[PATCH v2 09/14] powerpc/pseries: limit machine check stack to 4GB

[Nicholas Piggin <npiggin@gmail.com>]

This allows rtas_args to be put on the machine check stack, which
avoids a lot of complications with re-entrancy deadlocks.

Reviewed-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kernel/setup_64.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index e05e6dd67ae6..3a2428aa3d9a 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -692,6 +692,9 @@ void __init exc_lvl_early_init(void)
 void __init emergency_stack_init(void)
 {
 	u64 limit;
+#ifdef CONFIG_PPC_BOOK3S_64
+	u64 mce_limit;
+#endif
 	unsigned int i;
 
 	/*
@@ -710,6 +713,18 @@ void __init emergency_stack_init(void)
 	 */
 	limit = min(ppc64_bolted_size(), ppc64_rma_size);
 
+	/*
+	 * Machine check on pseries calls rtas, but can't use the static
+	 * rtas_args due to a machine check hitting while the lock is held.
+	 * rtas args have to be under 4GB, so the machine check stack is
+	 * limited to 4GB so args can be put on stack.
+	 */
+#ifdef CONFIG_PPC_BOOK3S_64
+	mce_limit = limit;
+	if (firmware_has_feature(FW_FEATURE_LPAR) && mce_limit > 4UL*1024*1024*1024)
+		mce_limit = 4UL*1024*1024*1024;
+#endif
+
 	for_each_possible_cpu(i) {
 		paca_ptrs[i]->emergency_sp = alloc_stack(limit, i) + THREAD_SIZE;
 
@@ -718,7 +733,7 @@ void __init emergency_stack_init(void)
 		paca_ptrs[i]->nmi_emergency_sp = alloc_stack(limit, i) + THREAD_SIZE;
 
 		/* emergency stack for machine check exception handling. */
-		paca_ptrs[i]->mc_emergency_sp = alloc_stack(limit, i) + THREAD_SIZE;
+		paca_ptrs[i]->mc_emergency_sp = alloc_stack(mce_limit, i) + THREAD_SIZE;
 #endif
 	}
 }
-- 
2.23.0