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

[Igor Mammedov]

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 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 <address@hidden>
---
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