdr, EINVAL);
+    }
+}
+
+static void vfio_user_dma_write(VFIOPCIDevice *vdev, VFIOUserDMARW *msg)
+{
+    PCIDevice *pdev = &vdev->pdev;
+    VFIOUserProxy *proxy = vdev->vbasedev.proxy;
+    MemTxResult r;
+
+    if (msg->hdr.size < sizeof(*msg)) {
+        vfio_user_send_error(proxy, &msg->hdr, EINVAL);
+        return;
+    }
+    /* make sure transfer count isn't larger than the message data */
+    if (msg->count > msg->hdr.size - sizeof(*msg)) {
+        vfio_user_send_error(proxy, &msg->hdr, E2BIG);
+        return;
+    }
+
+    r = pci_dma_write(pdev, msg->offset, &msg->data, msg->count);
+
+    switch (r) {
+    case MEMTX_OK:
+        if ((msg->hdr.flags & VFIO_USER_NO_REPLY) == 0) {
+            vfio_user_send_reply(proxy, &msg->hdr, sizeof(msg->hdr));
+        } else {
+            g_free(msg);
+        }
+        break;
+    case MEMTX_ERROR:
+        vfio_user_send_error(proxy, &msg->hdr, EFAULT);
+        break;
+    case MEMTX_DECODE_ERROR:
+        vfio_user_send_error(proxy, &msg->hdr, ENODEV);
+        break;
+    case MEMTX_ACCESS_ERROR:
+        vfio_user_send_error(proxy, &msg->hdr, EPERM);
+        break;
+    default:
+        error_printf("vfio_user_dma_write unknown error %d\n", r);
+        vfio_user_send_error(vdev->vbasedev.proxy, &msg->hdr, EINVAL);
+    }
+}
+
 /*
  * Incoming request message callback.
  *
@@ -87,7 +177,28 @@ static void vfio_user_msix_teardown(VFIOPCIDevice *vdev)
  */
 static void vfio_user_pci_process_req(void *opaque, VFIOUserMsg *msg)
 {
+    VFIOPCIDevice *vdev = opaque;
+    VFIOUserHdr *hdr = msg->hdr;
+
+    /* no incoming PCI requests pass FDs */
+    if (msg->fds != NULL) {
+        vfio_user_send_error(vdev->vbasedev.proxy, hdr, EINVAL);
+        vfio_user_putfds(msg);
+        return;
+    }
 
+    switch (hdr->command) {
+    case VFIO_USER_DMA_READ:
+        vfio_user_dma_read(vdev, (VFIOUserDMARW *)hdr);
+        break;
+    case VFIO_USER_DMA_WRITE:
+        vfio_user_dma_write(vdev, (VFIOUserDMARW *)hdr);
+        break;
+    default:
+        error_printf("vfio_user_pci_process_req unknown cmd %d\n",
+                     hdr->command);
+        vfio_user_send_error(vdev->vbasedev.proxy, hdr, ENOSYS);
+    }
 }
 
 /*