Re: [Qemu-devel] [PATCH v4 4/6] vhost: add regions to temporary list

[Dr. David Alan Gilbert]

* Igor Mammedov (address@hidden) wrote:
> On Wed, 13 Dec 2017 18:08:05 +0000
> "Dr. David Alan Gilbert (git)" <address@hidden> wrote:
> 
> > From: "Dr. David Alan Gilbert" <address@hidden>
> > 
> > As regions are reported by the listener to the _nop and _add
> > methods, add them to our new temporary list.
> > Regions that abut can be merged if the backend allows.
> > 
> > Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> > ---
> >  hw/virtio/trace-events |  2 ++
> >  hw/virtio/vhost.c      | 70 
> > ++++++++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 72 insertions(+)
> > 
> > diff --git a/hw/virtio/trace-events b/hw/virtio/trace-events
> > index 4a493bcd46..7de0663652 100644
> > --- a/hw/virtio/trace-events
> > +++ b/hw/virtio/trace-events
> > @@ -1,6 +1,8 @@
> >  # See docs/devel/tracing.txt for syntax documentation.
> >  
> >  # hw/virtio/vhost.c
> > +vhost_region_add_tmp(const char *name, uint64_t gpa, uint64_t size, 
> > uint64_t host) "%s: 0x%"PRIx64"+0x%"PRIx64" @ 0x%"PRIx64
> > +vhost_region_add_tmp_abut(const char *name, uint64_t new_size) "%s: 
> > 0x%"PRIx64
> >  vhost_section(const char *name, int r) "%s:%d"
> >  
> >  # hw/virtio/virtio.c
> > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> > index 4523f45587..2084888aa7 100644
> > --- a/hw/virtio/vhost.c
> > +++ b/hw/virtio/vhost.c
> > @@ -694,6 +694,67 @@ static void vhost_commit(MemoryListener *listener)
> >      dev->memory_changed = false;
> >  }
> >  
> > +/* Adds the section data to the tmp_mem structure.
> > + * It relies on the listener calling us in memory address order
> > + * and for each region (via the _add and _nop methods).
> > + */
> > +static void vhost_region_add_tmp(struct vhost_dev *dev,
> > +                                 MemoryRegionSection *section)
> > +{
> > +    bool need_add = true;
> > +    uint64_t mrs_size = int128_get64(section->size);
> > +    uint64_t mrs_gpa = section->offset_within_address_space;
> > +    uintptr_t mrs_host = (uintptr_t)memory_region_get_ram_ptr(section->mr) 
> > +
> > +                         section->offset_within_region;
> > +
> > +    trace_vhost_region_add_tmp(section->mr->name, mrs_gpa, mrs_size, 
> > mrs_host);
> > +
> > +    if (dev->tmp_mem->nregions) {
> > +        /* Since we already have at least one region, lets see if
> > +         * this extends it; since we're scanning in order, we only
> > +         * have to look at the last one, and the FlatView that calls
> > +         * us shouldn't have overlaps.
> > +         */
> > +        struct vhost_memory_region *prev_vmr = dev->tmp_mem->regions +
> > +                                               (dev->tmp_mem->nregions - 
> > 1);
> > +        uint64_t prev_gpa_start = prev_vmr->guest_phys_addr;
> > +        uint64_t prev_gpa_end   = range_get_last(prev_gpa_start,
> > +                                                 prev_vmr->memory_size);
> > +        uint64_t prev_host_start = prev_vmr->userspace_addr;
> > +        uint64_t prev_host_end   = range_get_last(prev_host_start,
> > +                                                  prev_vmr->memory_size);
> > +
> > +        if (prev_gpa_end + 1 == mrs_gpa &&
> > +            prev_host_end + 1 == mrs_host &&
> > +            (!dev->vhost_ops->vhost_backend_can_merge ||
> > +                dev->vhost_ops->vhost_backend_can_merge(dev,
> > +                    mrs_host, mrs_size,
> > +                    prev_host_start, prev_vmr->memory_size))) {
> > +            /* The two regions abut */
> > +            need_add = false;
> > +            mrs_size = mrs_size + prev_vmr->memory_size;
> > +            prev_vmr->memory_size = mrs_size;
> > +            trace_vhost_region_add_tmp_abut(section->mr->name, mrs_size);
> > +        }
> > +    }
> > +
> > +    if (need_add) {
> > +        uint32_t nregions = dev->tmp_mem->nregions;
> > +        size_t s = offsetof(struct vhost_memory, regions) +
> > +                            (nregions + 1) * sizeof 
> > dev->tmp_mem->regions[0];
> > +        dev->tmp_mem = g_realloc(dev->tmp_mem, s);
> > +        dev->tmp_mem->nregions++;
> > +        struct vhost_memory_region *cur_vmr = 
> > &dev->tmp_mem->regions[nregions];
> > +
> > +        cur_vmr->guest_phys_addr = mrs_gpa;
> > +        cur_vmr->memory_size     = mrs_size;
> > +        cur_vmr->userspace_addr  = mrs_host;
> > +        cur_vmr->flags_padding = 0;
> > +    }
> > +
> > +
> > +}
> > +
> >  static void vhost_region_add(MemoryListener *listener,
> >                               MemoryRegionSection *section)
> >  {
> > @@ -703,6 +764,7 @@ static void vhost_region_add(MemoryListener *listener,
> >      if (!vhost_section(section)) {
> >          return;
> >      }
> > +    vhost_region_add_tmp(dev, section);
> >  
> >      ++dev->n_mem_sections;
> >      dev->mem_sections = g_renew(MemoryRegionSection, dev->mem_sections,
> > @@ -800,9 +862,17 @@ static void vhost_iommu_region_del(MemoryListener 
> > *listener,
> >      }
> >  }
> >  
> > +/* Called on regions that have not changed */
> >  static void vhost_region_nop(MemoryListener *listener,
> >                               MemoryRegionSection *section)
> >  {
> move it close to add/del callbacks
> 
> > +    struct vhost_dev *dev = container_of(listener, struct vhost_dev,
> > +                                         memory_listener);
> > +    if (!vhost_section(section)) {
> > +        return;
> > +    }
> > +
> > +    vhost_region_add_tmp(dev, section);
> if you'd operate on temporary mem_sections,
> I'd add memory_region_ref() and get rid of region_del callback
> with its section lookup, by unreffing old sections at commit time.
> 
> Also it seems that we have a race in current code where
> region_del() unrefs memory region first and then by the
> commit time memory region could be gone since old flatview
> is unreffed before commit callback is called, but guest still
> uses old memory map until vhost_set_mem_table() is complete.
> We probably should unref deleted(old) sections after
> guest gets new memmap.

Will they really get cleaned up before the commit() returns?
There's no rcu like thing guarding it?

Dave

> 
> >  }
> >  
> >  static int vhost_virtqueue_set_addr(struct vhost_dev *dev,
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK