[PATCH 4.15 021/163] powerpc/vas: Dont set uses_vas for kernel windows

[Greg Kroah-Hartman]

4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nicholas Piggin <npiggin@xxxxxxxxx>

commit b00b62898631b756c3e123542bbb0487aa343dd9 upstream.

cp_abort is only required for user windows, because kernel context
must not be preempted between a copy/paste pair.

Without this patch, the init task gets used_vas set when it runs the
nx842_powernv_init initcall, which opens windows for kernel usage.

used_vas is then never cleared anywhere, so it gets propagated into
all other tasks. It's a property of the address space, so it should
really be cleared when a new mm is created (or in dup_mmap if the
mmaps are marked as VM_DONTCOPY). For now we seem to have no such
driver, so leave that for another patch.

Fixes: 6c8e6bb2a52d ("powerpc/vas: Add support for user receive window")
Cc: stable@xxxxxxxxxxxxxxx # v4.15+
Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Reviewed-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/powerpc/platforms/powernv/vas-window.c |   16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

--- a/arch/powerpc/platforms/powernv/vas-window.c
+++ b/arch/powerpc/platforms/powernv/vas-window.c
@@ -1063,16 +1063,16 @@ struct vas_window *vas_tx_win_open(int v
 			rc = PTR_ERR(txwin->paste_kaddr);
 			goto free_window;
 		}
+	} else {
+		/*
+		 * A user mapping must ensure that context switch issues
+		 * CP_ABORT for this thread.
+		 */
+		rc = set_thread_uses_vas();
+		if (rc)
+			goto free_window;
 	}
 
-	/*
-	 * Now that we have a send window, ensure context switch issues
-	 * CP_ABORT for this thread.
-	 */
-	rc = -EINVAL;
-	if (set_thread_uses_vas() < 0)
-		goto free_window;
-
 	set_vinst_win(vinst, txwin);
 
 	return txwin;