Metag architecture and related fixes for v3.15

Mostly fixes for metag and parisc relating to upgrowing stacks.
 
 * Fix missing compiler barriers in metag memory barriers.
 * Fix BUG_ON on metag when RLIMIT_STACK hard limit is increased beyond
   safe value.
 * Make maximum stack size configurable. This reduces the default user
   stack size back to 80MB (especially on parisc after their removal of
   _STK_LIM_MAX override). This only affects metag and parisc.
 * Remove metag _STK_LIM_MAX override to match other arches and follow
   parisc, now that it is safe to do so (due to the BUG_ON fix mentioned
   above).
 * Finally now that both metag and parisc _STK_LIM_MAX overrides have
   been removed, it makes sense to remove _STK_LIM_MAX altogether.
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Merge tag 'metag-for-v3.15-2' of git://git.kernel.org/pub/scm/linux/kernel/git/jhogan/metag

Pull Metag architecture and related fixes from James Hogan:
 "Mostly fixes for metag and parisc relating to upgrowing stacks.

   - Fix missing compiler barriers in metag memory barriers.
   - Fix BUG_ON on metag when RLIMIT_STACK hard limit is increased
     beyond safe value.
   - Make maximum stack size configurable.  This reduces the default
     user stack size back to 80MB (especially on parisc after their
     removal of _STK_LIM_MAX override).  This only affects metag and
     parisc.
   - Remove metag _STK_LIM_MAX override to match other arches and follow
     parisc, now that it is safe to do so (due to the BUG_ON fix
     mentioned above).
   - Finally now that both metag and parisc _STK_LIM_MAX overrides have
     been removed, it makes sense to remove _STK_LIM_MAX altogether"

* tag 'metag-for-v3.15-2' of git://git.kernel.org/pub/scm/linux/kernel/git/jhogan/metag:
  asm-generic: remove _STK_LIM_MAX
  metag: Remove _STK_LIM_MAX override
  parisc,metag: Do not hardcode maximum userspace stack size
  metag: Reduce maximum stack size to 256MB
  metag: fix memory barriers

arch/metag/include/asm/barrier.h

@@ -15,6 +15,7 @@ static inline void wr_fence(void)
 	volatile int *flushptr = (volatile int *) LINSYSEVENT_WR_FENCE;
 	barrier();
 	*flushptr = 0;
+	barrier();
 }
 
 #else /* CONFIG_METAG_META21 */
@@ -35,6 +36,7 @@ static inline void wr_fence(void)
 	*flushptr = 0;
 	*flushptr = 0;
 	*flushptr = 0;
+	barrier();
 }
 
 #endif /* !CONFIG_METAG_META21 */
@@ -68,6 +70,7 @@ static inline void fence(void)
 	volatile int *flushptr = (volatile int *) LINSYSEVENT_WR_ATOMIC_UNLOCK;
 	barrier();
 	*flushptr = 0;
+	barrier();
 }
 #define smp_mb()        fence()
 #define smp_rmb()       fence()

arch/metag/include/asm/processor.h

@@ -22,6 +22,8 @@
 /* Add an extra page of padding at the top of the stack for the guard page. */
 #define STACK_TOP	(TASK_SIZE - PAGE_SIZE)
 #define STACK_TOP_MAX	STACK_TOP
+/* Maximum virtual space for stack */
+#define STACK_SIZE_MAX	(CONFIG_MAX_STACK_SIZE_MB*1024*1024)
 
 /* This decides where the kernel will search for a free chunk of vm
  * space during mmap's.

arch/metag/include/uapi/asm/Kbuild

@@ -4,11 +4,11 @@ include include/uapi/asm-generic/Kbuild.asm
 header-y += byteorder.h
 header-y += ech.h
 header-y += ptrace.h
-header-y += resource.h
 header-y += sigcontext.h
 header-y += siginfo.h
 header-y += swab.h
 header-y += unistd.h
 
 generic-y += mman.h
+generic-y += resource.h
 generic-y += setup.h

arch/metag/include/uapi/asm/resource.h

@@ -1,7 +0,0 @@
-#ifndef _UAPI_METAG_RESOURCE_H
-#define _UAPI_METAG_RESOURCE_H
-
-#define _STK_LIM_MAX    (1 << 28)
-#include <asm-generic/resource.h>
-
-#endif /* _UAPI_METAG_RESOURCE_H */

arch/parisc/include/asm/processor.h

@@ -55,6 +55,11 @@
 #define STACK_TOP	TASK_SIZE
 #define STACK_TOP_MAX	DEFAULT_TASK_SIZE
 
+/* Allow bigger stacks for 64-bit processes */
+#define STACK_SIZE_MAX	(USER_WIDE_MODE					\
+			 ? (1 << 30)	/* 1 GB */			\
+			 : (CONFIG_MAX_STACK_SIZE_MB*1024*1024))
+
 #endif
 
 #ifndef __ASSEMBLY__

arch/parisc/kernel/sys_parisc.c

@@ -72,10 +72,10 @@ static unsigned long mmap_upper_limit(void)
 {
 	unsigned long stack_base;
 
-	/* Limit stack size to 1GB - see setup_arg_pages() in fs/exec.c */
+	/* Limit stack size - see setup_arg_pages() in fs/exec.c */
 	stack_base = rlimit_max(RLIMIT_STACK);
-	if (stack_base > (1 << 30))
-		stack_base = 1 << 30;
+	if (stack_base > STACK_SIZE_MAX)
+		stack_base = STACK_SIZE_MAX;
 
 	return PAGE_ALIGN(STACK_TOP - stack_base);
 }

fs/exec.c

@@ -657,10 +657,10 @@ int setup_arg_pages(struct linux_binprm *bprm,
 	unsigned long rlim_stack;
 
 #ifdef CONFIG_STACK_GROWSUP
-	/* Limit stack size to 1GB */
+	/* Limit stack size */
 	stack_base = rlimit_max(RLIMIT_STACK);
-	if (stack_base > (1 << 30))
-		stack_base = 1 << 30;
+	if (stack_base > STACK_SIZE_MAX)
+		stack_base = STACK_SIZE_MAX;
 
 	/* Make sure we didn't let the argument array grow too large. */
 	if (vma->vm_end - vma->vm_start > stack_base)

include/asm-generic/resource.h

@@ -12,7 +12,7 @@
 	[RLIMIT_CPU]		= {  RLIM_INFINITY,  RLIM_INFINITY },	\
 	[RLIMIT_FSIZE]		= {  RLIM_INFINITY,  RLIM_INFINITY },	\
 	[RLIMIT_DATA]		= {  RLIM_INFINITY,  RLIM_INFINITY },	\
-	[RLIMIT_STACK]		= {       _STK_LIM,   _STK_LIM_MAX },	\
+	[RLIMIT_STACK]		= {       _STK_LIM,  RLIM_INFINITY },	\
 	[RLIMIT_CORE]		= {              0,  RLIM_INFINITY },	\
 	[RLIMIT_RSS]		= {  RLIM_INFINITY,  RLIM_INFINITY },	\
 	[RLIMIT_NPROC]		= {              0,              0 },	\

include/uapi/asm-generic/resource.h

@@ -57,12 +57,5 @@
 # define RLIM_INFINITY		(~0UL)
 #endif
 
-/*
- * RLIMIT_STACK default maximum - some architectures override it:
- */
-#ifndef _STK_LIM_MAX
-# define _STK_LIM_MAX		RLIM_INFINITY
-#endif
-
 
 #endif /* _UAPI_ASM_GENERIC_RESOURCE_H */

mm/Kconfig

@@ -581,3 +581,18 @@ config PGTABLE_MAPPING
 
 config GENERIC_EARLY_IOREMAP
 	bool
+
+config MAX_STACK_SIZE_MB
+	int "Maximum user stack size for 32-bit processes (MB)"
+	default 80
+	range 8 256 if METAG
+	range 8 2048
+	depends on STACK_GROWSUP && (!64BIT || COMPAT)
+	help
+	  This is the maximum stack size in Megabytes in the VM layout of 32-bit
+	  user processes when the stack grows upwards (currently only on parisc
+	  and metag arch). The stack will be located at the highest memory
+	  address minus the given value, unless the RLIMIT_STACK hard limit is
+	  changed to a smaller value in which case that is used.
+
+	  A sane initial value is 80 MB.