Re: [PATCH 5.15 1/2] dma-mapping: remove bogus test for pfn_valid from dma_map_resource

[Greg KH <greg@kroah.com>]

On Wed, Apr 20, 2022 at 05:43:40AM -0700, Georgi Djakov wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> [ Upstream commit a9c38c5d267cb94871dfa2de5539c92025c855d7 ]
> 
> dma_map_resource() uses pfn_valid() to ensure the range is not RAM.
> However, pfn_valid() only checks for availability of the memory map for a
> PFN but it does not ensure that the PFN is actually backed by RAM.
> 
> As dma_map_resource() is the only method in DMA mapping APIs that has this
> check, simply drop the pfn_valid() test from dma_map_resource().
> 
> Link: https://lore.kernel.org/all/20210824173741.GC623@arm.com/
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Acked-by: David Hildenbrand <david@redhat.com>
> Link: https://lore.kernel.org/r/20210930013039.11260-2-rppt@kernel.org
> Signed-off-by: Will Deacon <will@kernel.org>
> Fixes: 859a85ddf90e ("mm: remove pfn_valid_within() and CONFIG_HOLES_IN_ZONE")
> Link: https://lore.kernel.org/r/Yl0IZWT2nsiYtqBT@linux.ibm.com
> Signed-off-by: Georgi Djakov <quic_c_gdjako@quicinc.com>
> ---
>  kernel/dma/mapping.c | 4 ----
>  1 file changed, 4 deletions(-)

I took this, but I do not understand why patch 2/2 in this series is
needed, as Sasha points out.  Cleanups are nice, but is it necessary
here?

thanks,

greg k-h