uml: runtime host VMSPLIT detection

Calculate TASK_SIZE at run-time by figuring out the host's VMSPLIT - this is
needed on i386 if UML is to run on hosts with varying VMSPLITs without
recompilation.

TASK_SIZE is now defined in terms of a variable, task_size.  This gets rid of
an include of pgtable.h from processor.h, which can cause include loops.

On i386, task_size is calculated early in boot by probing the address space in
a binary search to figure out where the boundary between usable and non-usable
memory is.  This tries to make sure that a page that is considered to be in
userspace is, or can be made, read-write.  I'm concerned about a system-global
VDSO page in kernel memory being hit and considered to be a userspace page.

On x86_64, task_size is just the old value of CONFIG_TOP_ADDR.

A bunch of config variable are gone now.  CONFIG_TOP_ADDR is directly replaced
by TASK_SIZE.  NEST_LEVEL is gone since the relocation of the stubs makes it
irrelevant.  All the HOST_VMSPLIT stuff is gone.  All references to these in
arch/um/Makefile are also gone.

I noticed and fixed a missing extern in os.h when adding os_get_task_size.

Note: This has been revised to fix the 32-bit UML on 64-bit host bug that
Miklos ran into.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 6 insertions, 1 deletions

diff --git a/arch/um/include/as-layout.h b/arch/um/include/as-layout.h
index 606bb5c..cac542d 100644
--- a/arch/um/include/as-layout.h
+++ b/arch/um/include/as-layout.h
@@ -57,6 +57,8 @@ extern unsigned long _stext, _etext, _sdata, _edata, __bss_start, _end;
 extern unsigned long _unprotected_end;
 extern unsigned long brk_start;
 
+extern unsigned long host_task_size;
+
 extern int linux_main(int argc, char **argv);
 
 extern void (*sig_info[])(int, struct uml_pt_regs *);
diff --git a/arch/um/include/os.h b/arch/um/include/os.h
index 0b6b627..32c799e 100644
--- a/arch/um/include/os.h
+++ b/arch/um/include/os.h
@@ -295,6 +295,9 @@ extern void maybe_sigio_broken(int fd, int read);
 extern int os_arch_prctl(int pid, int code, unsigned long *addr);
 
 /* tty.c */
-int get_pty(void);
+extern int get_pty(void);
+
+/* sys-$ARCH/task_size.c */
+extern unsigned long os_get_task_size(void);
 
 #endif