winsys/svga: Optionally avoid caching buffer maps

Mapping of graphics kernel buffers is quite costly. Therefore the svga
drm winsys caches all kernel buffer maps. However, that may lead to
less testing coverage of the unmap paths and (possibly) processes running
out of virtual memory space. Introduce a possibility to avoid that caching
by setting the environment variable SVGA_FORCE_KERNEL_UNMAPS to 1.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Reviewed-by: Matthew McClure <mcclurem@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4804>

src/gallium/winsys/svga/drm/vmw_buffer.c

@@ -63,6 +63,7 @@ struct vmw_gmr_buffer
    struct vmw_region *region;
    void *map;
    unsigned map_flags;
+   unsigned map_count;
 };
 
 
@@ -104,8 +105,12 @@ vmw_gmr_buffer_destroy(struct pb_buffer *_buf)
 {
    struct vmw_gmr_buffer *buf = vmw_gmr_buffer(_buf);
 
-   vmw_ioctl_region_unmap(buf->region);
-   
+   assert(buf->map_count == 0);
+   if (buf->map) {
+      assert(buf->mgr->vws->cache_maps);
+      vmw_ioctl_region_unmap(buf->region);
+   }
+
    vmw_ioctl_region_destroy(buf->region);
 
    FREE(buf);
@@ -126,7 +131,6 @@ vmw_gmr_buffer_map(struct pb_buffer *_buf,
    if (!buf->map)
       return NULL;
 
-
    if ((_buf->usage & VMW_BUFFER_USAGE_SYNC) &&
        !(flags & PB_USAGE_UNSYNCHRONIZED)) {
       ret = vmw_ioctl_syncforcpu(buf->region,
@@ -137,6 +141,7 @@ vmw_gmr_buffer_map(struct pb_buffer *_buf,
          return NULL;
    }
 
+   buf->map_count++;
    return buf->map;
 }
 
@@ -153,6 +158,12 @@ vmw_gmr_buffer_unmap(struct pb_buffer *_buf)
                                !(flags & PB_USAGE_CPU_WRITE),
                                FALSE);
    }
+
+   assert(buf->map_count > 0);
+   if (!--buf->map_count && !buf->mgr->vws->cache_maps) {
+      vmw_ioctl_region_unmap(buf->region);
+      buf->map = NULL;
+   }
 }
 
 

src/gallium/winsys/svga/drm/vmw_screen.c

@@ -67,6 +67,7 @@ vmw_winsys_create( int fd )
 {
    struct vmw_winsys_screen *vws;
    struct stat stat_buf;
+   const char *getenv_val;
 
    if (dev_hash == NULL) {
       dev_hash = _mesa_hash_table_create(NULL, vmw_dev_hash, vmw_dev_compare);
@@ -97,6 +98,8 @@ vmw_winsys_create( int fd )
    vws->base.have_gb_dma = !vws->force_coherent;
    vws->base.need_to_rebind_resources = FALSE;
    vws->base.have_transfer_from_buffer_cmd = vws->base.have_vgpu10;
+   getenv_val = getenv("SVGA_FORCE_KERNEL_UNMAPS");
+   vws->cache_maps = !getenv_val || strcmp(getenv_val, "0") == 0;
    vws->fence_ops = vmw_fence_ops_create(vws);
    if (!vws->fence_ops)
       goto out_no_fence_ops;

src/gallium/winsys/svga/drm/vmw_screen.h

@@ -108,6 +108,7 @@ struct vmw_winsys_screen
    mtx_t cs_mutex;
 
    boolean force_coherent;
+   boolean cache_maps;
 };
 
 

src/gallium/winsys/svga/drm/vmw_screen_ioctl.c

@@ -64,7 +64,6 @@ struct vmw_region
    uint32_t handle;
    uint64_t map_handle;
    void *data;
-   uint32_t map_count;
    int drm_fd;
    uint32_t size;
 };
@@ -637,7 +636,6 @@ vmw_ioctl_region_create(struct vmw_winsys_screen *vws, uint32_t size)
    region->data = NULL;
    region->handle = rep->handle;
    region->map_handle = rep->map_handle;
-   region->map_count = 0;
    region->size = size;
    region->drm_fd = vws->ioctl.drm_fd;
 
@@ -659,10 +657,7 @@ vmw_ioctl_region_destroy(struct vmw_region *region)
    vmw_printf("%s: gmrId = %u, offset = %u\n", __FUNCTION__,
               region->ptr.gmrId, region->ptr.offset);
 
-   if (region->data) {
-      os_munmap(region->data, region->size);
-      region->data = NULL;
-   }
+   assert(region->data == NULL);
 
    memset(&arg, 0, sizeof(arg));
    arg.handle = region->handle;
@@ -701,8 +696,6 @@ vmw_ioctl_region_map(struct vmw_region *region)
       region->data = map;
    }
 
-   ++region->map_count;
-
    return region->data;
 }
 
@@ -711,7 +704,9 @@ vmw_ioctl_region_unmap(struct vmw_region *region)
 {
    vmw_printf("%s: gmrId = %u, offset = %u\n", __FUNCTION__,
               region->ptr.gmrId, region->ptr.offset);
-   --region->map_count;
+
+   os_munmap(region->data, region->size);
+   region->data = NULL;
 }
 
 /**