On 11/04/2010 01:03 AM, Ben Skeggs wrote:
> From: Ben Skeggs<bskeggs at redhat.com>
>
> If the driver kmaps an object userspace is expecting to be mapped, the
> unmap would have called down into the drivers io_unreserve() function
> and potentially unmapped the pages from its BARs (for example) and they'd
> no longer be accessible for the userspace mapping.
>
> Signed-off-by: Ben Skeggs<bskeggs at redhat.com>
> ---
> drivers/gpu/drm/ttm/ttm_bo_util.c | 14 ++++++++++----
> include/drm/ttm/ttm_bo_api.h | 1 +
> 2 files changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c
> b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index ff358ad..e9dbe8b 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -467,9 +467,12 @@ int ttm_bo_kmap(struct ttm_buffer_object *bo,
> if (num_pages> 1&& !DRM_SUSER(DRM_CURPROC))
> return -EPERM;
> #endif
> - ret = ttm_mem_io_reserve(bo->bdev,&bo->mem);
> - if (ret)
> - return ret;
> + if (!bo->mem.bus.io_reserved) {
> + ret = ttm_mem_io_reserve(bo->bdev,&bo->mem);
> + if (ret)
> + return ret;
> + map->io_reserved = true;
> + }
> if (!bo->mem.bus.is_iomem) {
> return ttm_bo_kmap_ttm(bo, start_page, num_pages, map);
> } else {
> @@ -487,7 +490,10 @@ void ttm_bo_kunmap(struct ttm_bo_kmap_obj *map)
> switch (map->bo_kmap_type) {
> case ttm_bo_map_iomap:
> iounmap(map->virtual);
> - ttm_mem_io_free(map->bo->bdev,&map->bo->mem);
> + if (map->io_reserved) {
> + ttm_mem_io_free(map->bo->bdev,&map->bo->mem);
> + map->io_reserved = false;
> + }
> break;
> case ttm_bo_map_vmap:
> vunmap(map->virtual);
> diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
> index 5afa5b5..ce998ac 100644
> --- a/include/drm/ttm/ttm_bo_api.h
> +++ b/include/drm/ttm/ttm_bo_api.h
> @@ -300,6 +300,7 @@ struct ttm_bo_kmap_obj {
> ttm_bo_map_premapped = 4 | TTM_BO_MAP_IOMEM_MASK,
> } bo_kmap_type;
> struct ttm_buffer_object *bo;
> + bool io_reserved;
> };
>
> /**
>
This doesn't solve the problem unfortunately. Consider the sequence
kmap->io_mem_reserve
fault()->
kunmap->io_mem_free
user_space_access()-> Invalid.
I think this needs to be fixed by us maintaining an
mem:io_reserved_count, where all user-space triggered io_reserves count
as 1. A mem::user_space_io_reserved flag could be protected by the
bo::reserve lock, whereas a reserved_count can't, since strictly you're
allowed to kmap a bo without reserving it, but only if it's pinned
/Thomas
.
