[PATCH v2 08/12] powerpc/pseries: limit machine check stack to 4GB

[Nicholas Piggin]

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

Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
 arch/powerpc/kernel/setup_64.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 3bf03666ee09..ca1041f8a578 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -695,6 +695,9 @@ 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;
 
        /*
@@ -713,6 +716,16 @@ 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.
+        */
+       mce_limit = limit;
+       if (firmware_has_feature(FW_FEATURE_LPAR) && mce_limit > 
4UL*1024*1024*1024)
+               mce_limit = 4UL*1024*1024*1024;
+
        for_each_possible_cpu(i) {
                paca_ptrs[i]->emergency_sp = alloc_stack(limit, i) + 
THREAD_SIZE;
 
@@ -721,7 +734,7 @@ 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