[PATCH 5/5] stack overflow safe kdump (2.6.15-i386) - private nmi stack

[Fernando Luis Vazquez Cao <fernando@intellilink.co.jp>]

Use a private NMI stack.

---
diff -urNp linux-2.6.15/arch/i386/kernel/irq.c
linux-2.6.15-sov/arch/i386/kernel/irq.c
--- linux-2.6.15/arch/i386/kernel/irq.c	2006-01-03 12:21:10.000000000
+0900
+++ linux-2.6.15-sov/arch/i386/kernel/irq.c	2006-01-16
22:04:07.000000000 +0900
@@ -37,11 +37,6 @@ void ack_bad_irq(unsigned int irq)
 /*
  * per-CPU IRQ handling contexts (thread information and stack)
  */
-union irq_ctx {
-	struct thread_info      tinfo;
-	u32                     stack[THREAD_SIZE/sizeof(u32)];
-};
-
 static union irq_ctx *hardirq_ctx[NR_CPUS];
 static union irq_ctx *softirq_ctx[NR_CPUS];
 #endif
@@ -154,6 +149,8 @@ void irq_ctx_init(int cpu)
 
 	printk("CPU %u irqstacks, hard=%p soft=%p\n",
 		cpu,hardirq_ctx[cpu],softirq_ctx[cpu]);
+
+	nmi_ctx_init(cpu);
 }
 
 void irq_ctx_exit(int cpu)
diff -urNp linux-2.6.15/arch/i386/kernel/traps.c
linux-2.6.15-sov/arch/i386/kernel/traps.c
--- linux-2.6.15/arch/i386/kernel/traps.c	2006-01-16 22:00:54.000000000
+0900
+++ linux-2.6.15-sov/arch/i386/kernel/traps.c	2006-01-16
22:05:51.000000000 +0900
@@ -643,6 +643,13 @@ static int dummy_nmi_callback(struct pt_
  
 static nmi_callback_t nmi_callback = dummy_nmi_callback;
 
+#ifdef CONFIG_4KSTACKS
+/*
+ * per-CPU NMI handling contexts (thread information and stack)
+ */
+static union irq_ctx *nmi_ctx[NR_CPUS];
+#endif /* CONFIG_4KSTACKS */
+
 static fastcall unsigned int __do_nmi(struct pt_regs * regs, long
error_code)
 {
 	int cpu;
@@ -657,7 +664,43 @@ static fastcall unsigned int __do_nmi(st
 	return 0;
 }
 
+#ifdef CONFIG_4KSTACKS
+#define _do_nmi(regs, error_code, nmih)					\
+{									\
+	union irq_ctx *curctx, *nmictx;					\
+	u32 *isp;							\
+									\
+	curctx = (union irq_ctx *) current_thread_info();		\
+	nmictx = nmi_ctx[safe_smp_processor_id()];			\
+									\
+	/*								\
+	 * This is where we switch to the NMI stack.			\
+	 */								\
+	if (curctx != nmictx) {						\
+		int arg1, arg2, ebx;					\
+									\
+		/* build the stack frame on the IRQ stack */		\
+		isp = (u32*) ((char *)nmictx + sizeof(*nmictx)); 	\
+		if (!virt_addr_valid(curctx))				\
+			nmictx->tinfo.task = NULL;			\
+		else							\
+			nmictx->tinfo.task = curctx->tinfo.task;	\
+		nmictx->tinfo.previous_esp = current_stack_pointer;	\
+									\
+		asm volatile (						\
+			"	xchgl	%%ebx,%%esp	\n"		\
+			"	call	"#nmih"		\n"		\
+			"	movl	%%ebx,%%esp	\n"		\
+			: "=a" (arg1), "=d" (arg2), "=b" (ebx)		\
+			:  "0" (regs),  "1" (error_code), "2" (isp)	\
+			: "memory", "cc", "ecx"				\
+		);							\
+	} else								\
+		nmih(regs, error_code);					\
+}
+#else /* CONFIG_4KSTACKS */
 #define _do_nmi(regs, error_code, nmih) nmih(regs, error_code);
+#endif /* CONFIG_4KSTACKS */
 
 fastcall void do_nmi(struct pt_regs * regs, long error_code)
 {
@@ -696,6 +739,46 @@ void set_crash_nmi_callback(nmi_callback
 }
 EXPORT_SYMBOL_GPL(set_crash_nmi_callback);
 
+#ifdef CONFIG_4KSTACKS
+
+/*
+ * These should really be __section__(".bss.page_aligned") as well, but
+ * gcc's 3.0 and earlier don't handle that correctly.
+ * NOTE: support for gcc 3.0 and earlier will eventually be dropped
+ */
+
+static char nmi_stack[NR_CPUS * THREAD_SIZE]
+		__attribute__((__aligned__(THREAD_SIZE)));
+
+/*
+ * Allocate per-cpu stacks for NMI processing
+ */
+void nmi_ctx_init(int cpu)
+{
+	union irq_ctx *irqctx;
+
+	if (nmi_ctx[cpu])
+		return;
+
+	irqctx = (union irq_ctx*) &nmi_stack[cpu*THREAD_SIZE];
+	irqctx->tinfo.task		= NULL;
+	irqctx->tinfo.exec_domain	= NULL;
+	irqctx->tinfo.cpu		= cpu;
+	irqctx->tinfo.preempt_count	= HARDIRQ_OFFSET;
+	irqctx->tinfo.addr_limit	= MAKE_MM_SEG(0);
+
+	nmi_ctx[cpu] = irqctx;
+
+	printk("CPU %u nmistack=%p\n", cpu, nmi_ctx[cpu]);
+}
+
+void nmi_ctx_exit(int cpu)
+{
+	nmi_ctx[cpu] = NULL;
+}
+
+#endif /* CONFIG_4KSTACKS */
+
 #ifdef CONFIG_KPROBES
 fastcall void __kprobes do_int3(struct pt_regs *regs, long error_code)
 {
diff -urNp linux-2.6.15/include/asm-i386/irq.h
linux-2.6.15-sov/include/asm-i386/irq.h
--- linux-2.6.15/include/asm-i386/irq.h	2006-01-03 12:21:10.000000000
+0900
+++ linux-2.6.15-sov/include/asm-i386/irq.h	2006-01-16
22:04:07.000000000 +0900
@@ -28,12 +28,21 @@ extern void release_vm86_irqs(struct tas
 #endif
 
 #ifdef CONFIG_4KSTACKS
-  extern void irq_ctx_init(int cpu);
-  extern void irq_ctx_exit(int cpu);
+union irq_ctx {
+	struct thread_info	tinfo;
+	u32			stack[THREAD_SIZE/sizeof(u32)];
+};
+
+extern void irq_ctx_init(int cpu);
+extern void irq_ctx_exit(int cpu);
+extern void nmi_ctx_init(int cpu);
+extern void nmi_ctx_exit(int cpu);
 # define __ARCH_HAS_DO_SOFTIRQ
 #else
 # define irq_ctx_init(cpu) do { } while (0)
 # define irq_ctx_exit(cpu) do { } while (0)
+# define nmi_ctx_init(cpu) do { } while (0)
+# define nmi_ctx_exit(cpu) do { } while (0)
 #endif
 
 #ifdef CONFIG_IRQBALANCE