Re: [PATCH] dma-direct: fix DMA_ATTR_NO_KERNEL_MAPPING

[Walter Wu]

Hi Cristoph,

On Tue, 2021-11-02 at 07:41 +0100, Christoph Hellwig wrote:
> As others pointed out, DMA_ATTR_NO_KERNEL_MAPPING just means the
> caller can't rely on a kernel mapping.  So the "fix" here is
> wrong.  That being said for cases where we can easily remove a page
> from the kernel mapping it would be nice to do to:
> 
>  a) improve security
>  b) as a debug check to see that no one actually tries to access it
> 

I will modify my commit message. Thanks for your comment.

> > +		/* remove kernel mapping for pages */
> > +		set_memory_valid((unsigned
> > long)phys_to_virt(dma_to_phys(dev, *dma_handle)),
> 
> Please avoid overly long lines.  Also this function only exists for
> arm64
> also and others pointed out won't work for all cases.

Got it. I will send v2 patch.

Thanks for your review and suggestion.


Walter