proc/kcore: do not try to access unaccepted memory

Support for unaccepted memory was added recently, refer commit
dcdfdd40fa82 ("mm: Add support for unaccepted memory"), whereby a virtual
machine may need to accept memory before it can be used.

Do not try to access unaccepted memory because it can cause the guest to
fail.

For /proc/kcore, which is read-only and does not support mmap, this means a
read of unaccepted memory will return zeros.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Adrian Hunter <[e-mail]>
Reviewed-by: David Hildenbrand <[e-mail]>
Cc: Ard Biesheuvel <[e-mail]>
Cc: Baoquan He <[e-mail]>
Cc: Borislav Petkov (AMD) <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: Dave Young <[e-mail]>
Cc: Kirill A. Shutemov <[e-mail]>
Cc: Lorenzo Stoakes <[e-mail]>
Cc: Mike Rapoport <[e-mail]>
Cc: Tom Lendacky <[e-mail]>
Cc: Vivek Goyal <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

fs/proc/kcore.c

···
 			 * and explicitly excluded physical ranges.
 			 */
 			if (!page || PageOffline(page) ||
-			    is_page_hwpoison(page) || !pfn_is_ram(pfn)) {
+			    is_page_hwpoison(page) || !pfn_is_ram(pfn) ||
+			    pfn_is_unaccepted_memory(pfn)) {
 				if (iov_iter_zero(tsz, iter) != tsz) {
 					ret = -EFAULT;
 					goto out;