Re: [Qemu-devel] [PATCH v4 2/6] vhost: Simplify ring verification checks

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Igor Mammedov (imammedo@redhat.com) wrote:
> On Wed, 13 Dec 2017 18:08:03 +0000
> "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com> wrote:
> 
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > 
> > vhost_verify_ring_mappings() were used to verify that
> > rings are still accessible and related memory hasn't
> > been moved after flatview is updated.
> > 
> > It was doing checks by mapping ring's GPA+len and
> > checking that HVA hadn't changed with new memory map.
> > To avoid maybe expensive mapping call, we were
> > identifying address range that changed and were doing
> > mapping only if ring was in changed range.
> > 
> > However it's not neccessary to perform ring's GPA
> > mapping as we already have its current HVA and all
> > we need is to verify that ring's GPA translates to
> > the same HVA in updated flatview.
> > 
> > This will allow the following patches to simplify the range
> > comparison that was previously needed to avoid expensive
> > verify_ring_mapping calls.
> > 
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > with modifications by:
> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > ---
> >  hw/virtio/vhost.c | 74 ++++++++++++++++++++++++++++++-------------------------
> >  1 file changed, 41 insertions(+), 33 deletions(-)
> > 
> > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> > index e923219e63..c7ce7baf9b 100644
> > --- a/hw/virtio/vhost.c
> > +++ b/hw/virtio/vhost.c
> > @@ -450,35 +450,37 @@ static void vhost_memory_unmap(struct vhost_dev *dev, void *buffer,
> >      }
> >  }
> >  
> > -static int vhost_verify_ring_part_mapping(struct vhost_dev *dev,
> > -                                          void *part,
> > -                                          uint64_t part_addr,
> > -                                          uint64_t part_size,
> > -                                          uint64_t start_addr,
> > -                                          uint64_t size)
> > +static int vhost_verify_ring_part_mapping(void *ring_hva,
> > +                                          uint64_t ring_gpa,
> > +                                          uint64_t ring_size,
> > +                                          void *reg_hva,
> > +                                          uint64_t reg_gpa,
> > +                                          uint64_t reg_size)
> >  {
> > -    hwaddr l;
> > -    void *p;
> > -    int r = 0;
> > +    uint64_t hva_ring_offset;
> > +    uint64_t ring_last = range_get_last(ring_gpa, ring_size);
> > +    uint64_t reg_last = range_get_last(reg_gpa, reg_size);
> >  
> > -    if (!ranges_overlap(start_addr, size, part_addr, part_size)) {
> > +    if (ring_last < reg_gpa || ring_gpa > reg_last) {
> >          return 0;
> >      }
> > -    l = part_size;
> > -    p = vhost_memory_map(dev, part_addr, &l, 1);
> > -    if (!p || l != part_size) {
> > -        r = -ENOMEM;
> > +    /* check that whole ring's is mapped */
> > +    if (ring_last > reg_last) {
> > +        return -EBUSY;
> ENOMEM

Done

> >      }
> > -    if (p != part) {
> > -        r = -EBUSY;
> > +    /* check that ring's MemoryRegion wasn't replaced */
> > +    hva_ring_offset = ring_gpa - reg_gpa;
> > +    if (ring_hva != reg_hva + hva_ring_offset) {
> > +        return -ENOMEM;
> EBUSY

Done

> 
> >      }
> > -    vhost_memory_unmap(dev, p, l, 0, 0);
> > -    return r;
> > +
> > +    return 0;
> >  }
> >  
> >  static int vhost_verify_ring_mappings(struct vhost_dev *dev,
> > -                                      uint64_t start_addr,
> > -                                      uint64_t size)
> > +                                      void *reg_hva,
> > +                                      uint64_t reg_gpa,
> > +                                      uint64_t reg_size)
> >  {
> >      int i, j;
> >      int r = 0;
> > @@ -492,22 +494,25 @@ static int vhost_verify_ring_mappings(struct vhost_dev *dev,
> >          struct vhost_virtqueue *vq = dev->vqs + i;
> >  
> >          j = 0;
> > -        r = vhost_verify_ring_part_mapping(dev, vq->desc, vq->desc_phys,
> > -                                           vq->desc_size, start_addr, size);
> > +        r = vhost_verify_ring_part_mapping(
> > +                vq->desc, vq->desc_phys, vq->desc_size,
> > +                reg_hva, reg_gpa, reg_size);
> >          if (r) {
> >              break;
> >          }
> >  
> >          j++;
> > -        r = vhost_verify_ring_part_mapping(dev, vq->avail, vq->avail_phys,
> > -                                           vq->avail_size, start_addr, size);
> > +        r = vhost_verify_ring_part_mapping(
> > +                vq->desc, vq->desc_phys, vq->desc_size,
> > +                reg_hva, reg_gpa, reg_size);
> >          if (r) {
> >              break;
> >          }
> >  
> >          j++;
> > -        r = vhost_verify_ring_part_mapping(dev, vq->used, vq->used_phys,
> > -                                           vq->used_size, start_addr, size);
> > +        r = vhost_verify_ring_part_mapping(
> > +                vq->desc, vq->desc_phys, vq->desc_size,
> > +                reg_hva, reg_gpa, reg_size);
> >          if (r) {
> >              break;
> >          }
> > @@ -633,8 +638,6 @@ static void vhost_commit(MemoryListener *listener)
> >  {
> >      struct vhost_dev *dev = container_of(listener, struct vhost_dev,
> >                                           memory_listener);
> > -    hwaddr start_addr = 0;
> > -    ram_addr_t size = 0;
> >      uint64_t log_size;
> >      int r;
> >  
> > @@ -649,11 +652,16 @@ static void vhost_commit(MemoryListener *listener)
> >      }
> >  
> >      if (dev->started) {
> ^^^ not needed as we bail out earlier if it's not true

Done

> > -        start_addr = dev->mem_changed_start_addr;
> > -        size = dev->mem_changed_end_addr - dev->mem_changed_start_addr + 1;
> > -
> > -        r = vhost_verify_ring_mappings(dev, start_addr, size);
> > -        assert(r >= 0);
> > +        int i;
> > +        for (i = 0; i < dev->mem->nregions; i++) {
> > +            if (vhost_verify_ring_mappings(dev,
> > +                               (void *)dev->mem->regions[i].userspace_addr,
> > +                               dev->mem->regions[i].guest_phys_addr,
> > +                               dev->mem->regions[i].memory_size)) {
> > +                error_report("Verify ring failure on region %d", i);
> > +                abort();
> > +            }
> > +        }
> >      }
> >  
> >      if (!dev->log_enabled) {
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK