On Sun, Sep 10, 2023, at 14:52, Gregory Price wrote:

quoted

I'll clean up the current implementation for what I have on a v2 of an
RFC, and then look at adding some pull-ahead patches to fix both
move_pages and move_phys_pages for compat processes.  Might take me a
bit, I've only done compat work once before and I remember it being
annoying to get right.

I think what you want is roughly this (untested):

--- a/mm/migrate.c
+++ b/mm/migrate.c

@@ -2159,6 +2159,7 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
                         const int __user *nodes,
                         int __user *status, int flags)
 {
+       struct compat_uptr_t __user *compat_pages = (void __user *)pages;
        int current_node = NUMA_NO_NODE;
        LIST_HEAD(pagelist);
        int start, i;

@@ -2171,8 +2172,17 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
                int node;
 
                err = -EFAULT;
-               if (get_user(p, pages + i))
-                       goto out_flush;
+               if (in_compat_syscall() {
+                       compat_uptr_t cp;
+
+                       if (get_user(cp, compat_pages + i))
+                               goto out_flush;
+
+                       p = compat_ptr(cp);
+               } else {
+                       if (get_user(p, pages + i))
+                               goto out_flush;
+               }
                if (get_user(node, nodes + i))
                        goto out_flush;
 

alternatively you could use the get_compat_pages_array()
helper that is already used in the do_pages_stat()
function.