> -----Original Message----- > From: Bie, Tiwei > Sent: Thursday, April 19, 2018 7:15 PM > To: Michael S. Tsirkin <m...@redhat.com> > Cc: jasow...@redhat.com; alex.william...@redhat.com; pbonz...@redhat.com; > stefa...@redhat.com; qemu-devel@nongnu.org; virtio-dev@lists.oasis- > open.org; Liang, Cunming <cunming.li...@intel.com>; Daly, Dan > <dan.d...@intel.com>; Tan, Jianfeng <jianfeng....@intel.com>; Wang, Zhihong > <zhihong.w...@intel.com>; Wang, Xiao W <xiao.w.w...@intel.com> > Subject: Re: [PATCH v3 6/6] vhost-user: support registering external host > notifiers > > On Wed, Apr 18, 2018 at 07:34:06PM +0300, Michael S. Tsirkin wrote: > > On Thu, Apr 12, 2018 at 11:12:32PM +0800, Tiwei Bie wrote: > > > This patch introduces VHOST_USER_PROTOCOL_F_HOST_NOTIFIER. > > > With this feature negotiated, vhost-user backend can register memory > > > region based host notifiers. And it will allow the guest driver in > > > the VM to notify the hardware accelerator at the vhost-user backend > > > directly. > > > > > > Signed-off-by: Tiwei Bie <tiwei....@intel.com> > > > > Overall I think we can merge this approach, but I have two main > > concerns about this: > > > > 1. Testing. Most people do not have the virtio hardware > > so how to make sure this does not bit rot? > > > > I have an idea: add an option like this to libvhost-user. > > Naturally libvhost-user can not get notified about a write > > to an mmapped area, but it can write a special value there > > (e.g. all-ones?) and then poll it to detect VQ # writes. > > > > Then include a vhost user bridge test with an option like this. > > > > I'd like to see a patch doing this. > > Sure, I'll do it. Thanks for the suggestion! > > > > > 2. Memory barriers. Right now after updating the avail idx, > > virtio does smp_wmb() and then the MMIO write. > > Normal hardware drivers do wmb() which is an sfence. > > Can a PCI device read bypass index write and see a stale > > index value? A compiler barrier is enough on strongly-ordered memory platform. As it doesn't re-order store, PCI device won't see a stale index value. But a weakly-ordered memory needs sfence.
> > It depends on arch's memory model. Cunming will provide more details about > this later. > > > To make virtio pci do wmb() we would need a new feature bit. > > Alternatively I guess we could maybe look at subsystem vendor/device id. > > > > I'd like to see a patch doing one of these things. > > We prefer to add a new feature bit as it's a more robust way to do this. I'll > send > out some patches soon. > > Thank you very much! :) > > Best regards, > Tiwei Bie > > > > > Thanks! > > > > > --- > > > docs/interop/vhost-user.txt | 33 +++++++++++ > > > hw/virtio/vhost-user.c | 123 > +++++++++++++++++++++++++++++++++++++++++ > > > include/hw/virtio/vhost-user.h | 8 +++ > > > 3 files changed, 164 insertions(+) > > > > > > diff --git a/docs/interop/vhost-user.txt > > > b/docs/interop/vhost-user.txt index 534caab18a..9e57b36b20 100644 > > > --- a/docs/interop/vhost-user.txt > > > +++ b/docs/interop/vhost-user.txt > > > @@ -132,6 +132,16 @@ Depending on the request type, payload can be: > > > Payload: Size bytes array holding the contents of the virtio > > > device's configuration space > > > > > > + * Vring area description > > > + ----------------------- > > > + | u64 | size | offset | > > > + ----------------------- > > > + > > > + u64: a 64-bit integer contains vring index and flags > > > + Size: a 64-bit size of this area > > > + Offset: a 64-bit offset of this area from the start of the > > > + supplied file descriptor > > > + > > > In QEMU the vhost-user message is implemented with the following struct: > > > > > > typedef struct VhostUserMsg { > > > @@ -146,6 +156,7 @@ typedef struct VhostUserMsg { > > > VhostUserLog log; > > > struct vhost_iotlb_msg iotlb; > > > VhostUserConfig config; > > > + VhostUserVringArea area; > > > }; > > > } QEMU_PACKED VhostUserMsg; > > > > > > @@ -380,6 +391,7 @@ Protocol features #define > > > VHOST_USER_PROTOCOL_F_CRYPTO_SESSION 7 > > > #define VHOST_USER_PROTOCOL_F_PAGEFAULT 8 > > > #define VHOST_USER_PROTOCOL_F_CONFIG 9 > > > +#define VHOST_USER_PROTOCOL_F_HOST_NOTIFIER 10 > > > > > > Master message types > > > -------------------- > > > @@ -777,6 +789,27 @@ Slave message types > > > the VHOST_USER_NEED_REPLY flag, master must respond with zero when > > > operation is successfully completed, or non-zero otherwise. > > > > > > + * VHOST_USER_SLAVE_VRING_HOST_NOTIFIER_MSG > > > + > > > + Id: 3 > > > + Equivalent ioctl: N/A > > > + Slave payload: vring area description > > > + Master payload: N/A > > > + > > > + Sets host notifier for a specified queue. The queue index is > > > contained > > > + in the u64 field of the vring area description. The host notifier > > > is > > > + described by the file descriptor (typically it's a VFIO device fd) > > > which > > > + is passed as ancillary data and the size (which is mmap size and > > > should > > > + be the same as host page size) and offset (which is mmap offset) > > > carried > > > + in the vring area description. QEMU can mmap the file descriptor > > > based > > > + on the size and offset to get a memory range. Registering a host > > > notifier > > > + means mapping this memory range to the VM as the specified queue's > notify > > > + MMIO region. Slave sends this request to tell QEMU to de-register > > > the > > > + existing notifier if any and register the new notifier if the > > > request is > > > + sent with a file descriptor. > > > + This request should be sent only when > VHOST_USER_PROTOCOL_F_HOST_NOTIFIER > > > + protocol feature has been successfully negotiated. > > > + > > > VHOST_USER_PROTOCOL_F_REPLY_ACK: > > > ------------------------------- > > > The original vhost-user specification only demands replies for > > > certain diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c > > > index 791e0a4763..1cd9c7276b 100644 > > > --- a/hw/virtio/vhost-user.c > > > +++ b/hw/virtio/vhost-user.c > > > @@ -13,6 +13,7 @@ > > > #include "hw/virtio/vhost.h" > > > #include "hw/virtio/vhost-user.h" > > > #include "hw/virtio/vhost-backend.h" > > > +#include "hw/virtio/virtio.h" > > > #include "hw/virtio/virtio-net.h" > > > #include "chardev/char-fe.h" > > > #include "sysemu/kvm.h" > > > @@ -48,6 +49,7 @@ enum VhostUserProtocolFeature { > > > VHOST_USER_PROTOCOL_F_CRYPTO_SESSION = 7, > > > VHOST_USER_PROTOCOL_F_PAGEFAULT = 8, > > > VHOST_USER_PROTOCOL_F_CONFIG = 9, > > > + VHOST_USER_PROTOCOL_F_HOST_NOTIFIER = 10, > > > VHOST_USER_PROTOCOL_F_MAX > > > }; > > > > > > @@ -92,6 +94,7 @@ typedef enum VhostUserSlaveRequest { > > > VHOST_USER_SLAVE_NONE = 0, > > > VHOST_USER_SLAVE_IOTLB_MSG = 1, > > > VHOST_USER_SLAVE_CONFIG_CHANGE_MSG = 2, > > > + VHOST_USER_SLAVE_VRING_HOST_NOTIFIER_MSG = 3, > > > VHOST_USER_SLAVE_MAX > > > } VhostUserSlaveRequest; > > > > > > @@ -136,6 +139,12 @@ static VhostUserConfig c __attribute__ ((unused)); > > > + sizeof(c.size) \ > > > + sizeof(c.flags)) > > > > > > +typedef struct VhostUserVringArea { > > > + uint64_t u64; > > > + uint64_t size; > > > + uint64_t offset; > > > +} VhostUserVringArea; > > > + > > > typedef struct { > > > VhostUserRequest request; > > > > > > @@ -157,6 +166,7 @@ typedef union { > > > struct vhost_iotlb_msg iotlb; > > > VhostUserConfig config; > > > VhostUserCryptoSession session; > > > + VhostUserVringArea area; > > > } VhostUserPayload; > > > > > > typedef struct VhostUserMsg { > > > @@ -638,9 +648,37 @@ static int vhost_user_set_vring_num(struct > vhost_dev *dev, > > > return vhost_set_vring(dev, VHOST_USER_SET_VRING_NUM, ring); } > > > > > > +static void vhost_user_host_notifier_restore(struct vhost_dev *dev, > > > + int queue_idx) { > > > + struct vhost_user *u = dev->opaque; > > > + VhostUserHostNotifier *n = &u->user->notifier[queue_idx]; > > > + VirtIODevice *vdev = dev->vdev; > > > + > > > + if (n->addr && !n->set) { > > > + virtio_queue_set_host_notifier_mr(vdev, queue_idx, &n->mr, true); > > > + n->set = true; > > > + } > > > +} > > > + > > > +static void vhost_user_host_notifier_remove(struct vhost_dev *dev, > > > + int queue_idx) { > > > + struct vhost_user *u = dev->opaque; > > > + VhostUserHostNotifier *n = &u->user->notifier[queue_idx]; > > > + VirtIODevice *vdev = dev->vdev; > > > + > > > + if (n->addr && n->set) { > > > + virtio_queue_set_host_notifier_mr(vdev, queue_idx, &n->mr, > > > false); > > > + n->set = false; > > > + } > > > +} > > > + > > > static int vhost_user_set_vring_base(struct vhost_dev *dev, > > > struct vhost_vring_state > > > *ring) { > > > + vhost_user_host_notifier_restore(dev, ring->index); > > > + > > > return vhost_set_vring(dev, VHOST_USER_SET_VRING_BASE, ring); > > > } > > > > > > @@ -674,6 +712,8 @@ static int vhost_user_get_vring_base(struct > vhost_dev *dev, > > > .hdr.size = sizeof(msg.payload.state), > > > }; > > > > > > + vhost_user_host_notifier_remove(dev, ring->index); > > > + > > > if (vhost_user_write(dev, &msg, NULL, 0) < 0) { > > > return -1; > > > } > > > @@ -847,6 +887,76 @@ static int > vhost_user_slave_handle_config_change(struct vhost_dev *dev) > > > return ret; > > > } > > > > > > +static int vhost_user_slave_handle_vring_host_notifier(struct vhost_dev > *dev, > > > + > > > VhostUserVringArea *area, > > > + int fd) { > > > + int queue_idx = area->u64 & VHOST_USER_VRING_IDX_MASK; > > > + size_t page_size = qemu_real_host_page_size; > > > + struct vhost_user *u = dev->opaque; > > > + VhostUserState *user = u->user; > > > + VirtIODevice *vdev = dev->vdev; > > > + VhostUserHostNotifier *n; > > > + int ret = 0; > > > + void *addr; > > > + char *name; > > > + > > > + if (!virtio_has_feature(dev->protocol_features, > > > + VHOST_USER_PROTOCOL_F_HOST_NOTIFIER) || > > > + vdev == NULL || queue_idx >= virtio_get_num_queues(vdev)) { > > > + ret = -1; > > > + goto out; > > > + } > > > + > > > + n = &user->notifier[queue_idx]; > > > + > > > + if (n->addr) { > > > + virtio_queue_set_host_notifier_mr(vdev, queue_idx, &n->mr, > > > false); > > > + object_unparent(OBJECT(&n->mr)); > > > + munmap(n->addr, page_size); > > > + n->addr = NULL; > > > + } > > > + > > > + if (area->u64 & VHOST_USER_VRING_NOFD_MASK) { > > > + goto out; > > > + } > > > + > > > + /* Sanity check. */ > > > + if (area->size != page_size) { > > > + ret = -1; > > > + goto out; > > > + } > > > + > > > + addr = mmap(NULL, page_size, PROT_READ | PROT_WRITE, MAP_SHARED, > > > + fd, area->offset); > > > + if (addr == MAP_FAILED) { > > > + ret = -1; > > > + goto out; > > > + } > > > + > > > + name = g_strdup_printf("vhost-user/host-notifier@%p mmaps[%d]", > > > + user, queue_idx); > > > + memory_region_init_ram_device_ptr(&n->mr, OBJECT(vdev), name, > > > + page_size, addr); > > > + g_free(name); > > > + > > > + if (virtio_queue_set_host_notifier_mr(vdev, queue_idx, &n->mr, > > > true)) { > > > + munmap(addr, page_size); > > > + ret = -1; > > > + goto out; > > > + } > > > + > > > + n->addr = addr; > > > + n->set = true; > > > + > > > +out: > > > + /* Always close the fd. */ > > > + if (fd != -1) { > > > + close(fd); > > > + } > > > + return ret; > > > +} > > > + > > > static void slave_read(void *opaque) { > > > struct vhost_dev *dev = opaque; @@ -913,6 +1023,10 @@ static > > > void slave_read(void *opaque) > > > case VHOST_USER_SLAVE_CONFIG_CHANGE_MSG : > > > ret = vhost_user_slave_handle_config_change(dev); > > > break; > > > + case VHOST_USER_SLAVE_VRING_HOST_NOTIFIER_MSG: > > > + ret = vhost_user_slave_handle_vring_host_notifier(dev, > > > &payload.area, > > > + fd); > > > + break; > > > default: > > > error_report("Received unexpected msg type."); > > > if (fd != -1) { > > > @@ -1641,6 +1755,15 @@ VhostUserState *vhost_user_init(void) > > > > > > void vhost_user_cleanup(VhostUserState *user) { > > > + int i; > > > + > > > + for (i = 0; i < VIRTIO_QUEUE_MAX; i++) { > > > + if (user->notifier[i].addr) { > > > + object_unparent(OBJECT(&user->notifier[i].mr)); > > > + munmap(user->notifier[i].addr, qemu_real_host_page_size); > > > + user->notifier[i].addr = NULL; > > > + } > > > + } > > > } > > > > > > const VhostOps user_ops = { > > > diff --git a/include/hw/virtio/vhost-user.h > > > b/include/hw/virtio/vhost-user.h index eb8bc0d90d..fd660393a0 100644 > > > --- a/include/hw/virtio/vhost-user.h > > > +++ b/include/hw/virtio/vhost-user.h > > > @@ -9,9 +9,17 @@ > > > #define HW_VIRTIO_VHOST_USER_H > > > > > > #include "chardev/char-fe.h" > > > +#include "hw/virtio/virtio.h" > > > + > > > +typedef struct VhostUserHostNotifier { > > > + MemoryRegion mr; > > > + void *addr; > > > + bool set; > > > +} VhostUserHostNotifier; > > > > > > typedef struct VhostUserState { > > > CharBackend *chr; > > > + VhostUserHostNotifier notifier[VIRTIO_QUEUE_MAX]; > > > } VhostUserState; > > > > > > VhostUserState *vhost_user_init(void); > > > -- > > > 2.11.0