[PATCH v3 10/15] powerpc/pseries: machine check use rtas_call_unlocked with args on stack

[Nicholas Piggin <npiggin@gmail.com>]

With the previous patch, machine checks can use rtas_call_unlocked
which avoids the rtas spinlock which would deadlock if a machine
check hits while making an rtas call.

This also avoids the complex rtas error logging which has more rtas calls
and includes kmalloc (which can return memory beyond RMA, which would
also crash).

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/platforms/pseries/ras.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/ras.c b/arch/powerpc/platforms/pseries/ras.c
index d65bc38bcb8f..4fd138ae26fd 100644
--- a/arch/powerpc/platforms/pseries/ras.c
+++ b/arch/powerpc/platforms/pseries/ras.c
@@ -468,7 +468,15 @@ static struct rtas_error_log *fwnmi_get_errinfo(struct pt_regs *regs)
  */
 static void fwnmi_release_errinfo(void)
 {
-	int ret = rtas_call(ibm_nmi_interlock_token, 0, 1, NULL);
+	struct rtas_args rtas_args;
+	int ret;
+
+	/*
+	 * On pseries, the machine check stack is limited to under 4GB, so
+	 * args can be on-stack.
+	 */
+	rtas_call_unlocked(&rtas_args, ibm_nmi_interlock_token, 0, 1, NULL);
+	ret = be32_to_cpu(rtas_args.rets[0]);
 	if (ret != 0)
 		printk(KERN_ERR "FWNMI: nmi-interlock failed: %d\n", ret);
 }
-- 
2.23.0