On 02.03.21 17:21, David Hildenbrand wrote:
Similar to VFIO, vDPA will go ahead an map+pin all guest memory. Memory that used to be discarded will get re-populated and if we discard+re-access memory after mapping+pinning, the pages mapped into the vDPA IOMMU will go out of sync with the actual pages mapped into the user space page tables.Set discarding of RAM broken such that: - virtio-mem and vhost-vdpa run mutually exclusive - virtio-balloon is inhibited and no memory discards will get issued In the future, we might be able to support coordinated discarding of RAM as used by virtio-mem and as planned for VFIO. Cc: Jason Wang <jasow...@redhat.com> Cc: Michael S. Tsirkin <m...@redhat.com> Cc: Cindy Lu <l...@redhat.com> Signed-off-by: David Hildenbrand <da...@redhat.com> --- Note: I was not actually able to reproduce/test as I fail to get the vdpa_sim/vdpa_sim_net running on upstream Linux (whetever vdpa, vhost_vdpa, vdpa_sim, vdpa_sim_net modules I probe, and in which order, no vdpa devices appear under /sys/bus/vdpa/devices/ or /dev/). --- hw/virtio/vhost-vdpa.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c index 01d2101d09..86058d4041 100644 --- a/hw/virtio/vhost-vdpa.c +++ b/hw/virtio/vhost-vdpa.c @@ -278,6 +278,17 @@ static int vhost_vdpa_init(struct vhost_dev *dev, void *opaque) uint64_t features; assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_VDPA); trace_vhost_vdpa_init(dev, opaque); + int ret; + + /* + * Similar to VFIO, we end up pinning all guest memory and have to + * disable discarding of RAM. + */ + ret = ram_block_discard_disable(true); + if (ret) { + error_report("Cannot set discarding of RAM broken"); + return ret; + }v = opaque;v->dev = dev; @@ -302,6 +313,8 @@ static int vhost_vdpa_cleanup(struct vhost_dev *dev) memory_listener_unregister(&v->listener);dev->opaque = NULL;+ ram_block_discard_disable(false); + return 0; }
@MST, do you have this on your radar? thanks -- Thanks, David / dhildenb
