From d2cbbd45d433b96e41711a293e59cff259143694 Mon Sep 17 00:00:00 2001
From: Nicholas Piggin <npiggin@gmail.com>
Date: Fri, 8 May 2020 14:34:01 +1000
Subject: [PATCH] powerpc/pseries: Limit machine check stack to 4GB
References: bsc#1094244 ltc#168122
Patch-mainline: v5.8-rc1
Git-commit: d2cbbd45d433b96e41711a293e59cff259143694
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 <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Link: https://lore.kernel.org/r/20200508043408.886394-10-npiggin@gmail.com
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
arch/powerpc/kernel/setup_64.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -666,7 +666,7 @@ static void emerg_stack_init_thread_info
*/
void __init emergency_stack_init(void)
{
- u64 limit;
+ u64 limit, mce_limit;
unsigned int i;
/*
@@ -683,7 +683,16 @@ 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) {
struct thread_info *ti;
@@ -700,7 +709,7 @@ void __init emergency_stack_init(void)
paca[i].nmi_emergency_sp = (void *)ti + THREAD_SIZE;
/* emergency stack for machine check exception handling. */
- ti = __va(memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit));
+ ti = __va(memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, mce_limit));
memset(ti, 0, THREAD_SIZE);
emerg_stack_init_thread_info(ti, i);
paca[i].mc_emergency_sp = (void *)ti + THREAD_SIZE;