remove maps list from DMA controller (#674)

->maps existed so that if a consumer does vfu_map_sg() and then we are asked to
enable dirty page tracking, we won't mark those pages as dirty, and will hence
potentially lose data.

Now that we require quiesce and the use of either vfu_unmap_sg() or
vfu_sg_mark_dirty(), there's no need to have this list any more.

Signed-off-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Thanos Makatos <thanos.makatos@nutanix.com>

lib/dma.c

diff --git a/lib/dma.c b/lib/dma.c
index 2719639..daa1b58 100644
--- a/lib/dma.c
+++ b/lib/dma.c
@@ -99,7 +99,6 @@
     dma->nregions = 0;
     memset(dma->regions, 0, max_regions * sizeof(dma->regions[0]));
     dma->dirty_pgsize = 0;
-    LIST_INIT(&dma->maps);
 
     return dma;
 }
@@ -468,22 +467,6 @@
     return cnt;
 }
 
-static void
-dma_mark_dirty_sgs(dma_controller_t *dma)
-{
-    struct dma_sg *sg;
-
-    if (dma->dirty_pgsize == 0) {
-        return;
-    }
-
-    LIST_FOREACH(sg, &dma->maps, entry) {
-        if (sg->writeable) {
-            _dma_mark_dirty(dma, &dma->regions[sg->region], sg);
-        }
-    }
-}
-
 int
 dma_controller_dirty_page_logging_start(dma_controller_t *dma, size_t pgsize)
 {
@@ -523,8 +506,6 @@
     }
     dma->dirty_pgsize = pgsize;
 
-    dma_mark_dirty_sgs(dma);
-
     vfu_log(dma->vfu_ctx, LOG_DEBUG, "dirty pages: started logging");
 
     return 0;
@@ -628,8 +609,6 @@
 #endif
     memset(region->dirty_bitmap, 0, size);
 
-    dma_mark_dirty_sgs(dma);
-
     return 0;
 }
 

lib/dma.h

diff --git a/lib/dma.h b/lib/dma.h
index 6e31f15..aad3b9c 100644
--- a/lib/dma.h
+++ b/lib/dma.h
@@ -89,7 +89,6 @@
     uint64_t length;
     uint64_t offset;
     bool writeable;
-    LIST_ENTRY(dma_sg) entry;
 };
 
 typedef struct {
@@ -105,7 +104,6 @@
     int nregions;
     struct vfu_ctx *vfu_ctx;
     size_t dirty_pgsize;        // Dirty page granularity
-    LIST_HEAD(, dma_sg) maps;
     dma_memory_region_t regions[0];
 } dma_controller_t;
 
@@ -245,10 +243,6 @@
             return ERROR_INT(EFAULT);
         }
 
-        if (sg->writeable) {
-            LIST_INSERT_HEAD(&dma->maps, sg, entry);
-        }
-
         vfu_log(dma->vfu_ctx, LOG_DEBUG, "map %p-%p",
                 sg->dma_addr + sg->offset,
                 sg->dma_addr + sg->offset + sg->length);
@@ -294,30 +288,22 @@
 static inline void
 dma_unmap_sg(dma_controller_t *dma, dma_sg_t *sg, int cnt)
 {
+    dma_memory_region_t *region;
+
     assert(dma != NULL);
     assert(sg != NULL);
     assert(cnt > 0);
 
     do {
-        dma_memory_region_t *r;
-        /*
-         * FIXME this double loop will be removed if we replace the array with
-         * tfind(3)
-         */
-        for (r = dma->regions;
-             r < dma->regions + dma->nregions &&
-             r->info.iova.iov_base != sg->dma_addr;
-             r++);
-        if (r > dma->regions + dma->nregions) {
-            /* bad region */
-            continue;
+        if (sg->region >= dma->nregions) {
+            return;
         }
 
-        if (sg->writeable) {
-            LIST_REMOVE(sg, entry);
+        region = &dma->regions[sg->region];
 
+        if (sg->writeable) {
             if (dma->dirty_pgsize > 0) {
-                _dma_mark_dirty(dma, r, sg);
+                _dma_mark_dirty(dma, region, sg);
             }
         }
 

test/py/libvfio_user.py

diff --git a/test/py/libvfio_user.py b/test/py/libvfio_user.py
index ec9da7b..aeaefa5 100644
--- a/test/py/libvfio_user.py
+++ b/test/py/libvfio_user.py
@@ -547,8 +547,6 @@
         ("length", c.c_uint64),
         ("offset", c.c_uint64),
         ("writeable", c.c_bool),
-        ("le_next", c.c_void_p),
-        ("le_prev", c.c_void_p),
     ]
 
     def __str__(self):

test/py/test_dirty_pages.py

diff --git a/test/py/test_dirty_pages.py b/test/py/test_dirty_pages.py
index 9a0de3b..9f892bd 100644
--- a/test/py/test_dirty_pages.py
+++ b/test/py/test_dirty_pages.py
@@ -347,7 +347,7 @@
     vfu_unmap_sg(ctx, sg1, iovec1)
     vfu_unmap_sg(ctx, sg4, iovec4)
     bitmap = get_dirty_page_bitmap()
-    assert bitmap == 0b11110101
+    assert bitmap == 0b11110001
 
     # after another two unmaps, should just be one dirty page
     vfu_unmap_sg(ctx, sg2, iovec2)