coredump: add DAX filtering for FDPIC ELF coredumps

Add explicit filtering for DAX mappings to FDPIC ELF coredump.  This is
useful because DAX mappings have the potential to be very large.

This patch has only been compile tested.
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

fs/binfmt_elf_fdpic.c

@@ -35,6 +35,7 @@
 #include <linux/elf-fdpic.h>
 #include <linux/elfcore.h>
 #include <linux/coredump.h>
+#include <linux/dax.h>
 
 #include <asm/uaccess.h>
 #include <asm/param.h>
@@ -1206,6 +1207,20 @@ static int maydump(struct vm_area_struct *vma, unsigned long mm_flags)
 		return 0;
 	}
 
+	/* support for DAX */
+	if (vma_is_dax(vma)) {
+		if (vma->vm_flags & VM_SHARED) {
+			dump_ok = test_bit(MMF_DUMP_DAX_SHARED, &mm_flags);
+			kdcore("%08lx: %08lx: %s (DAX shared)", vma->vm_start,
+			       vma->vm_flags, dump_ok ? "yes" : "no");
+		} else {
+			dump_ok = test_bit(MMF_DUMP_DAX_PRIVATE, &mm_flags);
+			kdcore("%08lx: %08lx: %s (DAX private)", vma->vm_start,
+			       vma->vm_flags, dump_ok ? "yes" : "no");
+		}
+		return dump_ok;
+	}
+
 	/* By default, dump shared memory if mapped from an anonymous file. */
 	if (vma->vm_flags & VM_SHARED) {
 		if (file_inode(vma->vm_file)->i_nlink == 0) {