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

[Christophe Leroy]

Le 03/04/2020 à 15:26, Nicholas Piggin a écrit :
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 <mah...@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npig...@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

#ifdef not needed, see below

+       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

This ifdef is not needed. FW_FEATURE_LPAR is only possible on 
CONFIG_PPC_BOOK3S_64 (indeed only on PSERIES or PS3). On others 
firmware_has_feature(FW_FEATURE_LPAR) should return 0 at compile time.

+       mce_limit = limit;
+       if (firmware_has_feature(FW_FEATURE_LPAR) && mce_limit > 
4UL*1024*1024*1024)
+               mce_limit = 4UL*1024*1024*1024;

You should use SZ_4G instead of hardcoding.

+#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
        }
  }


Christophe