[PATCH v4 09/16] 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.

Reviewed-by: Christophe Leroy <christophe.le...@c-s.fr>
Reviewed-by: Mahesh Salgaonkar <mah...@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
 arch/powerpc/kernel/setup_64.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 8105010b0e76..bb47555d48a2 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -711,7 +711,7 @@ void __init exc_lvl_early_init(void)
  */
 void __init emergency_stack_init(void)
 {
-       u64 limit;
+       u64 limit, mce_limit;
        unsigned int i;
 
        /*
@@ -728,7 +728,16 @@ void __init emergency_stack_init(void)
         * initialized in kernel/irq.c. These are initialized here in order
         * to have emergency stacks available as early as possible.
         */
-       limit = min(ppc64_bolted_size(), ppc64_rma_size);
+       limit = mce_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.
+        */
+       if (firmware_has_feature(FW_FEATURE_LPAR) && mce_limit > SZ_4G)
+               mce_limit = SZ_4G;
 
        for_each_possible_cpu(i) {
                paca_ptrs[i]->emergency_sp = alloc_stack(limit, i) + 
THREAD_SIZE;
@@ -738,7 +747,7 @@ 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