On Tue, Oct 14, 2025 at 5:18 PM Stefan Hajnoczi <[email protected]> wrote: > > On Mon, Oct 13, 2025 at 05:37:52PM +0200, Albert Esteve wrote: > > On Mon, Sep 29, 2025 at 9:00 PM Stefan Hajnoczi <[email protected]> wrote: > > > > > > On Wed, Sep 10, 2025 at 01:54:20PM +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 <[email protected]> > > > > --- > > > > hw/virtio/vhost-user-base.c | 47 +++++++++++++++++++++++++++++-- > > > > hw/virtio/vhost-user-device-pci.c | 34 ++++++++++++++++++++-- > > > > 2 files changed, 76 insertions(+), 5 deletions(-) > > > > > > > > diff --git a/hw/virtio/vhost-user-base.c b/hw/virtio/vhost-user-base.c > > > > index ff67a020b4..82f49500e4 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, regions_processed = 0; > > > > > > > > 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 +336,49 @@ 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 < VIRTIO_MAX_SHMEM_REGIONS && regions_processed < > > > > nregions; i++) { > > > > + if (memory_sizes[i]) { > > > > + regions_processed++; > > > > + 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; > > > > + } > > > > + > > > > + virtio_new_shmem_region(vdev, i, memory_sizes[i]); > > > > + } > > > > } > > > > > > > > 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 > > > > > > 64-bit PCI memory BARs require two contiguous 32-bit BARs. Choosing BAR > > > 3 won't work because modern_mem_bar_idx = 4 (and 5) and there is a > > > collision. > > > > > > virtio-gpu-hostmem uses BAR 2 and 3 for VIRTIO Shared Memory Regions. In > > > order to do this, it rearranges the other VIRTIO PCI BARs in > > > virtio_vga_base_realize(). Following that approach should be safe. > > > > I see. But doing the same strategy would collide with > > virtio-gpu-hostmem if both devices are used simultaneously? Would that > > be ok? > > virtio-gpu-* and vhost-user-device-pci are separate PCI devices with > their own BARs, how would they conflict?
Ah! I see. I thought different devices registering the same IDs would conflict. But you're right, it doesn't make sense. Understood. Then I'll follow your initial suggestion.
