Re: [PATCH v5 7/7] vhost-user-devive: Add shmem BAR

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Mon, Jun 09, 2025 at 04:47:29PM +0200, Albert Esteve wrote:
> diff --git a/hw/virtio/vhost-user-device-pci.c b/hw/virtio/vhost-user-device-pci.c
> index f10bac874e..eeb52671a0 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 2

This BAR number conflicts with `--device
vhost-user-device-pci,modern-pio-notify=on`. Please take a look at the
how other devices using VIRTIO Shared Memory arrange BARs.

> +
>  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);
> +    VirtSharedMemory *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) {
> +        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, 0);

The last argument is the shmid. It cannot be hardcoded to 0.

> +            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);
> +    }
>  }
>  
>  static void vhost_user_device_pci_class_init(ObjectClass *klass,
> -- 
> 2.49.0
> 

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