mm/memory_hotplug: drop the flags field from struct mhp_restrictions

Patch series "Allow setting caching mode in arch_add_memory() for
P2PDMA", v4.

Currently, the page tables created using memremap_pages() are always
created with the PAGE_KERNEL cacheing mode.  However, the P2PDMA code is
creating pages for PCI BAR memory which should never be accessed through
the cache and instead use either WC or UC.  This still works in most
cases, on x86, because the MTRR registers typically override the caching
settings in the page tables for all of the IO memory to be UC-.
However, this tends not to work so well on other arches or some rare x86
machines that have firmware which does not setup the MTRR registers in
this way.

Instead of this, this series proposes a change to arch_add_memory() to
take the pgprot required by the mapping which allows us to explicitly
set pagetable entries for P2PDMA memory to UC.

This changes is pretty routine for most of the arches: x86_64, arm64 and
powerpc simply need to thread the pgprot through to where the page
tables are setup.  x86_32 unfortunately sets up the page tables at boot
so must use _set_memory_prot() to change their caching mode.  ia64, s390
and sh don't appear to have an easy way to change the page tables so,
for now at least, we just return -EINVAL on such mappings and thus they
will not support P2PDMA memory until the work for this is done.  This
should be fine as they don't yet support ZONE_DEVICE.

This patch (of 7):

This variable is not used anywhere and should therefore be removed from
the structure.

Signed-off-by: Logan Gunthorpe <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Reviewed-by: Dan Williams <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Eric Badger <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Paul Mackerras <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/memory_hotplug.h

@@ -59,11 +59,9 @@ enum {
 
 /*
  * Restrictions for the memory hotplug:
- * flags:  MHP_ flags
  * altmap: alternative allocator for memmap array
  */
 struct mhp_restrictions {
-	unsigned long flags;
 	struct vmem_altmap *altmap;
 };