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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.bie@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?
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
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