Re: [PATCH V2 4/4] misc: vop: mapping kernel memory to user space as noncached

Christoph Hellwig
2020-09-29T10:28:44Z

On Tue, Sep 29, 2020 at 04:44:25PM +0800, Sherry Sun wrote:
> Mapping kernel space memory to user space as noncached, since user space
> need check the updates of avail_idx and device page flags timely.
>
> Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
> Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
> ---
> drivers/misc/mic/vop/vop_vringh.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/misc/mic/vop/vop_vringh.c b/drivers/misc/mic/vop/vop_vringh.c
> index 4d5feb39aeb7..6e193bd64ef1 100644
> --- a/drivers/misc/mic/vop/vop_vringh.c
> +++ b/drivers/misc/mic/vop/vop_vringh.c
> @@ -1057,7 +1057,7 @@ static int vop_mmap(struct file *f, struct vm_area_struct *vma)
> }
> err = remap_pfn_range(vma, vma->vm_start + offset,
> pa >> PAGE_SHIFT, size,
> - vma->vm_page_prot);
> + pgprot_noncached(vma->vm_page_prot));

You can't call remap_pfn_range on memory returned from
dma_alloc_coherent (which btw is not marked uncached on many platforms).

You need to use the dma_mmap_coherent helper instead. And this also
needs to go into the first patch.