um: increase stack growth cushion in pagefault

analog of [PATCH] i386: let usermode execute the "enter" instruction from
circa 2006.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/x86/um/asm/processor.h

@@ -10,6 +10,9 @@
 # include "processor_64.h"
 #endif
 
+#define ARCH_IS_STACKGROW(address) \
+       (address + 65536 + 32 * sizeof(unsigned long) >= UPT_SP(&current->thread.regs.regs))
+
 #include <asm/processor-generic.h>
 
 #endif

arch/x86/um/asm/processor_32.h

@@ -63,9 +63,6 @@ static inline void rep_nop(void)
 #define current_text_addr() \
 	({ void *pc; __asm__("movl $1f,%0\n1:":"=g" (pc)); pc; })
 
-#define ARCH_IS_STACKGROW(address) \
-       (address + 32 >= UPT_SP(&current->thread.regs.regs))
-
 #define KSTK_EIP(tsk) KSTK_REG(tsk, EIP)
 #define KSTK_ESP(tsk) KSTK_REG(tsk, UESP)
 #define KSTK_EBP(tsk) KSTK_REG(tsk, EBP)

arch/x86/um/asm/processor_64.h

@@ -42,9 +42,6 @@ static inline void arch_copy_thread(struct arch_thread *from,
 #define current_text_addr() \
 	({ void *pc; __asm__("movq $1f,%0\n1:":"=g" (pc)); pc; })
 
-#define ARCH_IS_STACKGROW(address) \
-        (address + 128 >= UPT_SP(&current->thread.regs.regs))
-
 #define KSTK_EIP(tsk) KSTK_REG(tsk, RIP)
 #define KSTK_ESP(tsk) KSTK_REG(tsk, RSP)