[PATCH] ia64: max user stack size of main thread configurable via RLIMIT_STACK

Make the size of the user stack based on the stack rlimit.
The stack hard stack size now defaults to 2GB, but can be increased
 with ulimit up to 1/2 of the max mappable space in a region.
For 16k pages, this makes the max stack size 8TB.

arch/ia64/mm/init.c

@@ -68,6 +68,16 @@ check_pgt_cache (void)
 	}
 }
 
+inline void
+ia64_set_rbs_bot (void)
+{
+	unsigned long stack_size = current->rlim[RLIMIT_STACK].rlim_max & -16;
+
+	if (stack_size > MAX_USER_STACK_SIZE)
+		stack_size = MAX_USER_STACK_SIZE;
+	current->thread.rbs_bot = STACK_TOP - stack_size;
+}
+
 /*
  * This performs some platform-dependent address space initialization.
  * On IA-64, we want to setup the VM area for the register backing
@@ -79,6 +89,8 @@ ia64_init_addr_space (void)
 {
 	struct vm_area_struct *vma;
 
+	ia64_set_rbs_bot();
+
 	/*
 	 * If we're out of memory and kmem_cache_alloc() returns NULL, we simply ignore
 	 * the problem.  When the process attempts to write to the register backing store
@@ -87,7 +99,7 @@ ia64_init_addr_space (void)
 	vma = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
 	if (vma) {
 		vma->vm_mm = current->mm;
-		vma->vm_start = IA64_RBS_BOT;
+		vma->vm_start = current->thread.rbs_bot;
 		vma->vm_end = vma->vm_start + PAGE_SIZE;
 		vma->vm_page_prot = protection_map[VM_DATA_DEFAULT_FLAGS & 0x7];
 		vma->vm_flags = VM_READ|VM_WRITE|VM_MAYREAD|VM_MAYWRITE|VM_GROWSUP;

include/asm-ia64/a.out.h

@@ -30,9 +30,6 @@ struct exec {
 #define N_TXTOFF(x)	0
 
 #ifdef __KERNEL__
-# include <asm/page.h>
-# define STACK_TOP	(0x6000000000000000UL + (1UL << (4*PAGE_SHIFT - 12)) - PAGE_SIZE)
-# define IA64_RBS_BOT	(STACK_TOP - 0x80000000L + PAGE_SIZE)	/* bottom of reg. backing store */
+#include <asm/ustack.h>
 #endif
-
 #endif /* _ASM_IA64_A_OUT_H */

include/asm-ia64/processor.h

@@ -17,6 +17,7 @@
 
 #include <asm/ptrace.h>
 #include <asm/kregs.h>
+#include <asm/ustack.h>
 
 #define IA64_NUM_DBG_REGS	8
 /*
@@ -235,6 +236,7 @@ struct thread_struct {
 	__u64 ksp;			/* kernel stack pointer */
 	__u64 map_base;			/* base address for get_unmapped_area() */
 	__u64 task_size;		/* limit for task size */
+	__u64 rbs_bot;			/* the base address for the RBS */
 	int last_fph_cpu;		/* CPU that may hold the contents of f32-f127 */
 
 #ifdef CONFIG_IA32_SUPPORT
@@ -283,6 +285,7 @@ struct thread_struct {
 	.on_ustack =	0,			\
 	.ksp =		0,			\
 	.map_base =	DEFAULT_MAP_BASE,	\
+	.rbs_bot =	DEFAULT_USER_STACK_SIZE,	\
 	.task_size =	DEFAULT_TASK_SIZE,	\
 	.last_fph_cpu =  -1,			\
 	INIT_THREAD_IA32			\
@@ -299,7 +302,7 @@ struct thread_struct {
 	regs->cr_iip = new_ip;									\
 	regs->ar_rsc = 0xf;		/* eager mode, privilege level 3 */			\
 	regs->ar_rnat = 0;									\
-	regs->ar_bspstore = IA64_RBS_BOT;							\
+	regs->ar_bspstore = current->thread.rbs_bot;						\
 	regs->ar_fpsr = FPSR_DEFAULT;								\
 	regs->loadrs = 0;									\
 	regs->r8 = current->mm->dumpable;	/* set "don't zap registers" flag */		\

include/asm-ia64/resource.h

@@ -8,6 +8,8 @@
  * Copyright (C) 1998, 1999 David Mosberger-Tang <davidm@hpl.hp.com>
  */
 
+#include <asm/ustack.h>
+
 #define RLIMIT_CPU	0		/* CPU time in ms */
 #define RLIMIT_FSIZE	1		/* Maximum filesize */
 #define RLIMIT_DATA	2		/* max data size */
@@ -35,7 +37,7 @@
 	{ RLIM_INFINITY, RLIM_INFINITY },		\
 	{ RLIM_INFINITY, RLIM_INFINITY },		\
 	{ RLIM_INFINITY, RLIM_INFINITY },		\
-	{      _STK_LIM, RLIM_INFINITY },		\
+	{      _STK_LIM, DEFAULT_USER_STACK_SIZE },	\
 	{             0, RLIM_INFINITY },		\
 	{ RLIM_INFINITY, RLIM_INFINITY },		\
 	{             0,             0 },		\

include/asm-ia64/ustack.h

+#ifndef _ASM_IA64_USTACK_H
+#define _ASM_IA64_USTACK_H
+
+/*
+ * Constants for the user stack size
+ */
+
+#include <asm/pgtable.h>
+
+/* The absolute hard limit for stack size is 1/2 of the mappable space in the region */
+#define MAX_USER_STACK_SIZE	(RGN_MAP_LIMIT/2)
+/* Make a default stack size of 2GB */
+#define DEFAULT_USER_STACK_SIZE	(1UL << 31)
+#define STACK_TOP		(0x6000000000000000UL + RGN_MAP_LIMIT)
+
+#endif /* _ASM_IA64_USTACK_H */