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>

1 files changed, 0 insertions, 11 deletions

diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index 99e51d059a02..dba8e05f0287 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -203,17 +203,6 @@ config NR_CPUS
         depends on SMP
         default "32"
 
-config NEST_LEVEL
-        int "Nesting level"
-        default "0"
-        help
-          This is set to the number of layers of UMLs that this UML will be run
-          in.  Normally, this is zero, meaning that it will run directly on the
-          host.  Setting it to one will build a UML that can run inside a UML
-          that is running on the host.  Generally, if you intend this UML to run
-          inside another UML, set CONFIG_NEST_LEVEL to one more than the host
-          UML.
-
 config HIGHMEM
         bool "Highmem support (EXPERIMENTAL)"
         depends on !64BIT && EXPERIMENTAL