Re: [PATCH V3 4/4] misc: vop: mapping kernel memory to user space as noncached

[Christoph Hellwig]

On Thu, Oct 22, 2020 at 01:06:38PM +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@xxxxxxx>
> Signed-off-by: Sherry Sun <sherry.sun@xxxxxxx>
> ---
>  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 b5612183dcb8..b75c2b713a3b 100644
> --- a/drivers/misc/mic/vop/vop_vringh.c
> +++ b/drivers/misc/mic/vop/vop_vringh.c
> @@ -1058,7 +1058,7 @@ 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));

Again, memory allocated using dma_alloc_coherent can only be mapped
using dma_mmap_coherent, which will use the right attributes for the
mapping, which often are cached.