From patchwork series 394930

https://patchwork.ozlabs.org//project/linuxppc-dev/list/?series=394930

Author: Fox Snowpatch

arch/powerpc/include/asm/interrupt.h

@@ -336,6 +336,14 @@ static inline void interrupt_nmi_enter_prepare(struct pt_regs *regs, struct inte
 	if (IS_ENABLED(CONFIG_KASAN))
 		return;
 
+	/*
+	 * Likewise, do not use it in real mode if percpu first chunk is not
+	 * embedded. With CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK enabled there
+	 * are chances where percpu allocation can come from vmalloc area.
+	 */
+	if (IS_ENABLED(CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK) && !is_embed_first_chunk)
+		return;
+
 	/* Otherwise, it should be safe to call it */
 	nmi_enter();
 }
@@ -351,6 +359,8 @@ static inline void interrupt_nmi_exit_prepare(struct pt_regs *regs, struct inter
 		// no nmi_exit for a pseries hash guest taking a real mode exception
 	} else if (IS_ENABLED(CONFIG_KASAN)) {
 		// no nmi_exit for KASAN in real mode
+	} else if (IS_ENABLED(CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK) && !is_embed_first_chunk) {
+		// no nmi_exit if percpu first chunk is not embedded
 	} else {
 		nmi_exit();
 	}

arch/powerpc/include/asm/percpu.h

@@ -15,6 +15,16 @@
 #endif /* CONFIG_SMP */
 #endif /* __powerpc64__ */
 
+#ifdef CONFIG_PPC64
+#include <linux/jump_label.h>
+DECLARE_STATIC_KEY_FALSE(__percpu_embed_first_chunk);
+
+#define is_embed_first_chunk	\
+		(static_key_enabled(&__percpu_embed_first_chunk.key))
+#else
+#define is_embed_first_chunk	(true)
+#endif /* CONFIG_PPC64 */
+
 #include <asm-generic/percpu.h>
 
 #include <asm/paca.h>

arch/powerpc/kernel/setup_64.c

@@ -834,6 +834,7 @@ static __init int pcpu_cpu_to_node(int cpu)
 
 unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
 EXPORT_SYMBOL(__per_cpu_offset);
+DEFINE_STATIC_KEY_FALSE(__percpu_embed_first_chunk);
 
 void __init setup_per_cpu_areas(void)
 {
@@ -869,6 +870,9 @@ void __init setup_per_cpu_areas(void)
 			pr_warn("PERCPU: %s allocator failed (%d), "
 				"falling back to page size\n",
 				pcpu_fc_names[pcpu_chosen_fc], rc);
+		else {
+			static_key_enable(&__percpu_embed_first_chunk.key);
+		}
 	}
 
 	if (rc < 0)