On Mon, Aug 18, 2025 at 12:03:53PM +0200, Albert Esteve wrote:
> Add shared memory BAR support to vhost-user-device-pci
> to enable direct file mapping for VIRTIO Shared
> Memory Regions.
>
> The implementation creates a consolidated shared
> memory BAR that contains all VIRTIO Shared
> Memory Regions as subregions. Each region is
> configured with its proper shmid, size, and
> offset within the BAR. The number and size of
> regions are retrieved via VHOST_USER_GET_SHMEM_CONFIG
> message sent by vhost-user-base during realization
> after virtio_init().
>
> Specifiically, it uses BAR 3 to avoid conflicts, as
> it is currently unused.
>
> The shared memory BAR is only created when the
> backend supports VHOST_USER_PROTOCOL_F_SHMEM and
> has configured shared memory regions. This maintains
> backward compatibility with backends that do not
> support shared memory functionality.
>
> Signed-off-by: Albert Esteve <aest...@redhat.com>
> ---
> hw/virtio/vhost-user-base.c | 49 +++++++++++++++++++++++++++++--
> hw/virtio/vhost-user-device-pci.c | 34 +++++++++++++++++++--
> 2 files changed, 78 insertions(+), 5 deletions(-)
>
> diff --git a/hw/virtio/vhost-user-base.c b/hw/virtio/vhost-user-base.c
> index ff67a020b4..932f9b5596 100644
> --- a/hw/virtio/vhost-user-base.c
> +++ b/hw/virtio/vhost-user-base.c
> @@ -16,6 +16,7 @@
> #include "hw/virtio/virtio-bus.h"
> #include "hw/virtio/vhost-user-base.h"
> #include "qemu/error-report.h"
> +#include "migration/blocker.h"
>
> static void vub_start(VirtIODevice *vdev)
> {
> @@ -276,7 +277,9 @@ static void vub_device_realize(DeviceState *dev, Error
> **errp)
> {
> VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> VHostUserBase *vub = VHOST_USER_BASE(dev);
> - int ret;
> + uint64_t memory_sizes[VIRTIO_MAX_SHMEM_REGIONS];
> + g_autofree char *name = NULL;
> + int i, ret, nregions;
>
> if (!vub->chardev.chr) {
> error_setg(errp, "vhost-user-base: missing chardev");
> @@ -319,7 +322,7 @@ static void vub_device_realize(DeviceState *dev, Error
> **errp)
>
> /* Allocate queues */
> vub->vqs = g_ptr_array_sized_new(vub->num_vqs);
> - for (int i = 0; i < vub->num_vqs; i++) {
> + for (i = 0; i < vub->num_vqs; i++) {
> g_ptr_array_add(vub->vqs,
> virtio_add_queue(vdev, vub->vq_size,
> vub_handle_output));
> @@ -333,11 +336,51 @@ static void vub_device_realize(DeviceState *dev, Error
> **errp)
> VHOST_BACKEND_TYPE_USER, 0, errp);
>
> if (ret < 0) {
> - do_vhost_user_cleanup(vdev, vub);
> + goto err;
> + }
> +
> + ret = vub->vhost_dev.vhost_ops->vhost_get_shmem_config(&vub->vhost_dev,
> + &nregions,
> + memory_sizes,
> + errp);
> +
> + if (ret < 0) {
> + goto err;
> + }
> +
> + for (i = 0; i < nregions; i++) {
> + if (memory_sizes[i]) {
> + if (vub->vhost_dev.migration_blocker == NULL) {
> + error_setg(&vub->vhost_dev.migration_blocker,
> + "Migration disabled: devices with VIRTIO Shared
> Memory "
> + "Regions do not support migration yet.");
> + ret = migrate_add_blocker_normal(
> + &vub->vhost_dev.migration_blocker,
> + errp);
> +
> + if (ret < 0) {
> + goto err;
> + }
> + }
> +
> + if (memory_sizes[i] % qemu_real_host_page_size() != 0) {
> + error_setg(errp, "Shared memory %d size must be a power of 2
> "
> + "no smaller than the page size", i);
> + goto err;
> + }
> +
> + name = g_strdup_printf("vub-shm-%d", i);
name is leaked because it's scope extends until the end of the function
(after the loop) but a newly allocated string is assigned each time
around the loop. This can be fixed by moving the local variable
declaration inside the if statement body.
> + memory_region_init(&virtio_new_shmem_region(vdev, i)->mr,
> + OBJECT(vdev), name,
> + memory_sizes[i]);
->mr is already initialized inside virtio_new_shmem_region(). I suggest
changing the definition of virtio_new_shmem_region() like this:
void virtio_add_shmem_region(VirtIODevice *vdev, uint8_t shmid,
uint64_t size)
and then calling it like this:
virtio_add_shmem_region(vdev, shmid, memory_sizes[i]);
("new" usually returns a new instance whereas "add" modifies an owner
object/container. I think "add" is more appropriate here.)
> + }
> }
>
> qemu_chr_fe_set_handlers(&vub->chardev, NULL, NULL, vub_event, NULL,
> dev, NULL, true);
> + return;
> +err:
> + do_vhost_user_cleanup(vdev, vub);
> }
>
> static void vub_device_unrealize(DeviceState *dev)
> diff --git a/hw/virtio/vhost-user-device-pci.c
> b/hw/virtio/vhost-user-device-pci.c
> index f10bac874e..bac99e7c60 100644
> --- a/hw/virtio/vhost-user-device-pci.c
> +++ b/hw/virtio/vhost-user-device-pci.c
> @@ -8,14 +8,18 @@
> */
>
> #include "qemu/osdep.h"
> +#include "qapi/error.h"
> #include "hw/qdev-properties.h"
> #include "hw/virtio/vhost-user-base.h"
> #include "hw/virtio/virtio-pci.h"
>
> +#define VIRTIO_DEVICE_PCI_SHMEM_BAR 3
> +
> struct VHostUserDevicePCI {
> VirtIOPCIProxy parent_obj;
>
> VHostUserBase vub;
> + MemoryRegion shmembar;
> };
>
> #define TYPE_VHOST_USER_DEVICE_PCI "vhost-user-device-pci-base"
> @@ -25,10 +29,36 @@ OBJECT_DECLARE_SIMPLE_TYPE(VHostUserDevicePCI,
> VHOST_USER_DEVICE_PCI)
> static void vhost_user_device_pci_realize(VirtIOPCIProxy *vpci_dev, Error
> **errp)
> {
> VHostUserDevicePCI *dev = VHOST_USER_DEVICE_PCI(vpci_dev);
> - DeviceState *vdev = DEVICE(&dev->vub);
> + DeviceState *dev_state = DEVICE(&dev->vub);
> + VirtIODevice *vdev = VIRTIO_DEVICE(dev_state);
> + VirtioSharedMemory *shmem, *next;
> + uint64_t offset = 0, shmem_size = 0;
>
> vpci_dev->nvectors = 1;
> - qdev_realize(vdev, BUS(&vpci_dev->bus), errp);
> + qdev_realize(dev_state, BUS(&vpci_dev->bus), errp);
> +
> + QSIMPLEQ_FOREACH_SAFE(shmem, &vdev->shmem_list, entry, next) {
This is not specific to vhost-user-device-pci.c. All VIRTIO devices with
Shared Memory Regions need PCI BAR setup code. Since vdev->shmem_list is
part of the core hw/virtio/ code, it would make sense to move this into
into hw/virtio/virtio-pci.c.
> + if (shmem->mr.size > UINT64_MAX - shmem_size) {
> + error_setg(errp, "Total shared memory required overflow");
> + return;
> + }
> + shmem_size = shmem_size + shmem->mr.size;
> + }
> + if (shmem_size) {
> + memory_region_init(&dev->shmembar, OBJECT(vpci_dev),
> + "vhost-device-pci-shmembar", shmem_size);
> + QSIMPLEQ_FOREACH_SAFE(shmem, &vdev->shmem_list, entry, next) {
> + memory_region_add_subregion(&dev->shmembar, offset, &shmem->mr);
> + virtio_pci_add_shm_cap(vpci_dev, VIRTIO_DEVICE_PCI_SHMEM_BAR,
> + offset, shmem->mr.size, shmem->shmid);
> + offset = offset + shmem->mr.size;
> + }
> + pci_register_bar(&vpci_dev->pci_dev, VIRTIO_DEVICE_PCI_SHMEM_BAR,
> + PCI_BASE_ADDRESS_SPACE_MEMORY |
> + PCI_BASE_ADDRESS_MEM_PREFETCH |
> + PCI_BASE_ADDRESS_MEM_TYPE_64,
> + &dev->shmembar);
This does not follow the same approach as virtio-gpu-pci.c and
virtio-vga.c. They config the VirtIOPCIProxy's BARs
(->modern_io_bar_idx, ->modern_mem_bar_idx, and ->msix_bar_idx) to
control the BAR layout first and then call qdev_realize().
Why does this patch do things differently? It looks like it's assuming
vpci_dev always has a specific BAR layout (it could change).
> + }
> }
>
> static void vhost_user_device_pci_class_init(ObjectClass *klass,
> --
> 2.49.0
>
signature.asc
Description: PGP signature
