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

drivers/scsi/sg.c

@@ -1261,7 +1261,7 @@ sg_mmap(struct file *filp, struct vm_area_struct *vma)
 	}
 
 	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;