Re: [Qemu-devel] [PATCH v3 21/29] vhost+postcopy: Add vhost waker

[Dr. David Alan Gilbert]

* Peter Xu (address@hidden) wrote:
> On Fri, Feb 16, 2018 at 01:16:17PM +0000, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <address@hidden>
> > 
> > Register a waker function in vhost-user code to be notified when
> > pages arrive or requests to previously mapped pages get requested.
> > 
> > Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> > ---
> >  hw/virtio/trace-events |  3 +++
> >  hw/virtio/vhost-user.c | 30 ++++++++++++++++++++++++++++++
> >  2 files changed, 33 insertions(+)
> > 
> > diff --git a/hw/virtio/trace-events b/hw/virtio/trace-events
> > index 3afd12cfea..fe5e0ff856 100644
> > --- a/hw/virtio/trace-events
> > +++ b/hw/virtio/trace-events
> > @@ -13,6 +13,9 @@ vhost_user_postcopy_fault_handler_found(int i, uint64_t 
> > region_offset, uint64_t
> >  vhost_user_postcopy_listen(void) ""
> >  vhost_user_set_mem_table_postcopy(uint64_t client_addr, uint64_t qhva, int 
> > reply_i, int region_i) "client:0x%"PRIx64" for hva: 0x%"PRIx64" reply %d 
> > region %d"
> >  vhost_user_set_mem_table_withfd(int index, const char *name, uint64_t 
> > memory_size, uint64_t guest_phys_addr, uint64_t userspace_addr, uint64_t 
> > offset) "%d:%s: size:0x%"PRIx64" GPA:0x%"PRIx64" QVA/userspace:0x%"PRIx64" 
> > RB offset:0x%"PRIx64
> > +vhost_user_postcopy_waker(const char *rb, uint64_t rb_offset) "%s + 
> > 0x%"PRIx64
> > +vhost_user_postcopy_waker_found(uint64_t client_addr) "0x%"PRIx64
> > +vhost_user_postcopy_waker_nomatch(const char *rb, uint64_t rb_offset) "%s 
> > + 0x%"PRIx64
> >  
> >  # hw/virtio/virtio.c
> >  virtqueue_alloc_element(void *elem, size_t sz, unsigned in_num, unsigned 
> > out_num) "elem %p size %zd in_num %u out_num %u"
> > diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> > index 4589bfd92e..74807091a0 100644
> > --- a/hw/virtio/vhost-user.c
> > +++ b/hw/virtio/vhost-user.c
> > @@ -990,6 +990,35 @@ static int vhost_user_postcopy_fault_handler(struct 
> > PostCopyFD *pcfd,
> >      return -1;
> >  }
> >  
> > +static int vhost_user_postcopy_waker(struct PostCopyFD *pcfd, RAMBlock *rb,
> > +                                     uint64_t offset)
> > +{
> > +    struct vhost_dev *dev = pcfd->data;
> > +    struct vhost_user *u = dev->opaque;
> > +    int i;
> > +
> > +    trace_vhost_user_postcopy_waker(qemu_ram_get_idstr(rb), offset);
> > +
> > +    if (!u) {
> > +        return 0;
> > +    }
> > +    /* Translate the offset into an address in the clients address space */
> > +    for (i = 0; i < MIN(dev->mem->nregions, u->region_rb_len); i++) {
> > +        if (u->region_rb[i] == rb &&
> > +            offset >= u->region_rb_offset[i] &&
> > +            offset < (u->region_rb_offset[i] +
> > +                      dev->mem->regions[i].memory_size)) {
> > +            uint64_t client_addr = (offset - u->region_rb_offset[i]) +
> > +                                   u->postcopy_client_bases[i];
> > +            trace_vhost_user_postcopy_waker_found(client_addr);
> > +            return postcopy_wake_shared(pcfd, client_addr, rb);
> > +        }
> > +    }
> > +
> > +    trace_vhost_user_postcopy_waker_nomatch(qemu_ram_get_idstr(rb), 
> > offset);
> > +    return 0;
> 
> Can we really reach here?

Yes; note that all the waker's registered get called for all pages
received
so that:
  a) A page not in shared memory, or not actually registered with a
device, still calls the waker's and it's upto the waker to figure out
whether it's interested for the device it belongs to.

  b) With two devices registered, they might each have registered
different areas of shared memory, and thus it's upto the waker to figure
out if it's interested in this specific page.

Dave

> > +}
> > +
> >  /*
> >   * Called at the start of an inbound postcopy on reception of the
> >   * 'advise' command.
> > @@ -1035,6 +1064,7 @@ static int vhost_user_postcopy_advise(struct 
> > vhost_dev *dev, Error **errp)
> >      u->postcopy_fd.fd = ufd;
> >      u->postcopy_fd.data = dev;
> >      u->postcopy_fd.handler = vhost_user_postcopy_fault_handler;
> > +    u->postcopy_fd.waker = vhost_user_postcopy_waker;
> >      u->postcopy_fd.idstr = "vhost-user"; /* Need to find unique name */
> >      postcopy_register_shared_ufd(&u->postcopy_fd);
> >      return 0;
> > -- 
> > 2.14.3
> > 
> 
> Thanks,
> 
> -- 
> Peter Xu
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK