drivers/scsi/sg.c: mark VMA as VM_IO to prevent migration

Reduced testcase:

#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
#include <numaif.h>

#define SIZE 0x2000

int main()
{
int fd;
void *p;

fd = open("/dev/sg0", O_RDWR);
p = mmap(NULL, SIZE, PROT_EXEC, MAP_PRIVATE | MAP_LOCKED, fd, 0);
mbind(p, SIZE, 0, NULL, 0, MPOL_MF_MOVE);
return 0;
}

We shouldn't try to migrate pages in sg VMA as we don't have a way to
update Sg_scatter_hold::pages accordingly from mm core.

Let's mark the VMA as VM_IO to indicate to mm core that the VMA is not
migratable.

Signed-off-by: Kirill A. Shutemov <[e-mail]>
Reported-by: Dmitry Vyukov <[e-mail]>
Acked-by: Vlastimil Babka <[e-mail]>
Cc: Doug Gilbert <[e-mail]>
Cc: David Rientjes <[e-mail]>
Cc: Naoya Horiguchi <[e-mail]>
Cc: "Kirill A. Shutemov" <[e-mail]>
Cc: Shiraz Hashim <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Sasha Levin <[e-mail]>
Cc: syzkaller <[e-mail]>
Cc: Kostya Serebryany <[e-mail]>
Cc: Alexander Potapenko <[e-mail]>
Cc: James Bottomley <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/scsi/sg.c

···
 	}
 
 	sfp->mmap_called = 1;
-	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
+	vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
 	vma->vm_private_data = sfp;
 	vma->vm_ops = &sg_mmap_vm_ops;
 	return 0;