percpu: flush tlb in pcpu_reclaim_populated()

Prior to "percpu: implement partial chunk depopulation",
pcpu_depopulate_chunk() was called only on the destruction path. This
meant the virtual address range was on its way back to vmalloc which
will handle flushing the tlbs for us.

However, with pcpu_reclaim_populated(), we are now calling
pcpu_depopulate_chunk() during the active lifecycle of a chunk.
Therefore, we need to flush the tlb as well otherwise we can end up
accessing the wrong page through an invalid tlb mapping as reported in
[1].

[1] https://lore.kernel.org/lkml/20210702191140.GA3166599@roeck-us.net/

Fixes: f183324133ea ("percpu: implement partial chunk depopulation")
Reported-and-tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Dennis Zhou <dennis@kernel.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c
index ee5d89fcd66f..2054c9213c43 100644
--- a/mm/percpu-vm.c
+++ b/mm/percpu-vm.c
@@ -303,6 +303,9 @@ static int pcpu_populate_chunk(struct pcpu_chunk *chunk,
  * For each cpu, depopulate and unmap pages [@page_start,@page_end)
  * from @chunk.
  *
+ * Caller is required to call pcpu_post_unmap_tlb_flush() if not returning the
+ * region back to vmalloc() which will lazily flush the tlb.
+ *
  * CONTEXT:
  * pcpu_alloc_mutex.
  */
@@ -324,8 +327,6 @@ static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk,
 
 	pcpu_unmap_pages(chunk, pages, page_start, page_end);
 
-	/* no need to flush tlb, vmalloc will handle it lazily */
-
 	pcpu_free_pages(chunk, pages, page_start, page_end);
 }