Re: [RFC PATCH 01/14] fs/proc/vmcore: Update read_from_oldmem() for user pointer

On Mon, Dec 06, 2021 at 03:07:15PM +0000, Matthew Wilcox wrote:

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What do you think to adding a generic copy_pfn_to_iter()?  Not sure
which APIs to use to implement it ... some architectures have weird
requirements about which APIs can be used for what kinds of PFNs.

Hmm.  I though kmap_local_pfn(_prot) is all we need?

In the !HIGHMEM case, that calls pfn_to_page(), and I think the
point of this path is that we don't have a struct page for this pfn.

Indeed.  But to me this suggest that the !highmem stub is broken and
we should probably fix it rather than adding yet another interface.