Re: [Qemu-devel] [RFC] vhost: check if ring mapping is still valid when building memmap

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

* Igor Mammedov (imammedo@redhat.com) wrote:
> vhost_verify_ring_mappings() were used to verify that
> rings are still accessible and related memory hasn't
> been moved after flatview is updated.

I think I've rolled the equivalent into my v2 I've just
posted; please have a look.

Dave

> It were doing checks by mapping ring's GPA+len and
> checking that HVA hasn'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 were in changed range.
> 
> However it's no neccessary to perform ringi's GPA
> mapping as we already have it's current HVA and all
> we need is to verify that ring's GPA translates to
> the same HVA in updated flatview.
> 
> That could be done during time when we are building
> vhost memmap where vhost_update_mem_cb() already maps
> every RAM MemoryRegionSection to get section HVA. This
> fact can be used to check that ring belongs to the same
> MemoryRegion in the same place, like this:
> 
>   hva_ring_offset = GPA(ring) - GPA(MemoryRegionSection)
>   ring_hva == HVA(MemoryRegionSection) + hva_ring_offset
> 
> Doing this would allow us to drop ~100LOC of code which
> figures out changed memory range and avoid calling not
> needed reverse vhost_memory_map(is_write=true) which is
> overkill for the task at hand.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
> PS:
>    should be applied on top of David's series
> 
> ---
>  include/hw/virtio/vhost.h |   2 -
>  hw/virtio/vhost.c         | 195 ++++++++++++++--------------------------------
>  2 files changed, 57 insertions(+), 140 deletions(-)
> 
> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
> index 467dc77..fc4af5c 100644
> --- a/include/hw/virtio/vhost.h
> +++ b/include/hw/virtio/vhost.h
> @@ -68,8 +68,6 @@ struct vhost_dev {
>      uint64_t log_size;
>      Error *migration_blocker;
>      bool memory_changed;
> -    hwaddr mem_changed_start_addr;
> -    hwaddr mem_changed_end_addr;
>      const VhostOps *vhost_ops;
>      void *opaque;
>      struct vhost_log *log;
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 5b9a7d7..026bac3 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -296,35 +296,43 @@ 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)) {
> +    /* start check from the end so that the rest of checks
> +     * are done when whole ring is in merged sections range
> +     */
> +    if (ring_last < reg_last || 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 (range_get_last(ring_gpa, ring_size) >
> +        range_get_last(reg_gpa, reg_size)) {
> +        return -EBUSY;
>      }
> -    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;
>      }
> -    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;
> @@ -338,23 +346,26 @@ 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);
> -        if (!r) {
> +        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);
> -        if (!r) {
> +        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);
> -        if (!r) {
> +        r = vhost_verify_ring_part_mapping(
> +                vq->desc, vq->desc_phys, vq->desc_size,
> +                reg_hva, reg_gpa, reg_size);
> +        if (r) {
>              break;
>          }
>      }
> @@ -384,24 +395,18 @@ static bool vhost_section(MemoryRegionSection *section)
>      return result;
>  }
>  
> -static void vhost_begin(MemoryListener *listener)
> -{
> -    struct vhost_dev *dev = container_of(listener, struct vhost_dev,
> -                                         memory_listener);
> -    dev->mem_changed_end_addr = 0;
> -    dev->mem_changed_start_addr = -1;
> -}
> -
>  struct vhost_update_mem_tmp {
>      struct vhost_dev   *dev;
>      uint32_t nregions;
>      struct vhost_memory_region *regions;
>  };
>  
> +
>  /* Called for each MRS from vhost_update_mem */
>  static int vhost_update_mem_cb(MemoryRegionSection *mrs, void *opaque)
>  {
>      struct vhost_update_mem_tmp *vtmp = opaque;
> +    struct vhost_dev   *dev = vtmp->dev;
>      struct vhost_memory_region *cur_vmr;
>      bool need_add = true;
>      uint64_t mrs_size;
> @@ -416,8 +421,7 @@ static int vhost_update_mem_cb(MemoryRegionSection *mrs, void *opaque)
>      mrs_host = (uintptr_t)memory_region_get_ram_ptr(mrs->mr) +
>                           mrs->offset_within_region;
>  
> -    trace_vhost_update_mem_cb(mrs->mr->name, mrs_gpa, mrs_size,
> -                              (uint64_t)mrs_host);
> +    trace_vhost_update_mem_cb(mrs->mr->name, mrs_gpa, mrs_size, mrs_host);
>  
>      if (vtmp->nregions) {
>          /* Since we already have at least one region, lets see if
> @@ -459,85 +463,19 @@ static int vhost_update_mem_cb(MemoryRegionSection *mrs, void *opaque)
>          cur_vmr->flags_padding = 0;
>      }
>  
> -    return 0;
> -}
> -
> -static bool vhost_update_compare_list(struct vhost_dev *dev,
> -                                      struct vhost_update_mem_tmp *vtmp,
> -                                      hwaddr *change_start, hwaddr *change_end)
> -{
> -    uint32_t oldi, newi;
> -    *change_start = 0;
> -    *change_end = 0;
> -
> -    for (newi = 0, oldi = 0; newi < vtmp->nregions; newi++) {
> -        struct vhost_memory_region *newr = &vtmp->regions[newi];
> -        hwaddr newr_last = range_get_last(newr->guest_phys_addr,
> -                                          newr->memory_size);
> -        trace_vhost_update_compare_list_loopn(newi, oldi,
> -                                        newr->guest_phys_addr,
> -                                        newr->memory_size);
> -        bool whole_change = true;
> -        while (oldi < dev->mem->nregions) {
> -            struct vhost_memory_region *oldr = &dev->mem->regions[oldi];
> -            hwaddr oldr_last = range_get_last(oldr->guest_phys_addr,
> -                                          oldr->memory_size);
> -            trace_vhost_update_compare_list_loopo(newi, oldi,
> -                                        oldr->guest_phys_addr,
> -                                        oldr->memory_size);
> -            if (newr->guest_phys_addr == oldr->guest_phys_addr &&
> -                newr->memory_size == oldr->memory_size) {
> -                /* Match in GPA and size, but it could be different
> -                 * in host address or flags
> -                 */
> -                whole_change = newr->userspace_addr != oldr->userspace_addr ||
> -                               newr->flags_padding != oldr->flags_padding;
> -                oldi++;
> -                break; /* inner old loop */
> -            }
> -            /* There's a difference - need to figure out what */
> -            if (oldr_last < newr->guest_phys_addr) {
> -                /* There used to be a region before us that's gone */
> -                *change_start = MIN(*change_start, oldr->guest_phys_addr);
> -                *change_end = MAX(*change_end, oldr_last);
> -                oldi++;
> -                continue; /* inner old loop */
> -            }
> -            if (oldr->guest_phys_addr > newr_last) {
> -                /* We've passed all the old mappings that could have overlapped
> -                 * this one
> -                 */
> -                break; /* Inner old loop */
> -            }
> -            /* Overlap case */
> -            *change_start = MIN(*change_start,
> -                                MIN(oldr->guest_phys_addr,
> -                                    newr->guest_phys_addr));
> -            *change_end = MAX(*change_end,
> -                                MAX(oldr_last, newr_last));
> -            whole_change = false;
> -            /* There might be more old mappings that overlap */
> -            oldi++;
> -        }
> -        if (whole_change) {
> -            /* No old region to compare against, this must be a change */
> -            *change_start = MIN(*change_start, newr->guest_phys_addr);
> -            *change_end = MAX(*change_end, newr_last);
> -        }
> +    if (dev->started &&
> +        vhost_verify_ring_mappings(dev, (void *)mrs_host, mrs_gpa, mrs_size)) {
> +        abort();
>      }
>  
> -    return *change_start || *change_end;
> +    return 0;
>  }
>  
>  static int vhost_update_mem(struct vhost_dev *dev)
>  {
>      int res;
> -    struct vhost_update_mem_tmp vtmp;
> -    hwaddr change_start, change_end;
> -    bool need_update;
> -    vtmp.regions = 0;
> -    vtmp.nregions = 0;
> -    vtmp.dev = dev;
> +    size_t mem_size;
> +    struct vhost_update_mem_tmp vtmp = {.dev = dev};
>  
>      res = address_space_iterate(&address_space_memory,
>                                  vhost_update_mem_cb, &vtmp);
> @@ -545,24 +483,17 @@ static int vhost_update_mem(struct vhost_dev *dev)
>          goto out;
>      }
>  
> -    need_update = vhost_update_compare_list(dev, &vtmp,
> -                                            &change_start, &change_end);
> -    trace_vhost_update_mem_comparison(need_update,
> -                                      (uint64_t)change_start,
> -                                      (uint64_t)change_end);
> -    if (need_update) {
> -        /* Update the main regions list from our tmp */
> -        size_t mem_size = offsetof(struct vhost_memory, regions) +
> -            (vtmp.nregions + 1) * sizeof dev->mem->regions[0];
> +    mem_size = offsetof(struct vhost_memory, regions) +
> +               (vtmp.nregions + 1) * sizeof dev->mem->regions[0];
>  
> +    if(vtmp.nregions != dev->mem->nregions ||
> +       memcmp(vtmp.regions, dev->mem->regions, mem_size)) {
> +        /* Update the main regions list from our tmp */
>          dev->mem = g_realloc(dev->mem, mem_size);
>          dev->mem->nregions = vtmp.nregions;
>          memcpy(dev->mem->regions, vtmp.regions,
>                 vtmp.nregions * sizeof dev->mem->regions[0]);
>          used_memslots = vtmp.nregions;
> -
> -        dev->mem_changed_start_addr = change_start;
> -        dev->mem_changed_end_addr = change_end;
>      }
>  
>  out:
> @@ -574,8 +505,6 @@ 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;
>  
> @@ -585,22 +514,11 @@ static void vhost_commit(MemoryListener *listener)
>      if (!dev->started) {
>          return;
>      }
> -    if (dev->mem_changed_start_addr > dev->mem_changed_end_addr) {
> -        return;
> -    }
>  
>      if (vhost_update_mem(dev)) {
>          return;
>      }
>  
> -    if (dev->started) {
> -        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);
> -    }
> -
>      if (!dev->log_enabled) {
>          r = dev->vhost_ops->vhost_set_mem_table(dev, dev->mem);
>          if (r < 0) {
> @@ -1235,7 +1153,6 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
>      hdev->features = features;
>  
>      hdev->memory_listener = (MemoryListener) {
> -        .begin = vhost_begin,
>          .commit = vhost_commit,
>          .region_add = vhost_region_add,
>          .region_del = vhost_region_del,
> @@ -1458,7 +1375,6 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev)
>      /* should only be called after backend is connected */
>      assert(hdev->vhost_ops);
>  
> -    hdev->started = true;
>      hdev->vdev = vdev;
>  
>      r = vhost_dev_set_features(hdev, hdev->log_enabled);
> @@ -1469,6 +1385,9 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev)
>      if (vhost_update_mem(hdev)) {
>          goto fail_mem;
>      }
> +
> +    hdev->started = true;
> +
>      if (vhost_dev_has_iommu(hdev)) {
>          memory_listener_register(&hdev->iommu_listener, vdev->dma_as);
>      }
> -- 
> 2.7.4
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK