[BUG 5.14] arm64/mm: dma memory mapping fails (in some cases)

[Mike Rapoport]

On Wed, Aug 25, 2021 at 12:38:31PM +0200, David Hildenbrand wrote:
> On 25.08.21 12:20, Catalin Marinas wrote:
>
> > I can see the documentation for pfn_valid() does not claim anything more
> > than the presence of an memmap entry. But I wonder whether the confusion
> > is wider-spread than just the DMA code. At a quick grep, try_ram_remap()
> > assumes __va() can be used on pfn_valid(), though I suspect it relies on
> > the calling function to check that the resource was RAM. The arm64
> > kern_addr_valid() returns true based on pfn_valid() and kcore.c uses
> > standard memcpy on it, which wouldn't work for I/O (should we change
> > this check to pfn_is_map_memory() for arm64?).
> 
> kern_addr_valid() checks that there is a direct map entry, and that the
> mapped address has a valid mmap. (copied from x86-64)
> 
> Would you expect to have a direct map for memory holes and similar (IOW,
> !System RAM)?

I don't see where will it bail out for an IOMEM mapping before doing the
pfn_valid() check...
 
-- 
Sincerely yours,
Mike.