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

[Igor Mammedov <imammedo@redhat.com>]

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

>      }
> -    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

>      }
> -    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

> -        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) {