diff --git a/src/iov.c b/src/iov.c
index 76a3e54..9f9df91 100644
--- a/src/iov.c
+++ b/src/iov.c
@@ -39,6 +39,8 @@
 
 #include <assert.h>
 #include <string.h>
+#include <stdlib.h>
+#include <stdbool.h>
 #include "vrend_iov.h"
 
 size_t vrend_get_iovec_size(const struct iovec *iov, int iovlen) {
@@ -140,3 +142,63 @@ size_t vrend_read_from_iovec_cb(const struct iovec *iov, int iovlen,
 
 
 }
+
+/**
+ * Copy data from one iovec to another iovec.
+ *
+ * TODO: Implement iovec copy without copy to intermediate buffer.
+ *
+ * \param src_iov    The source iov.
+ * \param src_iovlen The number of memory regions in the source iov.
+ * \param src_offset The byte offset in the source iov to start reading from.
+ * \param dst_iov    The destination iov.
+ * \param dst_iovlen The number of memory regions in the destination iov.
+ * \param dst_offset The byte offset in the destination iov to start writing to.
+ * \param count      The number of bytes to copy
+ * \param buf        If not NULL, a pointer to a buffer of at least count size
+ *                   to use a temporary storage for the copy operation.
+ * \return           -1 on failure, 0 on success
+ */
+int vrend_copy_iovec(const struct iovec *src_iov, int src_iovlen, size_t src_offset,
+		     const struct iovec *dst_iov, int dst_iovlen, size_t dst_offset,
+		     size_t count, char *buf)
+{
+  int ret = 0;
+  bool needs_free;
+  size_t nread;
+  size_t nwritten;
+
+  if (src_iov == NULL || dst_iov == NULL)
+    return -1;
+
+  if (src_iov == dst_iov && src_offset == dst_offset)
+    return 0;
+
+  if (!buf) {
+    buf = malloc(count);
+    needs_free = true;
+  } else {
+    needs_free = false;
+  }
+
+  if (!buf)
+    return -1;
+
+  nread = vrend_read_from_iovec(src_iov, src_iovlen, src_offset, buf, count);
+  if (nread != count) {
+    ret = -1;
+    goto out;
+  }
+
+  nwritten = vrend_write_to_iovec(dst_iov, dst_iovlen, dst_offset, buf, count);
+  if (nwritten != count) {
+    ret = -1;
+    goto out;
+  }
+
+out:
+  if (needs_free)
+    free(buf);
+
+  return ret;
+}
diff --git a/src/vrend_iov.h b/src/vrend_iov.h
index 1d59e85..31341ca 100644
--- a/src/vrend_iov.h
+++ b/src/vrend_iov.h
@@ -46,4 +46,8 @@ size_t vrend_write_to_iovec(const struct iovec *iov, int iov_cnt,
 size_t vrend_read_from_iovec_cb(const struct iovec *iov, int iov_cnt,
                           size_t offset, size_t bytes, iov_cb iocb, void *cookie);
 
+int vrend_copy_iovec(const struct iovec *src_iov, int src_iovlen, size_t src_offset,
+                     const struct iovec *dst_iov, int dst_iovlen, size_t dst_offset,
+                     size_t count, char *buf);
+
 #endif
diff --git a/src/vrend_renderer.c b/src/vrend_renderer.c
index fa5ac97..9aac565 100644
--- a/src/vrend_renderer.c
+++ b/src/vrend_renderer.c
@@ -5818,7 +5818,7 @@ int vrend_renderer_resource_attach_iov(int res_handle, struct iovec *iov,
    res->iov = iov;
    res->num_iovs = num_iovs;
 
-   if (res->storage == VREND_RESOURCE_STORAGE_IOVEC) {
+   if (res->storage == VREND_RESOURCE_STORAGE_GUEST_ELSE_SYSTEM) {
       vrend_write_to_iovec(res->iov, res->num_iovs, 0,
             res->ptr, res->base.width0);
    }
@@ -5840,7 +5840,7 @@ void vrend_renderer_resource_detach_iov(int res_handle,
    if (num_iovs_p)
       *num_iovs_p = res->num_iovs;
 
-   if (res->storage == VREND_RESOURCE_STORAGE_IOVEC) {
+   if (res->storage == VREND_RESOURCE_STORAGE_GUEST_ELSE_SYSTEM) {
       vrend_read_from_iovec(res->iov, res->num_iovs, 0,
             res->ptr, res->base.width0);
    }
@@ -6154,7 +6154,7 @@ int vrend_renderer_resource_create(struct vrend_renderer_resource_create_args *a
    if (args->bind == VIRGL_BIND_CUSTOM) {
       assert(args->target == PIPE_BUFFER);
       /* use iovec directly when attached */
-      gr->storage = VREND_RESOURCE_STORAGE_IOVEC;
+      gr->storage = VREND_RESOURCE_STORAGE_GUEST_ELSE_SYSTEM;
       gr->ptr = malloc(args->width);
       if (!gr->ptr) {
          FREE(gr);
@@ -6225,7 +6225,7 @@ void vrend_renderer_resource_destroy(struct vrend_resource *res)
       if (res->tbo_tex_id)
          glDeleteTextures(1, &res->tbo_tex_id);
       break;
-   case VREND_RESOURCE_STORAGE_IOVEC:
+   case VREND_RESOURCE_STORAGE_GUEST_ELSE_SYSTEM:
       free(res->ptr);
       break;
    default:
@@ -6475,20 +6475,17 @@ static int vrend_renderer_transfer_write_iov(struct vrend_context *ctx,
 {
    void *data;
 
-   if (res->storage == VREND_RESOURCE_STORAGE_IOVEC) {
-      const bool need_write = (res->iov == NULL ||
-                               res->iov != iov ||
-                               info->offset != (size_t) info->box->x);
-      if (need_write) {
-         vrend_read_from_iovec(iov, num_iovs, info->offset,
-               res->ptr + info->box->x, info->box->width);
-
-         if (res->iov) {
-            vrend_write_to_iovec(res->iov, res->num_iovs, info->box->x,
-                  res->ptr + info->box->x, info->box->width);
-         }
-      }
+   if (res->storage == VREND_RESOURCE_STORAGE_GUEST ||
+       (res->storage == VREND_RESOURCE_STORAGE_GUEST_ELSE_SYSTEM && res->iov)) {
+      return vrend_copy_iovec(iov, num_iovs, info->offset,
+                              res->iov, res->num_iovs, info->box->x,
+                              info->box->width, res->ptr);
+   }
 
+   if (res->storage == VREND_RESOURCE_STORAGE_GUEST_ELSE_SYSTEM) {
+      assert(!res->iov);
+      vrend_read_from_iovec(iov, num_iovs, info->offset,
+                            res->ptr + info->box->x, info->box->width);
       return 0;
    }
 
@@ -7000,20 +6997,17 @@ static int vrend_renderer_transfer_send_iov(struct vrend_resource *res,
                                             struct iovec *iov, int num_iovs,
                                             const struct vrend_transfer_info *info)
 {
-   if (res->storage == VREND_RESOURCE_STORAGE_IOVEC) {
-      const bool need_send = (res->iov == NULL ||
-                              res->iov != iov ||
-                              info->offset != (size_t) info->box->x);
-      if (need_send) {
-         if (res->iov) {
-            vrend_read_from_iovec(res->iov, res->num_iovs, info->box->x,
-                  res->ptr + info->box->x, info->box->width);
-         }
-
-         vrend_write_to_iovec(iov, num_iovs, info->offset,
-               res->ptr + info->box->x, info->box->width);
-      }
+   if (res->storage == VREND_RESOURCE_STORAGE_GUEST ||
+       (res->storage == VREND_RESOURCE_STORAGE_GUEST_ELSE_SYSTEM && res->iov)) {
+      return vrend_copy_iovec(res->iov, res->num_iovs, info->box->x,
+                              iov, num_iovs, info->offset,
+                              info->box->width, res->ptr);
+   }
 
+   if (res->storage == VREND_RESOURCE_STORAGE_GUEST_ELSE_SYSTEM) {
+      assert(!res->iov);
+      vrend_write_to_iovec(iov, num_iovs, info->offset,
+                           res->ptr + info->box->x, info->box->width);
       return 0;
    }
 
@@ -8198,7 +8192,7 @@ int vrend_create_query(struct vrend_context *ctx, uint32_t handle,
    struct vrend_resource *res;
    uint32_t ret_handle;
    res = vrend_renderer_ctx_res_lookup(ctx, res_handle);
-   if (!res || res->storage != VREND_RESOURCE_STORAGE_IOVEC) {
+   if (!res || res->storage != VREND_RESOURCE_STORAGE_GUEST_ELSE_SYSTEM) {
       report_context_error(ctx, VIRGL_ERROR_CTX_ILLEGAL_RESOURCE, res_handle);
       return EINVAL;
    }
diff --git a/src/vrend_renderer.h b/src/vrend_renderer.h
index 24700c8..4ff7892 100644
--- a/src/vrend_renderer.h
+++ b/src/vrend_renderer.h
@@ -52,7 +52,11 @@ struct vrend_context;
 enum vrend_resource_storage_type {
    VREND_RESOURCE_STORAGE_TEXTURE,
    VREND_RESOURCE_STORAGE_BUFFER,
-   VREND_RESOURCE_STORAGE_IOVEC,
+   /* The resource contents are stored in shared guest memory. */
+   VREND_RESOURCE_STORAGE_GUEST,
+   /* The resource contents are stored in shared guest memory if it's
+    * attached, otherwise in host system memory. */
+   VREND_RESOURCE_STORAGE_GUEST_ELSE_SYSTEM,
 };
 
 struct vrend_resource {
@@ -71,7 +75,11 @@ struct vrend_resource {
    GLuint handle;
 
    void *priv;
+   /* Pointer to system memory storage for this resource. Only valid for
+    * VREND_RESOURCE_STORAGE_GUEST_ELSE_SYSTEM buffer storage.
+    */
    char *ptr;
+   /* IOV pointing to shared guest memory storage for this resource. */
    struct iovec *iov;
    uint32_t num_iovs;
    uint64_t mipmap_offsets[VR_MAX_TEXTURE_2D_LEVELS];